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substrate utilization and respiration in relation to growth and maintenance inhighe r plants
F.W.T. PENNING DE VRIES
N08201.571 substrate utilization and respiration in relation to growth and maintenance inhighe r plants
F.W.T. PENNING DE VRIES SUBSTRATEUTILIZATIO NAN DRESPIRATIO N INRELATIO N
TOGROWT HAN DMAINTENANC E INHIGHE RPLANT S
F.W.T.Pennin gd eVrie s
PROEFSCHRIFT
TERVERKRIJGIN GVA ND EGRAA D
VANDOCTO RI ND ELANDBOUWWETENSCHAPPEN ,
OPGEZA GVA ND ERECTO RMAGNIFICUS ,
PROF.DR.IR.H.A . LENIGER,
INHE TOPENBAA RT EVERDEDIGE NO P
VRIJDAG 21DECEMBE R 1973DE SNAMIDDAG SO MVIE RUU R
IND EAUL AVA ND ELANDBOUWHOGESCHOO LT EWAGENINGE N STbLUNJiJt
- I - leerboeken iter plantenfyaiologie beaehrijven p.cvoonlijk bet begrip "fotoajmthete" te eng alt tie venting van koolhydraten uit kooleuur en water ottder invioed van lichl. liet ia beter "fatoeynlheae" ce defi- nieren *U de too van alle ayntheaeproceaeen die onder onvloed van lichc in de groene plant gebeuren, en dan de verachillende onderdeien, te weten de reductieve koolcuuraaaiedlatie, de nitraatreductie en bijbehorende proceaaen, en de ayrtthese van diverae polyeeren, afsoo- derlijk aan te duiden.
(dit proefschrift)
- 2 -
Bijbe t bestuderen van adesrtalinp,va n planten behoort invee l grolerc •ate dan tot nu toe §c«vo«m ia,nadru k tewordc n geleed ophaa r func- tionele karakter.
(dit prf^eCachrIft )
- %- De anelheid van haterotrofc groel van een plant of orgaan Van eenvou- dig en noo deatructiaf worden afgeteid uit stttingen van de adrchalinpa- snelheid. (dit proc(achrift)
- 4 -
Met isnie t aogelijk raasetiva n debelangrijkst e landbouwgewaaaen te kveken die hun aasiailaten efficienter benutten voorbioaynthea e dan dehuidig e rassen.He t iawe l xinvol te zoeken naar planten die lagere onderhoudakoetenhebbe n dan debeataand e planten,o f te proberen een verlaplng van dexe kosten tebewerkstelligen .
(dit proefechrift) - 5-
Voorkandidaatspractic a fysiologiebied the texperimentere nme t simulatiemodellenvaa kgroter emogelijkhede nda nhe tdoe nva n proevenme treel eobjecten .
- 6-
Simulereni sd ebeste ,e ntoc hgoedkop eleidraa dbi jhe tbestudere n vanhe tverloo pva nprocesse nbinne nee nbetrekkelij kafgeslote n geheel,da ti ngrot etrekke nbeken dis .
- 7-
Veelrekencentr a zijnno gnie tingestel do pklante ndi egee nbelan g stelleni nd ewerkwijz eva nd ecomputer .
-8 -
Plantendi ezij nopgegroei d inklimaatkamer sbi jee n lichtintensiteit ____ _2 —— .•- — ———• • vanminde rda n30 0W m zijnongeschik tvoo rhe tbepale nva nd ein - tensiteitva nprocesse nonde rveldomstandigheden .
- 9-
0md egemotiveerdhei dvoo rhe tverlene ne nontvange nva nsteu naa n armelande nt ebevorderen ,i she tnoodzakelij k degeestelijk eafstan d tussenhulpverlenend ee nhulpontvangend egroepe nt everkleinen .Hier - toekunne nhe tuitwissele nva npersone ne nhe tmogelij kmake nva n informatieve,goedkop ereize nbelangrij kbijdragen .
- 10-
Leidinggevendpersonee li sal senzym-eiwi ti nee nlevend eeel :beid e zijnduu ro mt evorme ne nt eonderhouden ,he taanpassingsvermoge nva n deeenhei dwaarto ez ebehore ni smed eafhankelij kva nhu n"turnover" , enwannee rd egroe istilstaa tleid topeenhopin gva ninactiev eelemen - tento tverstarrin ge nsteed sslechte rfunctioneren .
F.W.T.Pennin gd eVrie s Wageningen,2 1decembe r197 3 BEKNOPTESAMENVATTIN GVA NDI TPROEFSCHRIF T
Debetekeni s enregulerin gva nademhalingsprocesse ni n planten zijnbestudeer d omvas t testelle nhoevee lva nd ekool - stofdi edoo r fotosynthese isvastgeieg ddoo rademhalin gwee r verloren gaat.He tgrootst edee lva nd eadenihalin gva nveldge - wasseni she t gevolgva ngroeiprocessen .O p theoretische gronden zijnverbande n tussengroei ,substraatgebrui ke nadem halingnauwkeuri gberekend .Experimentee l zijndez e ookbeves - tigd.Ee nande rdee lva nd eademhalin gword tveroorzaak t door onderhoudsprocessen diecelle n intacthouden .Dez e zijnno g weinigonderzocht .Daardoo ri soo kd egroott eva nd eonderhouds - ademhalingno gnie tprecie sbekend .We ii see ninzich t verkregen ind eprocesse n diehierbi jee nro lspelen . CURRICULUMVITA E
De auteuri sgebore no p2 6maar t 1946 inNijmegen .I n 1963 behaaldehi jdaa rhe tH.B.S.- B diplomaaa nhe tDominicu sCollege , enbego ndaarn ame td eBiologie-studi e aand eKatholiek eUniver - siteit.He thoofdva kplantenfysiologi e is inWageninge nbewerk t onder leidingva ndr.ir .J.F .Bierhuizen .I nmaar t 1969legd ehi j hetdoctoraa lexame na fe ni napri lva nda tjaa r stelded eLand - bouwhogeschoolhe maa nal swetenschappelij kmedewerke rbi jd e AfdelingTheoretisch eTeeltkunde .Hie rwerk thi jme eaa nhe tver - beterene nuitbouwe nva nsimulatiemodelle n overgewasgroei .He t proefschrift overd ebetekeni sva nd eademhalin gva nplante ni s bewerkt onder leidingva nprof.dr.ir .C.T .d eWit ,hoogleraa r ind eTheoretisch e Teeltkunde aand eLandbouwhogeschoo le n prof.dr.A.H .Stouthamer ,hoogleraa r ind eMicrobiologi c aan deVrij eUniversitei t teAmsterdam .D eproeve nbi jdez eonder - zoekingen genomen,zij nuitgevoer d innauw e samenwerkingme t hetInstituu t voorBiologisc h enScheikundi g Onderzoekva n Landbouwgewassen teWageningen . Thisthesi scomprises :
1.A generalINTRODUCTIO N and SUMMARY inENGLIS H (7pages )
2.Ee nalgemen eINLEIDIN G enSAMENVATTIN G inhe t NEDERLANDS (7bladzijden ) and threepapers :
3.PRODUCTS ,REQUIREMENT SAN DEFFICIENC Y OFBIOSYNTHESIS , A QUANTITATIVEAPPROACH .Journa lo fTheoretica l Biology, 1974(i npress ) (51pages )
4.US E OFASSIMILATE S INHIGHE RPLANTS .In :Photosynthesi s andproductivit y indifferen tenvironments .Ed . J.P.Cooper ,Cambridg eUniversit yPress ,197 4(i npress ) (29pages )
5.TH ECOS TO FMAINTENANC EPROCESSE S INPLAN TCELL S Annalso fBotany , 1974 (inpress ) (38pages )
F.W.T.Pennin gd eVrie s
October 1973 SUBSTRATEUTILIZATIO NAN DRESPIRATIO N INRELATIO N
TOGROWT HAN DMAINTENANC E INHIGHE RPLANT S
FiW.T.Pennin gd eVrie s
Departmento fTheoretica lProductio nEcolog y
.Agricultura lUniversity ,Wageninge n
TheNetherland s
Thispape rcontain sa summar y of thereference s3 ,4 an d5 . - 1-
Introduction
Therecen tdevelopmen t of simulation techniques tostud y growtho f fieldcrop sactualize d thequestio nho wmuc ho fth ecarbo n fixedb yphoto synthesis gets lostb y respiratory processes (1).A coheren tpictur e can hardlyb e constructed fromliteratur edat ao ncarbo ndioxid e production andoxyge nconsumptio n ofdifferen t organs invariou s conditions,an d certainlynon etha tallow sextrapolatio n toothe r situations.Thi s study tries toanswe r thisquestio nb y theinvestigatio n ofth esignificanc ean d regulation ofrespirator yprocesse s inplants .Althoug h thisproble mi s focussed tohighe rplant s iti so fa muc hbroade rnature . Five groupso fprocesse swer e recognized inwhic h carbondioxid e evolutionan d oxygenuptak ear e involved:
1.Processe srelate d toth ebiochemica lconversio no f substrate intoth e compounds found inorganisms ,o rshortly :growt hprocesses .Th ecentra l question isho wman y gramso f carbondioxid e areproduce d andho wman y gramso foxyge nar econsume d if 1.0 gramo fglucos e isconverte d into biomass.Th e questionho wman y gramso fbiomas sar e formed simultaneously isclosel yrelated ,bu t theanswe r toth esecon d questiondoe sno t follow from theanswe r toth e firstbecaus eals owate r isinvolved . 2.Processe srelate d tomaintenanc e ofalread y existing cells and their structures.Energ y for theseprocesse s isprovide db yrespiration .Fro m respirationmeasurement s itappear s that theintensit yo fmaintenanc e processes inplant s islo wcompare d toanimal s andmicro-organisms . Inman y situations,however ,thes eprocesse s doconsum e animportan t fractiono fth eassimilates . 3.Processe s related toactiv e transporto forgani ccompound s across cell membranes and inphloe mvessels .Nearl y allsubstrat e forgrowt hi s transportedbecaus e substrateproductio n usually doesno t occuri n growingcells .Watertranspor ti sa passiv eprocess ,whic h active regulationrequire sver y littlerespirator y energy. 4.Processe swithou tuseful l outcome.A considerabl e fractiono f thecarbo n dioxideevolutio n inplant sha softe nbee nascribe d to"uncouple d respiration":a proces swithou t any (known)use .I ti spressuppose d for this study that theseprocesse s areunimportant ,an d thisi s demonstrated ina fewcases .T odecid e that theseprocesse s areals o absent inothe r conditions,simultaneou smeasurement s are lackingo f rateso frespiration ,protei n turnoveran d ionfluxe sacros smembranes . - 2-
5.Photorespiration .Th ecalculatio n ofcarbo ndioxid e assimilationo fa canopy isusuall ybase d onth ecarbo ndioxid e assimilation light respons curveo fa singl e leafi nsimila rconditions .A possibl edecreas eo fth e rateo fassimilatio ndu et ophotorespiratio ni salread y includedi n thiscurve ,an dphotorespiratio ni sno timportan tan ylonge r forsuc h calculations.Becaus ei ngenera lphotosynthesizin g cellsd ono tgro w andnon eo rlittl ephotosynthesi s occursi ngrowin g cells,photorespiratio n doesno tcontribut e toformatio no fan yothe rproduc t thansugar san d aminoacids ,whic h amounti sknow nalready .
Theenerg y consumptioni nothe r activeprocesse s inplant si s negligible. Inthi swa yth einitia lproble mi srestricte d andclarifie d considerably It isno wver y similar totha to fproduction-microbiologists ,bu ti sstil l newfo rman yplan tphysiologists .
Methods
Todetermin e theamoun to fbiomas s formed froma certai n amounto f substratean dth econcomitan trespiration ,th e"reactio nequation "o fth e biochemical conversionsma yb ecalculated .Fo rexample ,i flysin ei sth e endproduc tan dglucos ean dammoni asubstrates ,handbook so fbiochemistr y indicate thati nplant s thisconversio nca nb erepresente db yth ereactio n equation:
1glucos e+ 2 NH L+ 2 NADH 2+ 2 AT P-* 1 lysine + 4 H„0 +2NAD+2ADP+2P.
Heterotrophic cells obtainth ehydroge n (NADH^)an denerg y (ATP)require d byoxidatio no fglucose .Th emaximu mefficienc y ofsubstrat ean denerg y utilizationi salway sused ,s otha t thetota lconversio nprocess ,expresse d ingrams ,i srepresente db yth eequation :
1.000g glucos e+ 0.15 6g NH 3+ 0.03 9g 0 2•* •
0.671g lysin e+ 0.25 5g C0 2+ 0.26 9g H 20
Suchequation s canb emad e foral limportan t conversions.T od os oonl y abasi cknowledg ei srequire d ofth ewel lknow nprocesse s thatar eth e directcaus eo fcarbo ndioxid e formationan doxyge nconsumption .Whe n synthesizing complexproduct s thereactio nequation so fth econstitutin g monomers areadde d according tothei rrelativ e importance,an dcos to f polymerizationar eaccounte d for.I nthi swa ya conversio nreactio nca n -3
alsob econstructe d forsynthesi so fa comple xen dproduct ,suc ha sbiomass . Theequatio n containsonl yweight s ofglucose ,oxygen ,minerals ,th e endproduct ,carbo ndioxid e andwater .I nadditio n theactiv euptak eo f glucose andmineral s requires respiratory energy.Finally ,th ecomputation s wereextende d toinclud eals osom eprocesse s thatrequir e littleenergy . Mucho fth ebasi c information forsuc h calculationsha sbee nobtaine d frommicro-organisms ,bu t itseem scorrec t toconclud e thatdifference s inthi srespec tbetwee nvariou skind so forganism s areunimportant . Theabov ecalculation s canb eapplie d inprincipl e tohighe rplants , becauseheterotrophic ,growin g cells aregenerall y separated fromautotrophi c nongrowin g cells.Th esubstrat e forgrowt hmostl y consistso f sucrose andamin oacids . Costso fmaintenanc eprocesse s arecalculate d fromth eintensit y of theseprocesse s and theirspecifi c costs. The latterconcer nmainl y costs of (re)synthesis andar efairl ywel lknown ,bu t their intensityha sbee n determined only ina fe wcases .Ther ear eals ostil lremarkabl e few measurements ofmaintenanc e respirationi nplants .
Conclusions
A firstquestio ni swhethe r theyiel d of growthprocesse s calculated inthi swa y agreeswit hwha t isfoun di nplants ,o r that iti so fpurel y theoretical value.A simpleexperimen tb yKandle r (2)answer s this.H e grewmaiz eembryo' s indarknes s at2 7C i na petr i diskwit ha nutrien t solutioncontainin g glucose andnitrate ,an ddetermine d theweigh t increase ofth eembryo' s and theamoun to fglucos econsume dove ra fiv eday s period.Oabasi so fa nestimat eo f thecompositio no f thebiomas s synthesized asimplifie d calculation ofho wmuc h glucose isrequire d theoretically for synthesis ismad e (table 1).I nadditio n to6 6m g glucoseneede d for thesynthesi so f47. 5m gdr ymatter ,uptak eo fglucos ean dmineral s consumes theenerg yo f 3.7m g glucose.Maintenanc e of themateria lalread y formedconsume s 2t o5 m g glucose,s otha t thetota lglucos e consumption iscalculate d tob e 71.5t o74. 5m g glucose.Thi s isalmos t identicalt o theexperimenta lresul t (75.4+ 2. 4 mg). Theratio so f thevolume so f carbondioxid ean d oxygen involved inth ecalculatio n (1.35-1.29)an d the experiment (1.2+ 0.1 )als oagre efairl ywell .I t is therefore concluded thatth ereactio nequatio n derived frombasi cbiochemica l datareflect s reality at leastunde r good growing conditions,and thatenzymati c conversions - 4-
and transportprocesse si nplant s occura talmos tmaximu mefficiency . Becauseth ecos to fsynthesi san dtranspor tar eindependen to ftemperature , theresul ti salmos t independent oftemperature .
Table 1.A calculatio no fth eamount so fglucose ,C0 2 and0 „ involved insynthesi so f47. 5m go fmaiz eplan ti ndarkness .Meanin go f thecolumns :(1 )weigh tincreas ei nm go fth efractio nconsidere d (only "total"an d "nitrogenous compounds"hav ebee n observed), (2)amoun to fth efractio nconsidered ,i ng ,forme d from 1.0g o f glucose,(3 )m gglucos erequire d forbiosynthesis ,(4 )amoun to f CO.,i ng ,release d during conversiono f1. 0g o fglucos e into thefractio nconsidered , (5)m gC0 «released , (6)amoun to f0 2, ing ,require d forconversio no f 1.0g glucos e intoth efractio n considered,(7 )m g0 2 required.Th efigure s inth ecolumn s(2) , (4)an d (6)ar estandar dvalues . fractionso fth e (2) (3) (4) (5) (6) (7) biomass formed (0 carbohydrates 32.6 0.826 39.50 0.102 4.02 0.082 3.23 nitrogenous compounds 5.6 0.404 13.85 0.673 9.35 0.174 2.42 organicacid s 3.0 1.104 2.71 -0.050 -0.14 0.298 0.81 lignin 2.4 0.465 5.16 0.292 1.51 0.116 0.60 minerals 2.4 lipids 1.5 0.330 4.54 0.530 2.41 0.116 0.53 total 47.5 — 65.76 — 17.15 — 7.59
A computerprogra mha sbee nformulate d toexecut e thesedetaile d calculations.A sensitivity analysis indicated thatth eroug h chemical compositiono fth een dproduc t (asindicate d intabl e 1),an dth efor m inwhic hnitroge nwa ssupplie d (asnitrat eo rammonia) ,hav e themos t effecto nth eamoun to fbiomas s formedan dth erespiration .Muc h less importantar emor eprecis e datao nth ecompositio no fth een dproduc t (sucha sth eamin oaci dcompositio n ofprotein) ,cellula rcompartmentatio n ofprocesses ,maintenanc e costo fuse denzymes ,an deve nth eefficienc y ofoxidativ ephosphorylatio nbetwee n 100% an d5 0% o fit smaxima lvalu e iso fmino r importance.Consequentl y asimplifie d schemewa sderive d tocalculat e thereactio nequatio no fconversion s(3) . Theabov ecalculation snee dno tmuc h changei fapplie d toautotrophi c plants:onl y thesynthesi so fman ynitrogenou s compounds consumes amino - 5-
acidsan d sucroseinstea d ofglucos ean dminerals ,an d costo f active transportha s tob e included.Th e transportcos t for translocationove r shortdistance s isprobabl ymainl y thato fpassin gmembrane s of thecel l andphloe mvessels ,bu t transportove rman ymeter sma yb emuc hmor e expensive.Ther e isals oa nimportan t difference:i nmos t agricultural crops themajorit y ofnitrat ereductio n occurs inth e leaves inth elight . If the light intensity isi nth eligh tsaturate dpar to f thecarbo ndioxid e assimilation lightrespon s curve,th erat eo f carbondioxid e assimilation is limitedb y therat eo f carbondioxid e diffusionint oth e leaf,an d because thenmor eenerg y isavailabl e inth egree ncel ldu e toth ehig h light intensity theothe renerg y requiringprocesse s dono tdecreas e thecarbo n dioxideassimilation .Thi s isimportan tespeciall y fora nexpensiv eproces s sucha snitrat e reduction.Fo r thisreaso nnitrat e reduction infiel dcrop s consumesmuc h lessenerg yfro massimilate s thani sexpecte d fromit shig h reduction costi ndarkness .Als oothe rprocesse s canus eenerg y thatha s notbee n fixed inassimilates ,bu t thesear eusuall y lessimportant .Mainl y due tonitrat ereductio nenerg y absorptionb y leaves isofte n5 t o 15% highe i thani sexpecte daccordin g toth ereaction :carbo ndioxid eplu swate rplu s lightenerg y gives glucoseplu soxyge n(4) . Since formation ofbiomas s fromassimilate s causes apredictabl e carbondioxid eproduction ,i ti spossibl e todetermin eno ndestructivel y therat eo fgrowt hb ymeasurin g therat eo frespiration .Thi s isconfirme d byexperiment s inwhic hsubstrat e utilization,respiratio nan d growtho f wholeplant s isknown ,a sfo rexampl e inconstan t conditions inth elight , where therate so fcarbo ndioxid e assimilationan d of growth (and therefore thato fdissimilation )ar erelated .A compariso no fmeasure d and calculated ratioso f assimilation todissimilatio no fyoun gplant so fvariou s species atsom e temperatures demonstrates that also theseplant sutiliz e their substratesa t thebiochemicall y maximalefficienc y (4).I tseem s thus impossible toincreas e theefficienc y ofplant s inthi s senceb yplan t breeding. Maintenanceprocesse s requirea nunimportan tamoun to fenerg y in rapidlygrowin g tissues,i.e .a ta relativ egrowt h rateo f0. 3 gg day" ormore ,bu ta considerabl e fraction inothe rcase s (3,5).Measurement s ofmaintenanc e respiration indicate that theseprocesse s consumeabou t 1t o4 % o f theweigh to f thedr ymatte r in thefor mo f carbohydrates per day.Knowledg e ofth eindividua lmaintenanc eprocesse s indicates that themai npar t ofi ti suse d forcontinuou sbreakdow n andresynthesi so f - 6-
proteins,whil eanothe r important fraction isrequire d tomaintai n ion concentrations incells .T odetermin e theamoun t ofsubstrat e required from thecalculate d energy consumption inthes eprocesse s iti sessentia l tokno w theefficienc y ofoxidativ ephosphorylation .However ,du et o technicaldifficultie s this information is stillver y limited inplants . The intensity ofprotei n turnover,an d therefore its cost,probabl y dependso nth emetaboli cactivit y of thecells ,whic hma yb e expresseda s thedail ycarbo ndioxid e assimilation.Th ecos t ofmaintainin g ion concentrations dependsmainl y upon theenvironment .Th efirs t conclusion arisesmainl y frommeasurement so f themaintenanc e respirationrat e in leaves,an d thefe wbasi cdat ad ono tsuppor to roppos e this.Th e second conclusion isderive dmainl y frombasi cdat aan dwa sonl y indirectly confirmed. Itseem sworthwhil e toinvestigat eho w toreduc eprotei n turnover,a proces s thatma yhav e lostmuc ho fit s importance inpresen t agricultural conditions.Unlik e increasing theefficienc y of synthetic processes inplants ,whic h isconsidere d tob e impossible,i tseem s feasible tocontro l therat eo fmaintenanc e processes,an d thust o influence thecro pyiel dconsiderabl y (5).Cos to fmaintenanc e processes probably depend onexterna l conditions,suc ha stemperature ,salinit y and waterstress ,bu t this cannotb equantifie d asyet . Manymino rquestion shav eno tbee nanswere dbecaus e of lacko fbasi c data.Probabl ybecaus e therat eo f syntheticprocesse s inth e investigated organi sunknown ,quit e someunexplaine d observations remain also.I ti s likely thatman yo fsuc hobservation swil lno tb eexplaine dbefor ea better insighti sobtaine d into theprocesse s andfactor s thatstart , regulatean d influencebiochemica lconversion s andtransport .
Literature
1.D eWit ,C.T. ,R .Brouwe ran dF.W.T .Pennin gd eVries ,1970 :Th e simulation ofphotosyntheti c systems.In :Predictio nan dmeasuremen t ofphoto - syntheticproductivity .Pudoc ,Wageningen ,Th eNetherlands . 2.Kandler ,0. , 1953:Uebe r den "SynthetischenWirkungsgrad " invitr o cultivierter Embryonen,Wurzel n andSprosse .Z .Naturforschg .8b , 109-117. 3.Pennin gd eVries ,F.W.T. ,A.H.M .Brunstin g andH.H .va nLaar ,1974 : Products,requirement s andefficienc y ofbiosynthesis .A quantitative approach.J . Theoret.Biol. ,i npress . - 7-
4.Pennin g deVries ,F.W.T. , 1974a:Us eo fassimilate s inhighe rplants , In:Photosynthesi s andproductivit y indifferen tenvironments . Ed.J.P .Cooper ,Cambridg eUniversit y Press,i npress . 5.Pennin g deVries ,F.W.T. , 1974b:Th ecos to fmaintenanc e processes inplan tcells .Ann .Bot. ,i npress . SUBSTRAATBENUTTINGE NADEMHALIN GI NVERBAN DME T
GROEIE NONDERHOU DI NHOGER EPLANTE N
F.W.T.Pennin gd eVries i
Vakgroep TheoretischeTeeltkund e
•Landbouwhogeschool ,Wageninge n
Ditgeschrif ti see nsamenvattin gva n de literatuurverwijzingen3 ,4 e n5 . -1
Inleiding
Derecent eontwikkelin gva nsimulatiemethodieke nvoo rhe t bestuderen vand egroe iva nt eveld estaand egewasse nactualiseerd ed evraa ghoevee l vandoo rfotosynthes evastgelegd ekoolsto fverlore n gaatdoo rademhalings - processen (1). Uit literatuurgegevens overkoolzuurafgift e enzuurstof - opnameva nverschillend eorgane ni ndivers eomstandighede nka nnauwelijk s eensamenhangen dbeel dworde nverkregen ,e nzeke rgee nbeel dda textrapo - latiesnaa rander esituatie s toelaat.I ndez estudi e isgepoog d deboven - staandevraa g tebeantwoorde ndoo ronderzoe knaa rd ebetekeni s enregu - leringva nademhalingsprocesse n inplanten .Koewe ld evraagstellin g is toegespitst opplante ni ndez ei nweze nbrede re nva n toepassingo pall e organismen. Deprocesse nwaarbi jkoolzuurgasvormin ge nzuurstofopnam ezij nbetrok - ken zijni nvij f groepent eonderscheiden :
1.Processe ndi esamenhange nme td ebiochemisch eomzettinge nva n substraat ind everbindinge ndi ei norganisme nworde naangetroffen ,o fkortweg : groeiprocessen.D ekernvraa g ishie rhoevee lgra mkoolzuu re rvrijkom t enhoevee l gram zuurstofe rword topgenome nwannee r 1.0 gramglucos e wordtomgeze ti nbiomassa .D evraa ghoevee lgra mbiomass ahierbi jword t gevormd houdthierme enau wverband ,maa rhe tantwoor d opd e tweedevraa g volgtnie tui the tantwoor d opd eeerst eomda too kwate rbi j dereactie s isbetrokken . 2.Processe ndi esamenhange nme the ti nstan dhoude nva nreed sbestaand e cellene nhu nstructuren .D eenergi evoo rdez eactiev eprocesse nword t doorademhalin ggeleverd .Ui tademhalingsmetinge nblijk tda td einten - siteitva nonderhoudsprocesse ni nplante n laagi svergeleke nbi j dieren enmicro-organismen ,maa r invee lsituatie sconsumere ndez eprocesse n tochee nbelangrij kdee lva nd eassimilaten . 3.Processe ndi everbonde n zijnme tactie fvervoe rva norganisch everbin dingendoo rcelmembrane ne ni nd evaatbundels .Vrijwe lall esubstraa t voor groeiword t getransporteerd,omda tsubstraatprodukti emeesta lnie t plaatsvindt ingroeiend ecellen .Watertranspor ti see npassie fgebeuren , waarvand eactiev eregulerin g uiterstweini g ademhalingsenergievergt . A.Processe ndi egee nnutti gresultaa tafwerpen .Herhaaldelij k isgesugge - reerdda tee naanzienlijk e fractieva nd ekoolzuurontwikkelin g inplan - tenmoe tworde ntoegeschreve naa n"ontkoppeld eademhaling" :ee nproce s zondereni g (herkenbaar)nut .Ee nuitgangspun t voordez estudi ewa sda t - 2
dergelijkeprocesse nnie tva nbelan g zijn,hetgee n inenkel e gevallen ookwer daangetoond .He t isno gonzeke ro fdez eprocesse nnooi toptreden , maaro mdi tvas t testelle nontbreke nvooralsno ggelijktijdig ewaar - nemingenva nademhalingssnelheden ,va neiwitturnove re nva n ionfluxen doorcelmembranen . 5.Fotorespiratie .He ti sgebruikelij k omd ekoolzuurassimilati eva nee n gewas teberekene nme t dekoolzuurassimilatie-licht-respons-curv e vanee nbla d inovereenkomstig eomstandigheden .Ee neventuel everlagin g vand eassirailatie-snelhei ddoo r fotorespiratie isda na li ndez ecurv e verrekend,e nfotorespirati e isdu snie tmee rva nbelan gvoo rzulk e berekeningen.Omda ti nhe talgemee nfotosynthetiserend e cellennie tmee r groeien,e ni ngroeiend ecelle ngee no fweini gfotosynthes eplaatsvindt , levertfotorespirati e geenbijdrag e totd evormin gva nander eprodukte n dand ereed sbekend ehoeveelhei d suikerse naminozuren .
Inplante nvrage nd eander eactiev eprocesse nee nt everwaarloze n hoeveelheid ademhalingsenergie. Hetaanvankelijk eproblee mi sdaarme eaanzienlij k ingeperkte nver - duidelijkt.He tkom tn uster k overeenme tda tva nproduktie-microbiologen , maar isno gnieu wvoo rvee lplantenfysiologen .
Werkwijze
Hetvaststelle nva nd ehoeveelhei dbiomass adi ei nee ngroeiproce s kanworde ngevorm dva nee nzeker ehoeveelhei d substraat,e nd egroott eva n debijbehorend egaswisseling ,ka ngebeure ndoo rhe tberekene nva nd e "reactievergelijking"va nd ebiochemisch e omzettingen.Wanneer ,bijvoorbeeld , hetaminozuu r lysinehe teindproduk t ise nglucos ee nammonia khe tsubstraat , blijktui tbiochemie-handboeke n datdez eomzettin g inplantencelle nka n wordenweergegeve nme td e reactievergelijking:
1glucos e+ 2 NH ~+ 2 NAIffl L+ 2AT P-» • 1lysin e+ 4 H 0+ 2NA D+ 2 AD P+ 2 P . o 2 i
Heterotrofecelle nverkrijge nd ebenodigd ewatersto f (NADH2)e nenergi e (ATP)doo rglucos e teverbranden .Bi jall eomzettinge n issteed sd egroots t bekendegraa dva nbenuttin gva nsubstraa te nenergi eaangehouden ,zoda t hetgehel eomzettingsproces ,uitgedruk t ingrammen ,word tweergegeve n - 3-
doord evergelijking :
1.000g glucos e+ 0.15 6g NH. ,+ 0.03 9g 0 _•>
0.671g lysin e+ 0.25 5g C0 2 +0.26 9g H 20
Dergelijkevergelijkinge nkunne nworde nopgestel dvoo rall ebelangrijk e omzettingen.Va nd eprocesse ndi ed eonmiddellijk eoorzaa k zijnva n koolzuurafgiftee nzuurstofopname ,e ndi edoo r diepgaand onderzoek goed bekend zijn,i sdaarbi jslecht selementair ekenni svereist .Bi jd e syntheseva nsamengesteld eeindprodukte nworde nd ereactievergelijkinge n vand econstituerend emonomere ngewoge nopgeteld ,e npolymerisatiekoste n inrekenin g gebracht.Oo kvoo r syntheseva nee ngecompliceer deindprodukt , zoalsbiomassa ,word to pdez ewijz eee nreactievergelijkin g vastgesteld, metal senig e termend egewichte nva nglucose ,zuurstof ,mineralen ,he t eindprodukt,koolzuurga se nwater .Daarenbove nvraag the tactiev eopneme n vanglucos ee nminerale nui the tmediu mademhalingsenergie .D eberekeninge n zijntenslott everfijn ddoorda too kme tweini genergi evragend eprocesse n rekeningi sgehouden . Veelva nd ebenodigd ebasisinformati ei sverkrege nme tbehul pva n micro-organismen,maa rd econclusi e lijktgewettig d datdez enie tbelangrij k afwijkti nverschillend e soortenorganismen . Bovenstaandeberekeninge nkunne ni nbeginse longewijzig dworde ntoe - gepasti nhoger eplahten ,omda tal srege lheterotrofe ,groeiend e cellen gescheidenzij nva nautotrofe ,nie t groeiendecellen .He tsubstraa tvoo r groeibestaa tda nmeesta lui tsucros ee naminozuren . Deberekenin gva nd ekoste nva nonderhoudsprocesse n geschiedto p basisva nintensitei tva ndez eprocesse ne nhu nspecifiek ekosten. " Deze laatstebetreffe nvoornamelij kkoste nva n(her)synthes ee nzij n redelijk goedbekend ,maa rhu nintensitei ti sno gi nweini g gevallen vastgesteld.Oo kzij ne rno gopvallen dweini g goedemetinge nva nd e onderhoudsademhaling inplanten .
Conclusies
Eeneerst evraa gi so fd ealdu sberekend eopbrengs tva ngroeiprocesse n overeenkomtme twa tgevonde nword ti nplanten ,o fda the tee npuu r theo- retischmaximu mis .Ee neenvoudig eproe fva nKandle r (2)geef thierove r uitsluitsel.Hi jlie tmaisembryo' so pee npetrischaa lme tee nsteriel e voedingsoplossingme tglucos ee nnitraa t groeieni nhe tdonke rbi j27°C , enbepaald ed egewichtstoenam eva nd eembryo' se nd eopgenome n hoeveelheid - 4-
glucoseove ree nperiod eva nvij fdagen .O pbasi sva nee nz ogoe dtnogelijk e schattingva nd esamenstellin gva nd egevormd edrog esto fi see nvereen - voudigdeberekenin g gemaaktva nd eglucos edi etheoretisc hnodi gi svoo r synthese (tabel1) .
Tabel1 Eenberekenin gva nd ehoeveelhede nglucose ,0 „e nCO -di e betrokken zijnbi jsynthes eva n47. 5m gmaisplan ti nhe tdonker . Betekenisva nd ekolommen : (1)gewichtstoenam ei nm gi nd ebe - treffende fractie (alleen "totaal"e n"stikstofhoudend ever - bindingen"zij nwaargenomen) , (2)aanta lg va nd ebetreffend e fractieda tword tgevorm dui t1. 0g glucose ,(3 )aanta lm g glucosenodi gvoo rbiosynthese ,(4 )aanta lg C0 »da tvrijkom t bijd eomzettin gva n1. 0g glucos ei nd ebetrefrend efractie , (5)aanta lm gCO _ datvrijkomt ,(6 )aanta lg 0 „da tnodi gi s bijd eomzettin gva n1. 0g glucos ei nd ebetrexfend efractie , (7)aanta lm g0 „da tnodi gis .D egetalle ni nd ekolomme n(2) , (4)e n(6 )zij nstandaar dwaarden .
fractiesva nd e (3) (4) (5) (6) (7) gevormdebiomass a (1) (2)
koolhydraten 32.6 0.826 39.50 0.102 4.02 0.082 3.23 stik stofhoudend e 5.6 0.404 13.85 0.673 9.35 0.174 2.42 verbindingen organischezure n 3.0 1.104 2.71 -0.050 -0.14 0.298 0.81 lignine 2.4 0.465 5.16 0.292 1.51 0.116 0.60 mineralen 2.4 — — — — — — lipiden 1.5 0.330 4.54 0.530 2.41 0.116 0.53
totaal 47.5 — 65.76 — 17.15 — 7.59
Behalveongevee r6 6m gglucos edi enodi g zijnvoo rd esynthes eva n 47.5m gdrog estof ,vereise nd eopnam eva nglucos ee nminerale nd eenergi e van3. 7m gglucose .Voo ronderhou dva nhe treed sgevormd emateriaa li s 2 tot5 m gglucos enodig ,zoda tdetotal eglucose-consumpti evolgen sbere kening71. 5to t74. 5m gbedraagt .Di ti snagenoe g identiekme thetgee n experimentedwa svastgestel d (75.4+ 2. 4mg) .D everhoudin g tussend e betrokkenvolumin akoolzuurga se nzuursto f ind eberekenin g (1.29- 1.35) end emetin g (1.2+ 0.1 )stemme noo kvri jgoe dovereen .Blijkbaa rweer - spiegeltd eva nbasisgegeven s afgeleideomzettingsvergelijkin gtenminst e ondergoed egroeiomstandighede nd ewerkelijkheid ,e nverlope n enzymatische omzettingene ntransportprocesse n inplante nvrijwe lmaximaa lefficient . - 5-
Omdatd ekoste nvoo rsynthes ee ntranspor tnie tva nd e temperatuuraf - hangeni sdi tresultaa t ookbijn aonafhankelij kva nd etemperatuur . De gedetailleerdeberekeninge nworde nuitgevoer d dooree ncomputer - programma.Ui tee ngevoeligheidsanalys eblee kda td egrov echemisch e samenstellingva nhe teindproduk t (zoalsi ntabe l 1aangegeven )e nd e vormwaari n stikstofword t aangeboden (alsnitraa to fal sammoniak )d e meesteinvloe dhebbe no pd egevormd ehoeveelhei dbiomass ae nd egaswisse - ling.Va nvee lminde rbelan g zijnee nverder epreciserin g vand esamen - stellingva nhe teindproduk t (zoalsd eaminozuursamenstellin gva n eiwit), decellulair ecompartimentati eva nprocessen ,d eonderhoudskoste nva n gebruikteenzyraen ,e nzelf sd eefficienti eva noxidatiev e fosforylering tussen 100% e n5 0% va n zijnmaximal ewaarde .Ee n sterkvereenvoudig d schemao md ereactie-vergelijkinge n vanomzettinge nt eberekene nwer ddaar - omafgelei d(3) . Bovenstaandeberekeninge n zijnvrijwe longewijzig d geldigvoo r autotrofeplanten :allee n syntheseva nvee lstikstofhoudend everbindinge n gebeurtva naminozure n ensucros e inplaat sva nglucos ee raineralen,n en dekoste nva nactie f transportmoete nworde nverreken d (3,4).Bi jvervoe r overkort eafstande n zijntransportkoste nwaarschijnlij k vooraldi eva n hetpassere nva nd emembrane nva ncel ~e nvaatbundel ,maa rhe t isno gnie t uitgemaakt oftranspor t overvel emeter snie tvee lduurde r is.E ri s echteroo kee nbelangrij k verschil:i nd emeest e landbouwgewassenvind t hetovergrot edee lva nd enitraatreducti eplaat s ind ebladere n inhe t licht.Wannee rd e lichtintensiteit inhe t lichtverzadigde deelva nd e koolzuurassimilatie-licht-respons-curveis ,word td ekoolzuurassimilatie - snelheidbepaal d doord esnelhei dwaarme ekoolzuurga she tbla di n diffundeert,e nomda tdoo rhe tvel e lichtda nno gmee renergi e degroen e eelte rbeschikkin g staat,verlope nd eander eenergie-vragend e processen niette nkost eva nd ekoolzuurassimilatie .Me tnam evoo ree nduu rproce s alsnitraatreducti e isdi tee nbelangrij k gegeven.O mdez erede nvraag t nitraatreductie inlandbouwgewasse nbeduiden dminde renergi eva nassimi - latenda no pgron dva nd ehog e reductiekosten inhe t donker zouworde n verwacht.Oo kander eprocesse nkunne nnie t inassimilate nvastgelegd e energiebenutten ,maa r zijnvaa kminde rbelangrijk .Voora l doornitraat reductie isd eenergieabsorpti eva nbladere ndikwijl s5 to t 15% hoge r danword tverwach tvolgen sd ereactie :koolzuurga splu swate rplu s stralingsenergie geeftglucos eplu s zuurstof(4) . - 6-
Omdatvormin gva nbiomass ava nassimilate nee nvoorspelbar ekoolzuur - ontwikkelingveroorzaak t ishe tmogelij kd egroeisnelhei d non-destructief vast testelle ndoo rd eademhalingssnelhei d temeten .Di tword tbevestig d doorproeve nwaari nhe tsubstraatverbruik ,d eademhalin ge nd e groeiva n geheleplante nbeken d is.Di t ishe tgeva li nconstant e omstandighedeni n het licht,waa r desnelhede nva nkoolzuurassimilati ee nva ngroe i (endu s dieva ndissimilatie )o pelkaa r zijnafgesteld .Ee nvergelijkin gva n gemetene nberekend everhoudin gtusse nassimilati ee ndissimilati eva njong e plantenva nverschillend e soortenbi jenig e temperaturen toontda too k dezehu nsubstraa tme td ebiochemisc hmaximal eefficienti ebenutte n(4) . Het lijktda noo knie tmogelij ko mdoo rveredelingswer k deefficienti eva n planten indez e zint everhogen . Onderhoudsprocessen vragenee nrelatie fonaanzienlijk ehoeveelhei d energie insne lgroeiend eweefsels ,di tis :bi jee nrelatiev e groeisnelheid van0. 3 gg dag ofmeer ,maa ree ngeenszin s teverwaarloze nhoeveelhei d inander e gevallen (3,5).Admehalingsmetinge nwijze nui tda tdez eprocesse n dagelijks ongeveer 1to t4 % va nhe tdrog esto fgewich taa nkoolhydrate n consumeren.D eno g geringekenni s vand eindividual e onderhoudsprocessen duidtero pda the t grootste deelhierva n gebruiktword tvoo r voortdurende afbraake nopbou wva neiwitten ,e nda tee nande rbelangrij k deelnodi gi s omionenconcentratie s ind e cellen tehandhaven .0 mui tberekend eenergie - kostenva ndez eprocesse nd esubstraatkoste nvas t testelle ni skenni s van deefficienti eva noxidatiev e fosforylering essentieel,maa rvoo rplante n isdez edoo r technischemoeilijkhede nno gbeperkt . De intensiteitva newitturnover ,e ndu sd ekoste nva ndi tproces ,hang t vermoedelijkvoo ree n grootdee lsame nme td emetabolisch eactivitei tva n decellen ,bijvoorbeel d uitgedrukt alsd edagelijks ekoolzuurassimilatie . Dekoste nva nhe thandhave nva n ionenconcentraties hangenvoora la fva nhe t milieu.D eeerst econclusi evolg tvoorn^amelij kui tmetinge nva nd einten siteitva nonderhoudsademhalin gi nbladeren ,e nword tdoo rd eweinig ebasis - gegevensnie tondersteun d of tegengesproken;d e tweede conclusievolg tvoora l uitd ebasisgegeven s enword t slechtsindirec tbevestigd .He t lijkt zinvol onderzoekt everrichte nnaa rhe treducere nva neiwitturnover ,wel kproce s onderd ehuidig e landbouwomstandigheden mogelijkvee l inbetekeni s heeft ingeboet.I ntegenstellin g tothe tonmogelij k geachteverhoge nva n deefficienti eva nsyntheseprocesse n lijkene rnamelij kwe lmogelijkhede n aanwezigo md esnelhei d vanonderhoudsprocesse n tebeheersen ,e n zod e opbrengstva nhe tgewa sbelangrij kt ebeinvloede n (5).He t iswaarschijn - lijkda td ekoste nva nonderhoudsprocesse n afhankelijk zijnva nuitwendig e omstandighedenzoal stemperatuur ,zoutgehalt eva nd ebode me nwaterspan - ning,hoewe lhierove rno gnie tvoldoend e gegevensbeschikbaa r zijno m dezemenin g tekwantificeren . Vanzelfsprekend zijnno gvee ldetailvrage n onbeantwoordbi jgebre k aanbasisgegevens .Oo k zijne rno ghee lwa t onverklaardemeetresultaten , vermoedelijkvoora lomda td eintensitei tva nsyntheseprocesse n inhe ton - derzochteorgaa nvaa konopgemerk tblijft .He t lijktdaaro mwaarschijnlij k datvee lwaarneminge nva nademhalingssnelhede nnie tvolledi gkunne nworde n verklaard voor eenbete r inzichti sverkrege ni nd eprocesse ne nfaktore n diebiochemisch eomzettinge ne ntranspor ti ngan g zetten,regulere ne n beinvloeden.
Literatuur
1.D eWit ,C.T. ,R .Brouwe ran dF.W.T .Pennin gd eVries ,1970 :Th e simulation ofphotosyntheti c systems.In :Predictio nan d measurement ofphotosyntheti cproductivity .Pudoc ,Wageningen ,Th eNetherlands . 2.Kandler ,0. , 1953:Uebe rde n"Synthetische nWirkungsgrad " invitr o cultivierterEmbryonen ,Wurzel nun dSprosse .Z .Naturforschg .8b , 109-117. 3.Pennin g deVries ,F.W.T. ,A.H.M .Brunstin g andH.H .va nLaar ,1974 : Products,requirement s andefficienc y ofbiosynthetis .A quantitative approach.J .Theoret .Biol. ,i npress . 4.Pennin gd eVries ,F.W.T. , 1974a:Us eo fassimilate s inhighe rplants . In:Photosynthesi s andproductivit y indifferen tenvironments . Ed.J.P .Cooper ,Cambridg eUniversit y Press,i npress . 5.Pennin g deVries ,F.W.T. , 1974b:Th ecos to fmaintenanc eprocesse s in plantcells .Ann .Bot. ,i npress . PRODUCTS,REQUIREMENT SAN DEFFICIENC YO FBIOSYNTHESI S
A quantitative approach
F.W.T.Pennin g deVries ,A.H.M .Brunstin g andH.H .va nLaa r
Department ofTheoretica lProductio nEcolog y
AgriculturalUniversity ,Wageninge n
TheNetherland s
ReceivedMarc h 9, 1973;accepte d forpublicatio n inJourna lo f TheoreticalBiolog y CONTENTS
Summary 1
1.Introductio n 2
2.Shor trevie wo frelate dstudie s 3
3.Som egenera lconsideration s aboutbiosynthesi s 6 3.1.Th ereactio nbalanc efo rsynthesi so fmonomer s 9 3.2.Inorgani cmolecule s 10 3.3.Synthesi s ofpolymer san d formationo f cellularstructure s 11 3.3.1.Polymerizatio n 11 3.3.2.Too lmaintenanc e 11 3.3.3.Biomas ssynthesi s frompolymer s 13 3.4.No nsyntheti c activitiesdurin gbiosynthesi s 14
4.Variable s characterizingbiosynthesi s 15
5.Modification s ofvariable scharacterizin ga biosyntheti c process inducedb y changes incondition s 19 5.1.Compartmentatio n 20 5.2.Alternativ epathway s 21 5.3.Effec to f theP/ 0 ratioo npv ,cp fan dor f 22 5.4.Temperatur e andothe renvironmenta l factors 23
6.Maintenanc e ofcellula r structures andothe r
respirationprocesse s 24
7.Conclusion s 24
8.Reference s 27 PRODUCTS,REQUIREMENT SAM DEFFICIENC Y OFBIOSYNTHESI S
A quantitative approach
1) 2) 3) F.W.T.Pennin gd eVrie s ,A.H.M .Brunstin g andH.H .va nLaa r
Departmento f TheoreticalProductio nEcology ,Agricultura lUniversit y Wageningen,Th eNetherland s
SUMMARY
Thequestio no fho wman y gramso fa norganis mca ngro wheterotrophicall y fromonl y 1.0 gramo f glucosean dadequat emineral sha sbee npu t forward many times.Onl y afe wattempt shav ebee nmad e toanswe r thisquestio n theoretically andthes eattempt swer e ratherrough .I n thispaper ,i t isdem onstrated that theyiel d ofa growt hproces sma yb e accurately computedb y considering therelevan tbiochemistr y ofconversio nreaction s andth e cytologicalimplication so fbiosynthesi s andgrowth .Oxyge nconsumptio nan d carbondioxid eproductio nb y theseprocesse s areals ocomputed .Th eweigh t ofth ebiomas s synthesized from 1.0gra mo f substratean d thequantitie so f gasesexchange d areindependen t oftemperature . Theseresult s areobtaine db y adding theindividua lequation s describing theformatio no feac hcompoun d synthesizedb y theorganis mfro mth esubstrat e supplied.Th esu mrepresent s anequatio nwhic h accounts foral lsubstrat e molecules required forbiosynthesi so f thecarbo nskeleton so fa nend-product , whosechemica lcompositio n isgiven .I ti s thencalculate dho wmuc henerg y isrequire d forth enon-syntheti cprocesse swhic h forma par to fbiosynthesis , sucha sintra -an d intercellulartranspor to fmolecule s andmaintenanc eo f RNAan denzymes .Th eadditiona lamoun to fsubstrat e required toprovid e thisenerg yb y combustioni seasil ycalculated .Addin g thissubstrat e to theamoun tuse dfo rskeleto n synthesis gives anoveral lequatio nwhic h quantifies thesubstrat ean doxyge ndeman da swel la scarbo ndioxid e evolutiondurin gbiosynthesi s of 1.0 grambiomass .Fo rexample ,i trequire s 1.34 gramo f glucosewit h adequateammoni aan dmineral s tosynthesiz e 1.0 grammaiz eplan tbiomas s indarkness ;durin g thisproces s0.1 4 gramoxyge n
1)Partia lfulfillmen t ofa Ph.D .thesi so f thesenio r author 2)Doctorat estuden ti n196 9 3)Technica lassistan t - 2-
areconsume d and0.2 4 gramcarbo ndioxid ear eproduced .I tha sbee n describedelsewher etha tsimila rresult swer eobtaine d experimentallywit h growingplants . Suchresult sdepen dconsiderabl y uponth echemica lcompositio no fth e biomassbein gsynthesize dan dupo nth estat e(oxidize d orreduced )o fth e nitrogensource .Othe rparameters ,suc ha sth enumbe ro fAT Pmolecule s required forprotei nsynthesis ,th epossibilit y forutilizatio no f alternativepathway sfo rsynthesi so renerg yproduction ,th epresenc eo r absenceo fcompartmentatio no fsyntheti cprocesse san dvariation s inth e P/0rati obetwee n 2an d3 ,unde rman ycondition s affectresult s ofth e computation lesstha n 10% . Sincemaintenanc eo fcellula rstructure s isno tconsidered , the approachconcern s thegros syiel do fbiosynthesis .I tpredict s therefore thedr ymatte ryiel d ofheterotrophi c cells froma give nquantit yo f substratea thig hrelativ e growthrates .
1.INTRODUCTIO N
Whatdetermine s theactua lefficienc yo fconversio no fsubstrat e into biomassb y livingorganism s and themaxima lefficienc y underoptima l growth conditions isa proble mwhic hha sattracte dmuc hattention .I ti sa challengingquestio nfo rmicrobiologist s and zoologists since theyar eofte n confrontedwit hsubstrate-yiel d relationships.Man y simultaneousmeasurement s ofgrowt han d substrateconsumptio nhav ebee nmade ,wit h resultsexpresse d inweigh tan denerg yunits .Th ehighes tefficiencie s reported areabou t 30% t o7 0% o na weigh tbasis ,an d slightlyhighe ro na nenerg ybasis . Onemigh tals o try tocalculat e theefficienc y ofa nanaboli cprocess . Thepathway sb ywhic hsubstrat emolecule s areconverte dint oth evariet y of end-productmolecule s foundi ncell s aredescribe d inman y textbooks,an d theamount so fenerg yrequire d for theseconversion s and forpolymerizatio n areknown .Informatio ni sbecomin g availableo n theenergetic s of cytological aspectso fbiosynthesis ,suc ha sactiv e transportacros smembrane san d maintenanceo fth etool sfo rbiosynthesi s (nucleicacid s andenzymes) .Th e substraterequiremen t toprovid e therespirator y energy for these activities canb ecalculated .Th esu mo fth eamount so f substrate formateria lan d forenerg y represents thetota lsubstrat erequiremen t forbiosynthesi s of anend-product .Th etota lo f thesebiochemica lan dcellula rprocesse swil l becalle dbiosynthesi s inthi spaper . - 3-
Tosimplif yth eproble mo fho wt ocalculat e theyiel d ofbiosyntheti c processes,onl y thequantitativ e relationbetwee nsubstrat e anden dproduc t iso finterest ,rathe r thanth eexac twa y inwhic h theen dproduc ti s obtained.Thus ,orde ran drat eo findividua lreaction s areno timportant . Iti sa legitimat esimplificatio ni fth erat eo fa biochemica l reaction doesno tchang eth estoichiometr yo fit schemica lreactio nequatio no rtha t ofothers ,whic h seems tob e generally agreed inbiochemistry . Stimulation ofsynthesi so fproduc tA b ysynthesi so fproduc tB doe sno tdistur b the calculations:the nth een dproduct ,whos echemica lcompositio nmus tb e established experimentally inal lcases ,wil lcontai nmor eo fproduc tA . Energy consumption forth emaintenanc eo f cellstructure s interferes withdr ymatte rproduction .A nestimat eo f thesubstrat e requirementfo r maintenanceprocesse s inplan t cells isgive ni nanothe rpape r (Penningd e Vries, 1974b).Th eter m "growth"wil lb euse d toindicat ebiosynthesi s accompaniedb ymaintenanc e of cellstructures ,an d corresponds todr yweigh t increase. Thepresen tpape rdeal swit h the theoreticalderivatio n frombiochemica l datao fth ereactio nbalanc e forconversio no fsubstrat e intoa particula r product,an dwit h thedeterminatio no fvalue scharacterizin g this conversion process.Suc hvalue sar e theweigh to f thedr ymatte r synthesized from 1.0 gramo fsubstrat ean d theweigh to f thecorrespondin g oxygenuptak ean d carbondioxid eproduction .Thi s studyi sfocusse do nhighe rplants, o fwhic h cellsgro wheterotrophicall y under aerobicconditions .Thi sapplie s toman y situations,sinceeve ni nlea fcell softe nmuc h growthoccur sbefor eth e cellsobtai n thecapacit y tophotosynthesize .Synthesi s oforgani cmateria l fromglucos ei sconsidere d indetail ,bu t thesam eapproac h canb euse dwit h avariet yo fsubstrates .Th eeffec to funfavorabl e conditions forbiosynthesis , sucha sextrem e temperatures,wate rstres so rminera l shortage,ar eno t considered.
2.SHOR TREVIE WO FRELATE DSTUDIE S
The firststudie sabou t thequantitativ e relationbetwee n drymatte r productionan dsubstrat econsumptio nwer eperforme db yPasteu r around 1875, byPfeffe r around 1890an db yRubne r (1904).The yemphasize d theenerg y efficiency ofgrowth .I nth eninetee n twenties and thirtiesth e relationship betweendr ymatte ryiel dan d theamount so f substrate consumedwa s investigated infungi .Tamiy a(1932 )demonstrate d thatth ehea to f combustion ofth esubstrat ei sno ta majo r determinant ofyield : theyiel d expressed 4 -
ing organism spe runi to fchemica lenerg ypresen ti nth e snbstrnt-Pprove d tob evariable .
From the "molecular formula"o ffungi ,C 0/.H,- „ 0,c N,,Tamiy a (1932) oo lou 4J / derived that forsynthesi so f 1.0gra myeas t 1.467 gramo fglucos ei s required ifal lsubstrat ecarbo ni sincorporate d inth eorganism .H e established experimentally that2. 2 gramo fglucos ewa s requiredpe rgra m yeast formed,an dconclude d that0.7 3 gramo f glucosewa sburne d tosuppl y energy for theprogres s inth econversion s and theactivatio n ofcompounds , forreplacemen to f "lostheat "an d for achievemento fcellula r organization. A theoreticalbasi swh y0.7 3 gramo fglucos epe rgra myeas twa s respired, andno ttwic e orhal f thisamount ,coul dno tb e given.A distinctio nwa s madebetwee nbiosyntheti can dmaintenanc eprocesses ,i nbot h ofwhic h substrate isconsume d (Tamiyaan dYamagutchi ,1933 ,se eals oTerroin e and Wurmser, 1922).Th eobserve dfixe drati o ofth enumbe r ofgrammulecule so f substrateconsume dan d themaximu mdr yweigh to fth emicrobe s synthesized fromo rwit hi t (Monod, 1942;Siege lan dClifton , 1950;Rippel-Baldes , 1952) causedDeMos se tal . (1951)t oexpres s theirresult s asdr yweigh t ofth e organicmatte rforme dpe rmol e ofth esubstrat eutilized .Thi s "molar growthyield "i sfairl yconstan t fora largenumbe ro fbacteria lspecies , butdepend s considerably onth echemica lnatur eo fth esubstrate . Bauchopan dElsde n (1960)expresse d theyiel do f agrowt hproces sa s dryweigh t synthesizedpe rmol eAT P available fromth esubstrat ean dcalle d this theAT Pyiel d (Y )o fth egrowt hprocess .Thi swa sa n improvement ofth egra morganis mpe runi to fenerg y ratio,sinc eth eATP-yiel daccount s forth eavailabilit y ofth echemica lenerg yi nth esubstrat e toth eorganism . Theydemonstrate d that thisrati oi sremarkabl y constant fora larg enumbe r ofbacteria lspecie s andsubstrate s underanaerobi cconditions ,an di s approximately 10.5g organis mpe rmol e ofATP .Th esubstrate s theyus e consisted ofa mixtur e ofamin oacid s and otheressential s forcel lsynthesi s andsom ecarbohydrate ,whic hprovide d theenerg y foral lprocesse sbu twa s notassimilated .Onl y theAT Pderive d fromcarbohydrat ewa scounte d inth e calculationo fY .I nlate rexperiment sbot hlowe r andhighe rvalue so f Y havebee nobserve d inaerobi c and anaerobicmedi a (Stouthamer,1969 ; DeVrie se tal. ,1970 ;Stouthame r andBettenhaussen ,1973) .Calculatin gY underaerobi ccondition s theamoun to fAT P formedpe rmol eo fsubstrat emus t beknown .Th eP/ 0ratio ,however ,whic h iso fmajo rimportance ,ma y deviate considerably fromit smaximu mvalu eo f 3i nthes emicro-organism s (Stouthamer, 1969).Growt hyield sexpresse d ing organis mpe rJoul eo rpe r - 5 -
gram-electron available from the substrata are less constant than Y^ atp (Payne, 1970),whic h suggests that thefractio no fchemica lenerg y ina substratemolecul e thatca nb e transferred toAT P ismor emeaningfu l for biosyntheticprocesse s thanit stota lchemica lenergy . Inhi sboo k "PlantRespiration" ,Jame s (1953)describe d correlations ofplan trespiratio nwit hactivitie s and growthprocesses ,bu t couldno t decidewhethe r respiration isessentiall y anunavoidabl e anduseles s loss, orwhethe ri tresult s fromusefu lprocesses .Abou t synthesis ofalkaloid s andpolyphenol sh eremarked :"i tseem s littlebette r thana neve nchanc e thata metaboli creactio noccurrin gi na plan t tissuewil lb eo f anyrea l importance toit" .I na revie wGoddar d andMeeus e (1950)stat etha ti n rapidly growing cellsonl ya smal lfractio no f theenerg y released in respiration isrelate d togrowth .Beever s (1961), likeNeedha m (1964)an d Kleiber (1961)fo ranimals ,treate dcorrelation s ofplan tprocesse san d activitieswit h respirationan dgav ea detaile d accounto fth eglycolysi s and theKreb s cycle.Als oThornle y (1970),McCre e (1970)an dThornle yan d Hesketh (1972)hav e correlated growth andmaintenanc eprocesse swit h respirationb ymathematica l analysiso fexperimenta ldata . Animalhusbandr yha s supplied information about theretur no ffoo d withvaryin g chemicalcompositio n inhighe r animals interm so f increase in liveweigh tpe rweigh to f thesubstrate .Th emaxima lyield s reported exceed 0.5 ganima l (liveweight )pe rg food ,an d approachsometime s 0.7,dependin g onth egrowt h ratean d upon the typeo f foodan dproduc t (Brody, 1945; Blaxter,1962 ;Needham , 1964).Th e complexity of theprocesse s accompanying biosynthesis,suc ha sdigestion ,transpor tan dmovements ,maintenance ,an d thepractica lproble mo fmeasurin g thedr ymatte raccumulatio ni nlarg e animalsha smad ei tver ydifficul t forthi sdisciplin e toris eessentiall y abovea nempirica l level,excep t incase so f lactatean d fatproductio n (Baldwin, 1968;Va nEs , 1971). Amor e fundamental approachwa suse db yGunsalu san d Shuster (1961). They demonstratedho w theAT P requirementsma yb ecalculate d forbacteri a growingfro ma substrat e containingal l"buildin gblocks" ,th emonomers , usedi ncel lsynthesis .Forres tan dWalke r (1971)calculate d theamoun to f ATPneede d forsynthesi so f themonomer s from glucose and theirpolymerization , butneglecte denerg y required foractiv euptak eo f substratemolecules .Bot h setso fcalculation spredicte dmaximu mY valueso f about 30,whic hi s approachedb y thehighes tvalue s reported inliteratur e (about 24,b y DeVrie se t al., 1970).Pennin g deVrie s (1972, 1974a)calculate d thedr y - 6
matteryiel d ofgrowt hi nmaize ,bea n andsunflowe rplant s fromth e substrates glucosean dphotosynthate ,probabl yaccountin gfo ral lth e importantprocesses .A goodcorrespondenc ebetwee n thetheoreticall y established relativeyiel d andexperimenta ldat awa s shown,indicatin g that themetabolis m inhighe rplant sma yoperat ea tnearl y themaximu m efficiency allowedb y thebiochemica lscheme .
3.SOM EGENERA LCONSIDERATION SABOU TBIOSYNTHESI S
Or.basi so f theassumptio n thatal lsubstrat ecarbo nwil lb e found in theen dproduc t areactio nbalanc e fora conversio nca nb ewritte nwit h a knowledge ofonl y themolecula rcomposition s of substratean dend-product . Thisprocedur eha sbee n followedb y Tamiya (1932), Chen (1964)an dMorowit z (196S). Theassumption ,however ,i sno tcorrect :no t allsubstrat e carbon isconverte d intobiomas s carbon,an dno tal lbiomas scarbo ncome s fromth e substrate,sinc esom ecarbo ni sspli tof fa scarbo ndioxid emolecule s during carbonskeleto nreformation ,an dcarboxylatio n reactions mayoccur .I tals o gives incorrectanswer sbecaus e itdoe sno tconside r theenerg y required forconversion ,polymerizatio n andothe r activeprocesse s inherentt o biosynthesis,an d thusneglect s thesubstrat e required for theproductio n ofenerg y andit scombustio nproducts .Dependin gupo nth e typeo fsubstrate , product,an d conversionreaction ,thes e twoaspect sma yb eresponsibl e for considerable deviations fromth ebalanc e calculatedusin g themolecula r formula (Greencell s growingwhil ephotosynthesizin g area nexception . Netcarbo nuptak e anddr ymatte rproductio nar e thenrelated ,an d theexac t ratiobetwee n "substrate",consumptio n andbiomas s increase canb e calculated from thebiomas s "molecular formula".Th esituation ,however ,i nwhic h the substrateprovide s carbonan denerg y isth eusua lone ,an dwil lb e considered inthi s paper).
Theprocedur e followed incalculatin ga conversio n reactionbalanc e issummarize dbelo wan d schematized infigur e 1.Th e summation ofstep s ofreactio n chainsyield s anoveral lbalanc e forth e synthesis of amonomer , sucha sa namin oacid .Addin g thebalance so f anumbe ro f aminoacid san d accounting forpolymerizatio n cost gives thebalanc e fora protein . Balances forcarbohydrate s and othersubstance s canb emad e similarly. Ultimately,th esubstrat e demand forth esynthesi so f aggregates ofcompounds , likelivin gorganisms ,ca nb e established. Glucose isth edirec t substrate for synthesiso fman ymonomers ,bu t duringformatio no fnitrogenou s compoundsan d fattyacid s acetyl co-enzymeA , Figure 1.A schemati cpresentatio n ofsynthesi so f acomple xproduc tfro m glucose,includin g simultaneousnon-syntheti cprocesses .Oxyge n isth eonl y co-substrate andcarbo ndioxid e andwate r theonl y by-products,v ,w ,x ,y and zrepresen t thenumbe ro fmole s involvedan da ,b ,c an dd th etypes .
v glucose+ a + b •> xproduc t+ y .CO -+ z H„0+ c+ d (1)
c -> b +y 2 C02 (2)
d+ W j0 2- > y3 C02 +z 2H 20 (3) v glucose+ z ,H 20- * a (4)+
(Vj+ v 2)glucos e+ Wj O •>x produc t+ (yj+ y 2+ y 3> C02
+( Zj +z 2- z 3)H 20 (5)
+ w ner + CO + z H v„glucos e 2 °9 "*"e gy YA 2 4 2° ^+
(Vj+ v 9 +v 3)glucos e+ (Wj+ w 2)02 ->x produc t+ (yj+ y +y + YA)C02
+ (Zj+ z 2- z 3+ z^)H 20
(7) 7-
pyruvicacid ,oxalo-acetate ,aspartat ean d glutatnate(represente db y a andb infig . 1,eq . 1)ma yals ob eused .By-product s ofsynthesi si na n aerobicenvironmen t arecarbo ndioxid e andwater ,whil eothe r compounds may alsoremai n (eq. 1,c an dd ) .I nsom emicro-organism s and inanaerobi c conditions reactionby-product s consist ofpartl y oxidizedmolecules ,lik e acetate,ethanol ,lactat eetc .Unde r aerobicconditions ,no t fully oxidized by-productso f singlereaction sma yb euse di nothe rreaction s (eq.2 ,c ) and thoseno tuse dar eoxidize d (eq.3 ,d) .Synthesi s of theintermediate s which areno ta by-produc t ofothe rreaction s (eq.4 ,a )complete s the sequence.Summatio n ofth eequation s (1)- (4)yield s the reactionbalanc e forsynthesi so f therequire dend-produc t fromglucos ewit hoxyge nan d completely oxidizedby-product s (eq.5) .Equatio n (6)represent s the productiono fenerg y consumed innon-syntheti cprocesse srelate d togrowth , sotha tequatio n (7)give s thetota lo fsubstrat erequire d forbiosynthesi s of thisend-product .Th e finalequatio n represents themos tefficien t conversionpossible ,give n thebiochemica lmachinery .Wit h thisequation , conversionprocesse s caneasil yb eexpresse d interm so f grams ofglucose , oxygen,end-product ,carbo ndioxid e andwater . Anactua lconversio nbalanc e generally includesAT P andNADH„ ;thes e arerecyclin gintermediate s and areno toxidize d tocarbo ndioxid ean d water.ATP ,CTP ,GTP ,TT Pan dUT P are takent ob e similarwit hrespec t to theirabilit y totransfe renergy .I ti ssuppose d thata nAT P •*•AM P conversion canb ereplace db y 2AT P•* •AD P reactions.Th edehydrogenas e co-enzymesNAD , NADP andFA D alltransfe rprotons ,bu toxidatio n ofFADH _ inth e "respiratory chain"yield sonl y 2AT Pmolecules .Wherea sNADH -yield s 3;NADPE L isno t oxidized inthi smulti-enzyme-complex . Thehydroge no fNAD H canb e transferred toNAD P onlywit h energy supplied fromATP ,bu t therevers e doesno tyiel dATP .Fo r simplificationo f thecalculation s and presentation only thereaction sAT P-* •AD P andNADH „-* •NA Dwil lb e used inthi spaper .I f necessary,calculation swil lb e adjusted forthi sdifference .I n thepentos e phosphatepathwa yNADPH „ resultsdirectl y fromsubstrat edegradation ,bu t thispathwa y isno t intensively used inplant s (Beevers, 1961). Iti s assumed thatal lth eenerg y andhydroge nproductio n occursvi a theKreb s cyclean dnon e inth epentos ephosphat epathway .Becaus eo f thesmal l differencebetwee n thesetw opathway s inthes erespects ,th eerro r resultingfro mthi ssimplificatio n isnearl y alwaysnegligible .
Whenth eoveral l reactionbalanc eo fa biosyntheti cproces si s simplified toit sfina lversio ni nwhic h only glucose andoxyge nar e - 8
substrate (withnitroge nan dsulphu ri fnecessary )an d therequire dproducts , carbondioxid ean dwate rar eforme d (fig. 1,eq . 7), variables characterizing the conversionca nb e calculated,bein gth e"productio nvalue "(pv) ,th e "oxygenrequiremen t factor"(orf )an dth e"carbo ndioxid eproductio n factor" (cpf).Thes ear edefine di ntabl e 1.Wate ran dhea twil lno tb e considered separatelybecaus emostl y theirformatio ni sdifficul t tomeasure .P v (table 1)resemble sPfeffers '"Oekonomische nKoeffizient " (seeTamiya , 1932),whichrepresent s thenumbe ro fgram so forganis m formedpe r 100g o f substrateused ,bu tp vdiffer s fromth elatte r asp v characterizesbio - synthesis and theprocesse s inherent toit ,whil e theO.K .account s for structuremaintenanc eprocesse sa swell .Pv ,or fan dcp f arecharacteristic s strictly for grossdr ymatte rformation . Theenerg y conversionequatio n
1Joul eglucos e-* •0.7 9 Jouleplan tbiomas s+0.2 1 Joulehea t (Eq. 1) caneasil yb e derived fromequatio n 1,whic hrepresent s thesam ebiosyntheti c process expressed ingrams .A similarcomputatio na sth eon emad et o obtainequatio n 1can ,i nprinciple ,b emad e toobtai nequatio n 2usin g thespecifi cheat so fcombustio no fcompounds .However ,thi s ismuc hmor e difficult,i fa tal lpossible .Bot hset so fcalculation s startwit hth e molecularreactio nequation s forsimpl e conversions (fig. 1,eq .1-4) . Theseequation s caneasie ran dmor e accurateb e "translated"int oa weigh t balancetha n intoa nenerg ybalance .Th eamount so foxyge nan dcarbo n dioxide involvedcanno tb eexpresse d inJoules ,s otha t theenerg y equation doesno tprovid einformatio n onth ega sexchang eo f theconversions .Th e fractiono f theenerg y fromAT Pmolecule s retained inreaction si s difficult toestablish ,an d itdepends ,amon gothers ,o n the concentration of compounds inth ecell .Bu t thenumbe ro fmole sAT Puse d inbiosynthesi s canb e counted easily,becaus eman y reactions operatewit h theenerg y supplyo fexactl y oneAT Pmolecule ,independen to f theefficienc y ofit s utilization.Th eremainde ro fAT Penerg y is losta sheat .I nphosphorylation , forinstance ,on eAT Pmolecul e isalway sinvolve d andno t anamoun to f energy thatca nb e calculated fromth echang e infre eenerg y of formation of thereactant s dividedb y theaverag eenerg y efficiency ofprocesses .I t couldb eargue d thatinstea d ofon eAT Pmolecul epe rreactio n twoo rmor e couldb e involved,fo r instance,i ncas eo f ahig h end-product concentration. This isunlikely ,becaus eth eenerg y supplied byAT P is generally inexces s ofth eneed s (Krebsan dRomberg , 1957;Lehninger , 1965). Iti s therefore concluded that the "energyefficiency "o fbiosynthesi s of anorganis m from Table 1.Th e variables characterizingbiosyntheti cprocesses .
Units:g. g and gjnole.g .
' Name Symbol Definition
production value pv weighto fth een dproduc t weight ofsubstrat erequire d for G-skeletonsan d energy production
oxygen,requiremen t orf weight of oxygen consumed factor weight ofsubstrat e required for C-skeiatons andenerg y production
carbondioxid e. cpf weight ofcarbo n dioxide produced productionfacto r weighto fsubstrat e required for C-skeletonsan denerg y production
hydrogen hrf gmoleso f NADH required requirement factor weight ofen dproduc t
energy requirement erf gmoleso fAT P required factor weight ofen dproduc t - 9-
a substrateca nb edetermine dexperimentally ,lik eth e "weightefficiency " bymeasurin gheat so f combustioninstea d ofweights .Bot hvalue s canb e usefulan dconverte d intoon eanother .Bu tth e"weigh tefficiency "i sals o predictable frommor ebasi cdata ,whil e inpractic e the "energy efficiency" isnot .
3.1.THE_REACTI0N_BA^CE_FOR^SYNTffiSIS_gF^MgNOMER S
Thereactio nequation s used inth ecalculation s described inthi s paperwer e constructed frompathwa y dataa spresente d inth eexcellen t bookb yDagle y andNicholso n (1970), showingman y stepso fnearl yal l relevantconversion s indetail .Th epathway s forsynthesi so flignin , deoxyribose,fructosa nan dchiti ncoul dno tb e foundan d therefore estimated. Thecharacterizatio no f compounds likehemicellulos eha sbee ngreatl y simplified.Tabl e2 present s thereactio nbalance suse di ncalculatin g the values characterizing aconversio nproces s fromglucos e intoorgani cdr y matteri na standar d format;AD P andNA D areno tquoted .Al lreaction sar e inth eform :
1glucos e+ 1AT P -*•1 fructos e (Eq.2 ) (reactionnumbe r 205)
and
1pyruvi c acid+ 1asparti c acid+ 1NH ~- 1C0 2 -3 H 20+ 3 NADH 2 '+3 AT P-* -1 lysin e (Eq.3 ) (reactionnumbe r 127)
Note thatwheneve rNADPE L isrequired ,fo rinstanc e for fattyaci d synthesis,thi si spresente d asNADH 2 plus 1AT Ppe rNADH 2molecule . Alternative syntheticpathway s are listed ina norde r of decreasing probability inhighe rplants ,i ns ofa ra sindication s couldb e found. Thefigure si nth e tablerepresen t thenumbe ro fmolecule s involved in thesynthesi so f 1molecul e of theproduct .Glucose ,pyruvi cacid , acetylcoenzy mA ,serine ,asparti caci dan dglutami c acid are takent o be the (co)-substrates.A s therear e"families "o fderivate s fromon e commonintermediate ,th eprocedur e followeddurin gcomputatio nwa s first todetermin e therequire d."..mount so fintermediate s and,i na secon d phase,t ocalculat e theamoun to fglucos erequire d for synthesiso f thesecompounds . Table2 .Basi cdat afo rconversio n reactions,a sderive d fromDagle yan d Nicholson (1970).Eac hbalanc egive s thenumbe ro fmole s involved insynthesi s ofon emol eend-produc t (prod),th enam eo fwhic h isgive ni nth e lastcolumn .Substrat e forconversio nma yb e glucose (glue),pyruvi caci d (pyr),acety lcoenzym~ A (AcoA), serine (ser),asparti caci d (aspa)o rglutami caci d (glua).
Furthermore,th eNEU ,H.S ,CCL ,0- ,H^O ,NADH 2 andAT P involved inth ereaction sar eindicated .Th e firstcolum ngive sth e numbero fth ereaction .M Wrepresent s themolecula rweigh to f theend-product .Meanin g ofnote s (column16) : 1.1 production ofon eTHF- Cgrou p during conversion
-2.1 consumptiono fon eTHF-CH 2grou p duringconversio n -3.1 " " oneTHF-C O " " " -3.2 " " twoTHF-C Ogroup s " " -3.3 " " threeTHF-C Ogroup sdurin g conversion 10 doesno toccu ri nplant s 11 authorsestimat e 12 Embden-Meyerhof-Parnaspathwa yo rEtner-Douderof f pathway 13 cellulose,glycogen ,starc han damylopectin e 14 polymero fmannos ean dxylos e 15 polychitobiose 16 polyconiferylalcohol,pathwa y estimated TABLE % COUrUUc.D
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Single-carbon-groups are transferredb y tetra-hydro-folicaci d (THF). Thesegroup sar eindicate d incolum n 16o ftabl e2 an dexplaine d inth e tablecaption .Thei rproductio nma y occuraccordin g to
1glucos e+ 2 TH F+2THF- C + 1pyruvi caci d+ 1C0 2 + 1H 20+ 3 NADH 2 (Eq.4 )
andal loveral lexces si sessentiall y removedb y thereactio n
1THF- C +2 H 20-* • C02 +2 NADH 2+ TH F (Eq.5 ) (Dagley andNicholson , 1970)
Itshoul db enote d thatth emajorit y ofpathway shav ebee nestablishe d in micro-organisms andi nspecialize d animaltissues .However ,i tma yb e assumed (Dagley andNicholson , 1970)tha tothe rorganism sd ono thav e metabolicpathway s deviatingmuc h fromth eknow nones .
3.2. IN0RGMIC_M0LECULES
Biomassofte ncontain s inorganicatom san dmolecules ,som eo fwhic h areincorporate d inorgani cmolecules .Th eincorporatio nreaction s occur spontaneously .Nitrat ean d sulphate aretake nu pan dsubsequentl y reduced. According toBandursk i (1965)nitrat ei.Juctio nca ub e summarized by the equation
N0~+ 4 NADPH 2-» •NH 3 +2 H 20+ 0H ~+ 4 NAD P (Eq.6 )
Reductiono fon esulphat emolecul e requires 4AT Pmolecule smore .Reductio n ofon emol eo fnitrat eo rsulphat e consumes thehydroge nan d energy obtained fromabou t0.3 5mol eo fglucos e andappear s tob e anexpensiv eprocess . Feedingyeas twit h carbohydrate andnitrat eyield s 0.35 gramyeas tpe r gram carbohydrate,an dmor e (0.45 gram), ifammoni a isth esourc e ofnitroge n (Terroinean dWurmser , 1922).Wesseliu s (1973)observe d ayiel ddecreas eo f 30% i fphotosynthesizin g algaewer e fedwit hnitrat e instead ofammonia . A similar trendca nb e seeni nfig .2 ,3 an d4 .I nhighe rplant s reduction ofnitrat ean d subsequent incorporationo fnitroge nint oamin oacid s occur duringphotosynthesi s inleave sunde rcondition so f adequatenitroge nsuppl y (Beeversan dHageman , 1969;Bornkam , 1970).Thu s theassimilat e consistso f sucrosean damin oacids ,an dcro pplant s suppliedwit hnitrat ed ono tsho w a dropi nyiel dpe rgra mo fassimilate s ascompare d toammoni a fedplants . Thesean d otheraspect so fth erelation sbetwee nprocesse s occurring during photosynthesiswer eelaborate d andevaluate dexperimentall y elsewhere (Penningd eVries , 1974a). - 11 -
3.3. SrjtfTHESIS_0FJ|9L^RS_^^
3.3.1.Polymerizatio n
Mosto fth ecel lplasm aan dth ecel lwal lar epolymers .Polymerizatio n ofmonomer srequire s3 o r4 molecule so fAT Ppe r aminoaci d (oneAT P-* •AM P conversionand ,accordin g toLucas-Lenar dan dLipman n (1971)on eo rtw o GTP•+ •GD Pconversion s inribosoma laction) ,2 pe rnucleotid emonosphosphat e andals ofo rmos to fth e(no nphosphorylated )carbohydrat emonomers .Th e lowervalu efo ramin oaci dpolymerizatio nwa suse d forcalculatio ni n "standardconditions" . Theenerg yconten to fth ehydroge nbonds ,whic hwit h sulfidebond sar e responsible forth esecondar y andtertiar y structureo fpolymer san dpolyme r aggregates,i slo wcompare dwit h thebond swithi nan dbetwee nmonomers . Thesear eassume d toevolv espontaneously ,o rt orequir eonl y anegligibl e amounto fenergy .Formatio no fsulfid ebond syield sNADI^ .I ti sgenerall y assumed that thesecondar y and tertiarystructur eo fprotein s isdetermine d by theamin oaci d sequence,an d thekinetic so f foldingo fth eamin oaci d chaindurin g itsassembl yo nth eribosomes . Duringpolymerizatio nwate r isspli toff ,mostl y onemolecul epe r monomer.Accountin gfo rsuc hchange si nth eoveral lreactio nequatio n completes thecalculatio no fth edirec trequirement s forbiomas ssynthesis .
3.3.2.Tool_maintenanc e
Therat eenerg yexpenditur e formaintenanc eo f thetool s forbio synthesis,RN Aan denzymes ,i s treated independently and separately from othermaintenanc eprocesses ;th elatte rwil lb e called"structur e maintenance".Th erat eo f "toolmaintenance "depend s onth eamoun to ftool s ando nthei rstability .I fbot h areunaffecte db y therat eo fbiosynthesis , toolmaintenanc e isconstan tan dca nb e determined togetherwit h structure maintenanceprocesses .However ,i f theamoun to fmRN A (themos tunstabl e fractiono fRNA )control s therat eo fprotei nsynthesi s (assuggeste db y Goodwin,1963 ;Lavall ean dD eHamer , 1970,an d others),an d ifenzym e activityi sregulate daccordin g tocel lneeds ,i ti slikel y that these quantities arerelate d toth erat eo fbiosynthesis .N o indicationo fa relationshipbetwee nth estabilit y ofenzyme san dRN Aan d growthrat ei n eukaryoteswa s found,althoug h therema yb e sucha relationshi p forRN A inbacteri a (Salsere tal. , 1968;Norri san dKoch , 1972).Fro mSalse re t al. (1968)an dGeidusche k andHaselkor n(1969 )i tca nb ederived , thatmRN A - 12
moleculesi nbacteri aar euse dabou t2 0time sbefor e theyat odegraded , andi ti sassume dtha tthi s isa fairl yconstan tvalue .Fo r thisassumptio n islittl eevidenc e (Bielka, 1969),bu t counter-evidencewa sno tfound .Srne» . (re)synthesiso fa codo nfro mmonomer srequire s6 AT Pmolecules ,0. 3AT P moleculepe rpeptid ebon di sneede dfo rmRN Amaintenance .Othe rRN Afraction s areknow n tob emuc hmor e stable (Geiduschek andHaselkorn , 1969), sotha t theirturnove rdoe sr.o tdoubl e theRN Amaintenanc ecos t perpeptid ebond , inspit eo fthei rlarge ramounts .Ther ei sn oindicatio n thathighe rcos t is incurredi nhighe rorganisms . Amountan dhalf-lif eo rmos tenzyme sinvolve di nbiosynthesi san d relatedactivitie s areunknown ,excep ti nsom especialize dmammalia n tissues.Synthesi s ofribosoma lprotein sma yb erelate dclosel y toRN A synthesis (Schweet andHeinz, 1966).Fro mdat ao fStrehle r (1963)an d Schimkean dDoyl e (1970)i ti sestimate d thati nslowl ygrowin g -issues 5 to5 0% o fprotei n synthesisi sresynthesi so fhydrolize dproteins .O n thebasi so f thisinformatio ni twa sassumed ,somewha tarbitrarely ,tha t theprocesse so ftoo lmaintenanc e canb eaccounte d forb yincreasin gth e cost ofpolymerizatio n ofamin oacid san dnucleotide sb y 1AT Pmolecul e permonomer .Quantitatively ,th eturnove ro fothe rcel lsubstance s ismuc h lessimportant ,a swa s shownfo rinstanc ei nexperiment so fBielesk i (1972) forphospholipids .Du et oth emor e complexnatur eo fsynthesi so fnitrogenou s compoundstha ntha to fothers ,i tma yb eexpecte dtha t toolmaintenanc e ismor eimportan t forsynthesi so fth eforme rcompound s thant o synthesis ofnitroge n freecompounds .Fo rpurpose so fcalculation ,i ti sassume d that therat eo ftoo lmaintenanc e isproportiona lt oth erat eo f synthesis ofamin oacid san dnuclei cacids .Thus ,thi sproces s isaccounte dfo ra s parto fth ebiosynthesi so fnitrogenou scompounds .
Maintenanceo fenzyme san dRN Awa sestimate d onth ebasi s ofexperiment s torequir e about5 mol eAT Ppe rmol emonome r formil kprotei nproductio n incow san dabou t 20durin ganima lgrowt h (VanEs ,1971) .Estimate s onth e basiso ftheoretica lspeculation s are2 AT Ppe rmonome r forprotei n synthesis inhighe ranimal s (Baldwin,1968 )an d3 i nmicrobe s (Woldendorp, 1971). Forrestan dWalke r (1971)use dBaldwin' sestimate . Theeffec to fvariou svalue so ftoo lmaintenanc eo nth eyiel do f conversiono f 1g glucos e into"nitrogenou scompounds "(fo rit schemica l composition,se etabl e3 )an d theamount so foxyge nan d carbondioxid e involvedi nthi sproces s are giveni nfig .2a .Fig .2 bi sa simila r figure forsynthesi so fmaiz eplan tbiomass .Thes e figurespresen tresult so f / i \ \ A CD \ fM I J \ A' 01 \ a Ul j j \ o a: \ < I j \ o O 1 I \ \ z u. \ \ \\ ">£ «- < \ \ '« UJ _l 1 / \ - o •** \ a. t- ml Iml x\ o»\ X _ < CO x/ O / z z *, z CJ z/ Z / °\ U. \ li. >\ U- — CU l-< it \ O 3 > / > / z ' o -a o a./ a. J o \ o .\o "0 c cu ° \ cd a \ «» to a cfl o \ cu 4J Q a \ \ V\ CO C - CN c \ •H •H a H \ \ w (3 •H a CO o CO \ " a) to 1 4J o \ 4-1 •H j o T3 1 I 1 . > 1 \ . 1 M U £3 I i O a> to CM P. cu © o" o' d 1-4 ft. u. a O a. o u-4 PL, U o CO H CU . Q CO o o o •iH c 4-1 CO t-4 o CO 3 o •H O a 4J M •H CO CU a N 4-> •H •r-l CJ > Cd M cu a cd CO CO >^ J3 CO r-t O CO cu O •H u P. C CO O
ofcalculations ,fo rwl.ic hther ei sa sye tn omean so f experimental validation.I ti sno t suggested that therat eo f toolmaintenanc evaries, but theeffec twhic hdifferen tvalue swoul dhav e isshown .
3.3.3.Biomas ssynthesi sfrom_polymer s
Considering finally thesynthesi so flivin gbiomas s thequestio n arises whetherchemica lenerg y isrequire d toconstruc t frompolymer sth emacro - molecular aggregates thattogethe rmak eu pth elivin gbiomass .I ti s generally,an d tacitly,assume d thatbiomas sevolve s spontaneouslywhe n itsprecursors ,th emacromolecules ,ar epresen t (e.3 .Lehninger ,1965 ; Forrestan dWalker , 1971).N odat ahav ebee n found inliteratur eo nth e heat ofcombustio no fbiomass ,bein gdifferen t fromth esu mo f theheat s ofcombustio n itscontributin gpolymer s separately.Meyerhof f (1024)foun d that theheat so fcombustio no flivin gan dquickl ykille derythrocyte s are exactlyequal .Althoug h dead,cel lorganelle swil lstil lhav ebee npresen t and thisexperimen t thereforedoe sno t giveexactl y theevidenc e required. Krebsan dRomber g (1957)remar k thatenzymati cbreakdow no fbiomas sint o monomersdoe sno tyiel dAT P andsugges timplicitl y thatmost ,i fno tall , energyrelease d inbreakdow n tomonomer smus tb eascribe d topolyme r hydrolysis.Breakdow no fmacr omolecula r structureso rpolymer s intomonomer s doesno trequir e chemicalenerg y todisrup tbond sbetwee npolymer so r monomers,som ereaction s requirea catalyst .Th econclusio nma y therefore be drawntha tth efre eenerg y offormatio no fbiomas s isno tnoticabl y different fromth esu mo f thefre eenergie so f itspolymer s separately,an d thathardl y anychemica lenerg y isstore d inth especifi cmacromolecula r structures. Theoreticalevidenc e for thisstatemen t ispresente db yMorowit z (1968, pg.98 )wh o calculated that thechang ei nhea to fformatio nfo r polymerizationplu ssynthesi so fbiomas s frompolymer sequal s 16ca lpe r grambiomas s andth echang e infre eenerg y of formation7 8ca lpe rgra m biomass,th edifferenc ebein g thehea t givenu pi nthes eprocesses .Thi s heat,divide db y theabsolut e temperature atwhic h thereactio noccurs , represents theentrop y increaseo fbiomas s andenvironment .Mos to f this changei sbrough tabou ti npolymerization .Thes evalue s aresmal lcompare d toth etota lfre eenerg y andhea to f formationo fth ebiomas s (5500an d 5400ca lpe r gramrespectively) .Th eefficienc y of transfero f chemical energy fromon emolecul e toanothe r isususal yhig h (over5 0% )an d although theenerg yefficienc y ofth epolymerizatio nproces s is alreadymuc h less - 14-
(about2 0 %), iti sas sime dtha tn omor etha na negligibl eamoun t ofAT P isspen ti nth elas tste po fbiomas ssynthesis ,i fany .Thi s conclusion is extrapolated toformatio no fmulticellula rorganism s fromcells .Gorsk i (1966)ascribe s toth especifi carrangemen t ofatom si na myceliu ma decrease inentrop ywit hrespec t toth eunorganize d stateo f thesemolecules , which issmal lcompare dwit h thetota lentrop yproductio ndurin g aerobic growtho na glucosesubstrate . Itma ysee mremarkabl e thatorganize dbiomass ,containin gmuc hmor e biologically relevantinformatio n thana simila ramoun to funorganize d polymers,ha sabou tth esam efre eenerg yan dhea to fformatio n asth esam e polymers ina nunorganize d state.I tshould ,however ,b erealize d that the thermodynamicalconcep t "order"refer st oarrangement s ofatom san d molecules ina system ,an di sdifferen t fromth e "meaning" (or "information") which thecel lan d thebiologis tattribute s toth esam eentit y (Makkink, 1971).Thi si seasil y seenb y comparing theinvarian tentrop y ofequa l amountso fDN A oftw odifferen tbacteri aspecie swit h itsinformatio n for thebiochemica lmachinery ,whic hproduce s twodifferen torganisms .
3.4. NQN_SYNTHETIC_ACTIVITIES_DURI^_BIOSYNT
Thebul k flowo fwate r through theplan t isa passiv eprocess .Cel l elongation andth ebuild-u po rmaintenanc eo fa turgo rpressur e isno t accomplishedb yactiv ewate rtransport ,bu ti nrespons e toactiv e ion uptake,s otha tplan t growth inthi sstud yca nb elimite d todr ymatte r accumulation.Mechanism s foractiv etranspor to fion s acrosscel lmembrane s areno tye tunderstoo d (Kaback, 1970).Dat acollecte db y Beevers (1961), Stein(1967 )an dSchoffeniel s (1967)demonstrat etha t thepassag eo fth e outercel lmembran eb yon ecatio nrequire s theenerg y of approximately 0.3AT Pmolecule ,whil eth eanio nfollow spassively .O nth ebasi s ofth e Mitchellchemi-osmoti chypothesi s itma yb e expected (Lehninger,1971 ) thatpe rpai ro fproton s transferred fromNADH _ tooxyge nsi xpositiv e chargesca nb eimporte d intomitochondria .Experiment sb yMitchel lan d Moyle (1968)wit hra t livermitochondri a support thishypothesis .I ti s likely,however ,tha ti nplasmalemm aan dtonoplas t adifferen tmechani m forio nuptak e isactive ,sinc eproto ntransfe r tooxyge noccur s only in mitochondria.Th eexperimenta lvalu eo f0. 3mol eAT Ppe rmol eo f cations importedwil ltherefor eb euse drathe r thanth etheoretica lvalu eo f 0.5 moleAT Ppe rmol ecations .Translocatio n intoth evacuol e is assumed to requirea nequa lamoun to fenergy . - 15-
Inorganicmolecule sar etreate da son egroup ,nitrat e and sulphate excluded,o fwhic hth eaverag emolecula rweigh t is75 .A mor e detailed consideration isno tusefu lbecaus eo f thesmal lamoun t ofenerg y involved intranslocatio n and lacko finformatio nabou tth eunderlyin gprocesses . Most of thevolum eo fmatur eplan t cells isi nth evacuol e andmos to f theion sar epresen t inthi scel lorganelle .I t isassume d that7 0% o fth e inorganicmolecule s islocate d inth evacuol e and 10% i nth eplasma .A n arbitrary figureo f2 0% i stake nt orepresen t theinorgani ccel lwal l incrustrations.However ,th eeffec to f thisassumptio no nth eresul to f thecomputation s isver ysmall . Mosto fth eimpor to forgani cmolecule s intocell s isactiv e(Kaback , 1970;Hofer , 1971;Payn ean dGilvarg , 1971).Th emechanism s ofthes e processes arestil luncertain .I ti sestimate d fromdat ao fBeever s (1961) andAlber s (1967)tha t theuptak eo fon ecarbohydrat emolecul e requires the energyo f 1molecul e ofATP .Thi si si nagreemen twit huptak e of carbohydrates through temporaryphosphorylatio n ofth emolecule ,a ssuggeste db yKabac k (1970)an dOxende r (1972). Phagocytosis andpinocytosi s aren^ tlikel y tob ea cheape r alternative forsingl emolecul euptake ,a s themembran eenvelopin g themateria l transportedha st ob e "digested"an dreplaced .Bu tsometime s iti sth eonl y way fora cel l toobtai nit ssubstrate ,a sfo rexampl e forParameci a consumingbacteria .I nhighe rplant s thisuptak emechanis mi sprobabl y notutilize dbecaus e substratemolecule s arealway so flo wmolecula rweight . Here,substrate sar eofte ntransporte d overman y centimeters.Energ ycos t forthi sproces swil lno tb econsidered . Heati sver yseldo ma mai nproduc to fsubstrat edegradation .
4.VARIABLE S CHARACTERIZINGBIOSYNTHETI S
Growthresult s fromsynthesi so fmixture s ofcompounds .Th eamoun to f glucosean d intermediates required forbiosynthesi s ofplan tdr ymatte r mayb ecalculate d fromit schemica lcomposition ,a nexampl e ofwhic hi s giveni ntabl e3 ,usin gdat ao f table2 .Tabl e4 represent s theassumption s andcondition suse d forstandardize d calculations.Aromatic ,secondar y plantsubstances ,hormone s etc.are ,dependin go nthei rchemica lpropertie s andanalytica lmetho dused ,foun di non eo f themajo r fractions.Thi s simplification causesonl y smallerror s duet oth e lowquantitie s involved. The typean damoun to fexcrete d compoundsshoul dals ob e considered if micro-organisms arestudied . Table 3- The chemical composition of a young and vegetative roaise plant. All fractions are expressed on a dry weight basis.
II.. .1 .•.HI Ml- HI .L 1 • T mainfractio n subtractions note
uitrogeuous compounds 23 % amuseacid s 10% amino acidcomposition ,o fze i proteins 87% (Handbook ofBiologica lData , nucleic acids 3% 1956) :
carbohydrates 56,5 ribose t% glucose5 % fructose2 % marinese 1% galactose 1% sucrose 5% cellulose 40% hemicellulose4- 0% pectin 5%
glycerol- lipids 2,5 % composi tioi io fmaiz eoi l tripalroitate 12% r (Wintonan dWinton , 195Q) ! glycerol- i tristearat e 3% glycerol- trioleate 47% glycerol- trilinolate 33% glycerol- trilinoleate 5%
lignin(nitrogen-free ) 8 % poly-coniferylalcohol, percentagebase d onMulle r et.al. (1970)
organicacid s 5 % oxalic acid 5 Z 1 glyoxalicaci d 5% j i f oxaloacetic acid2 0% malic acid 10 % citricaci d 30% accniticaci d 30%
potassium8 0% rainerals 5 % chloride 20% | • • Table4 .Standar d conditions andassumption s usedi ncomputation s
- chemicalcompositio n ofbiomas sa sgive ni ntabl e3 i - allprocesse s occurunde rfull yaerobi cconditions . -polymerizatio no famin oacid srequire s 3AT Pequivalent spe r peptidebond . - enzymean dRN Amaintenanc e duringprotei nsynthesi srequire s1 moleculeAT Ppe rmonomer .Othe rmaintenanc eprocesse s (maintenance ofstructures )ar eno tconsidered . - transport across theoute rcel lmembran erequire s 1mol eAT Ppe r moleorgani cmolecule sand0. 3mol eAT Ppe rmol eo finorgani c molecules. - intra-cellulartranslocatio noccur s spontaneously,excep tpassag e of thevacuol ea^ dmitochondri amembranes ;transpor tacros s these membranes isactiv ean d requires 1mol eAT Ppe rmol eorgani c moleculesan d0. 3mol eAT Ppe rmol einorgani cmolecules . - spatialcompartmentatio no fonl y fatty acidsynthesi s (inmitochondri a instead ofhyaloplas m) an d ligninprecursor s (formed inhyaloplas m butincorporate d incel lwall) ;n o temporalcompartmentatio n of syntheticprocesses . - glycolysis,tricarboxyli c acid cyclean doxidativ ephosphorylatio n are usedfo rNADH -an dAT Pproduction . - P/0rati ofo rNADH „oxidatio ni s3 . - 16-
Thereactio nequatio nresultin gfro msummatio no fth e individual balancesfo ral lcompound sma y showa nAT Pan dNAD H excesso rshortage . Overproduction ofNADH- ,whic h isofte nfound ,i sme tb y itsoxidation , usually generatingATP .A calculate d excesso fNADE Umus tb e eliminated by itsoxidatio nwit hoxygen ,an dno tb e reducingothe rcompounds ,becaus e
theexperimentall y determined chemicalcompositio nmus tb e achieved.NADH 2 orAT P shortage iseliminate db yadditiona lsubstrat edegradation .Onl ya n excesso fAT Pca nb eeliminate dwithou t changing thereactio nequation : thecel lma yhydrolyz e theexcess ,o rpreven t theexces s formationb y uncouplingphosphorylation .Excessiv e formationo fAT Pma y occur,bu ti n most casesth eAT P formedi nsyntheti cprocesse s isconsume d completely in polymerization and translocationprocesses .Th evalue scharacterizin ga conversionproces s (pv,or fan dcpf )ca nb e appliedfruitfull y only to thetota lo fprocesses ,th etota lbein gdefine d asth esu mo f those processeswhic hd ono texchang eATP ,NADE L orintermediate swit h their environment.Fig .2 aan db showtha tbiosynthesi s ofprotei no rbiomas s fromglucos ewit hNE L causesa nexces so fenergy ,whic hevolve d duet o oxidationo fth eremainin gNADEL :a tth e (unrealistic)lo wvalue s ofenerg y consumptiondurin gpolymerizatio n theproductio nvalu eo f theproces sdoe s notdecreas ea tincreasin gcos t ofpolymerization . Theresul to fa syntheti cproces s inwhic hglucos ewit hNH ,an dH„ S isconverte d intoplan t drymatter ,wit h achemica lcompositio n asgive n intabl e3 ,ca nb edescribe d as
1.0 gglucos e+ 0.03 1 gNH 3 +0.00 1 gH 2S+ 0.10 3 g0 2+ 0.03 9g min .
•*•0.74 6g plan t+ 0.17 7 gC0 2 +0.25 0g H 20 (Eq.7 )
Withnitrat ean dsulphat e theequatio ni s
1.0g glucos e+ 0.10 1 gN0 ~+ 0.00 3g S0 4~+ 0.12 2 g0 2+ 0.03 4g min . -*-0.65 1 gplan t+ 0.34 3g C O +0.26 6g H„ 0 (Eq.8 )
Standard conditions,give ni n table4 ,ar euse di ncalculations ,unles s specified otherwise.Fro mthes ereactio nbalance s it follows thatp v for synthesiso fplan tmateria l fromglucos ean dNE U andEL Si s0.746 ,an d - 2- 0.651 ifnitroge n and sulphur are supplied asNO ,an d SO,• .Th evalue so f orfan dcp far e0.103 ,0.122 ,0.17 7 and0.34 3respectively .I nth econversio n equationsth esu mo fth eweight so f thesubstrate s is,o f course,equa l toth esu mo fth eweight so fproduc t andby-products . Infig .3 ar erepresente d thevariable s characterizingbiosynthesis , pv,or fan dcpf ,o fnitrogenou s compounds,carbohydrates ,lipids ,ligni n Figure 3. The variables characterizing biosynthesis of nitrogenous compounds with ammonia and with nitrate, of carbohydrates, of lipids, of lignine and of organic acids.
nitrogenous lipids compounds (with ammonia) pv = 0.616
T pv =• 0.330
cpf = 0.256 orf = 0.137 cpf = 0.530 orf - 0.116
t—- •<
nitrogenous lignin compounds pv = 0.404 (with nitrate) pv = 0.465
cpf = 0.673 orf - 0.174 cpf - 0.292 orf - 0.116 • t i ' •
organic acids carbohydrates
pv = 0.826 pv « 1.104
cpf - 0.102 orf • 0.082 cpf =-0.050 orf - 0.298 - 17-
andorgani cacid sa sforme d fromglucose .I ti sno tsurprisingl y that important differencesexis tbetwee nthes efractions .Th eslightl ynegativ e valueo fcp fdurin gformatio no forgani cacid si scause db ycarboxylatio n ofpyruvi cacid . Morowitz(1968 )calculate d thati f
1.00g glucos e+ 0.1 2g NH 3+ 0.0 2g H 2S04+ 0.0 5g H 3P04 wereconverte d into
0.77g bacteri adr ymatte r+ 0.2 4g H. O+ 0.0 9g C O (Eq.9 ) bothth echang ei nfre eenerg y offormatio nan dth echang ei nhea to f formationo fthi ssyste mwoul db enegative ,showin gtha tther ei shea tan d entropyproduction .Sinc eMorowitz' scalculation sneglec t theenerg y spent innon-syntheti cprocesses ,hi sequatio noverestimate s theconversio n efficiency.Th ebiosynthesi s equationcompute d according toth eprocedur e described abovefo rbacteri awit ha simila relementar y compositioni s
1.0g glucos e+ 0.10 9g NH „+ 0.00 8g H 2S+ 0.15 2g 0 2+ 0.05 6g min .
-»•0.67 8g biomas s+ 0.26 3g C0 2+ 0.38 2g H 20 (Eq.10 )
Equation (10)yield s lessbiomas s than (9),thu smor esubstrat ei soxidize d toproduc eenerg yan dmor ehea ti slost .I tca nb econclude d thatth e resulto fth ecomputatio npresente d isno ti nconflic twit h thelaw so f thermodynamics.Th edifferenc ebetwee nequation s (10)an d(7 )i smainl y causedb yth ehig hconten to fnitrogenou s compoundsi nthes ebacteri a (64 %). Thefigure s4 a- fdemonstrat e theeffec to fvariou s chemicalcomposition s ofsynthesize ddr ymatte ro nth evalue scharacterizin g theconversion .I n these triangularplot sal lcombination so fthre e components canb e indicated. Becauseth eorganis mconsist so fsi xmai nfractions ,a simplificatio ni s necessary toplo ti nthi s format.Th efraction so fnitrogenou s compounds, fatsan dcarbohydrate swil lb econsidered ; 10% o fth eweigh to fth e carbohydrate fractioni stake nt ob eligni nan dorgani cacid san dmineral s areeac hassume dt ob e5 % o fth etota lbiomas sweigh ti nal lcases .I n thiswa ythes e triangles roughlycove rman yo fth echemica l compositions foundi ntissues .Figure s4 a- csho wth econversio n characteristicswhe n ammoniaan dhydroge nsulfid ear esupplie dwit h glucose,an dfigure s4 d- f whennitrat ean dsulphat eer egiven .Th eline si nfigure s4 aan dd ,b an d e,an dc an df connec tpoint s representing thosechemica l compositionswhic h haveequa lvalue so fpv ,cp fan dorf ,respectively .I tca nb esee nfro m thesefigure stha tfat sar eth emos texpensiv e compounds toproduc e from FIGURE 4A 0.90 0.00 A 0.90 0.00
PV, NH
0.00 0.90 030
0.90 0.00 A 0.90 0.00 FIGURE 4 D
L60 0.30 PV NO
0.00 030 0.00 0.90 0.90 FRACTION CARBOHYDRATES0.6 0 0.30 0.00 «a 000 C.30 0.50 FRACTION FAT 030
Figure4 a an dd .Th eproductio nvalue s (pv)o fbiosynthesi so fbiomas s withvariou schemica lcomposition s fromglucos ewit h ammonia (4a)an dnitrat e (4d).Fo rfurthe rexplanatio nse etext . 0.90 0.00 A 0.90 0.00 FIGURE *B
CPF, NH
0.00 090 0.90
0.90 0.00 A 0-9° 0-00 FIGURE «E
0.60 0.30
CPF, NO
0.00 OJOO 030 0.00 0.00 0.30 0.60 FRACTION FAT 0.90
Figure 4b ande .Th e carbon,dioxid eproductio n factors (cpf)o f biosynthesis ofbioinas swit hvariou s chemicalcomposition s fromglucos ewit hammoni a (4b)an dnitrat e (4e).Fo r further explanationse etext . 0.90 0.00 A090 °-00 FIGURE *C BBS, *-8,
0.13
0.125 0.60 0.30> '0.60 0.30
ORF NH,
0.12
0.30 0.60> V0.30 0.60
v0.11
.0.105 v0.10 X NVO.095 X V0.09 0.00 0.901 ^0.00 0.90 —I— • 1 0.30 0.00 0.90 FRACTIONCARBOHYDRATE S 0.60 0.00 0.30 0.60 FRACTION FAT 090 >»
0.90 0.00 A 0.90 0.00 FIGURE 4F
ORF NO
0.00 0.00 0.90 0.90 FRACTION CARBOHYDRATES0 6 0 0.30 0.00 •* 0.00 0.30 0.60 FRACTION FAT 030
Figure 4c an df .Th eoxyge nrequiremen tfactor s (orf)o fbiosynthesi s ofbiomas swit hvariou schemica lcomposition s fromglucos ewit h ammonia (4c)an dnitrat e (4f).Fo r furtherexplanatio n seetext , 90 00 0.90 0.00 A 0- °- FIGURE 4G
RQ NH,
0.00 030 0.00 0.90 0.00 000 0.30 0.60 FRACTION FAT 0.90
00 0.90 0.00 A 0-90 ° FIGURE 4H
RQNor
0.00 0.90
FRACTION FAT
Figure4 g an dh .Th erespirator y quotients (RQ)o fbiosynthesi so f biomass fromglucos ewit h ammonia (4g)an dnitrat e(4h) . For furtherexplanatio nse etext . - 18-
glucose,an d thatprotei nsynthesi syield sonl yslightl ymor ewhe nnitrat e reductionoccurs .I freduce dnitroge ni savailabl ep vfo rprotei n synthesis isabou t5 0% higher .Th ecarbohydrate-ligni nmixtur ei srelativel y "cheap" tosynthesize .Fig .4 g an dh showth erespirator y quotient (molesCO _ producedpe rmol e0 ?consumed )fo rthes econversio nprocesses . Fig.5 indicate s theare ao fchemica lcomposition susuall y foundi n vegetativeplan t tissue,reproductiv eplan ttissue ,animals ,an dmicro organismsan d canb euse d incombinatio nwit hfig .4 a-h . It iseviden t thatpv ,cp fan dor f forthos e combinations of fractions inwhic hn onitroge ni sincorporate dmus thav esimila rpoint s inbot hset s offigures .A sa resul to f this,th eline s inth efig .4 d ,e ,f an dh representing thevalue s forth eglucos eplu snitrat esubstrate ,ar eturne d toth elef taroun dthei r fixedpoint so nth ehorizonta l axis,a scompare d toth eglucos eplu s ammoniasubstrat evalue s (fig.4 a ,b ,c and g). Most linesi nth efigure sprov et ob enearl yparalle lan dapproximatel y straight. Straightline sindicat e thatther ear en ointermediate s formeddurin g synthesis ofon ecompoun dan dutilize d inth esynthesi sproces so fanothe r compound.Suc ha for mo f "biochemical symbiosis"woul d increaseth eefficienc y ofth eoveral lproces s and causeth e lines tocurve :i tincrease sp v fora givenchemica lcompositio n abovetha twha tmigh tb eexpecte d inusin g straight lines,an dsimilarl y decreases orfan dcpf . Applying thedetaile d computation described abovet otissue swit h differentchemica lcomposition s isver y laborious anddifficul t totransmit . A computerprogra mha stherefor ebee ndeveloped .I ti swritte n inth e simulationlanguag eContinuou s SystemModelin gProgra man dwa s also translated intoFORTRAN .A cop y isavailabl eo nrequest . Becauseo f lacko fdata ,th echemica l compositionwithi neac ho fth e major fractions (table3 )i softe ntake nt ob e constant andonl yth e relative contributiono feac hfractio nt oth etota lvarying .Fortunatel y theresult so fth ecalculation s areaffecte d only toa smal lexten db y changesi ncompositio nwithi nthes efractions .I twa scalculate d forexampl e thatth evariable scharacterizin g theconversio no fglucos e into 12 differentprotein ssho wa muc hnarrowe r range (table5 )tha nth evariable s calculated forth emajo r fractions (fig.3) .Therefore ,a muc hsimple rwa y ofcalculatin g thevariable scharacterizin g theconversio nca nofte nb e used.Th eproces so fconvertin gglucos e intoon eo f thefraction sma y thenb e characterizedb ypv' ,cpf , orf andtw oadditiona l factors:th ehydroge n requirement factor(hrf )an dth eenerg y requirement factor (erf).Th efirs t 0.9D 0.00 « 0.90 0.00
0.00 0.90 00 0 0.90 0.90 FRACTION CARBOHYDRATES 0 SO 000 "*
Figure5 .Th evariatio ni nchemica lcompositio nwithi nan dbetwee n vegetative,no nstorag e tissueso fhighe rplant s (area1) , seedsan dstorag e tissues ofhighe rplant s (2),micro organisms (3)an danimal s (4).1 0% o f thebiomas si s assumed toconsis t ofmineral splu s organicacids .Th e compositiono findividua lorgan s canvar yove rwide rranges . Based ondat afro mth eHandboo ko fBiologica lDat a (1956) andHorowit z (1968). Table 5. Values characterizing theconversio nproces s ofglucos ewit h ammoniao rnitrat eint oprotein swit hvariou s amii^oaci d compositic_.$ ;th ecomposition swer e taken from theHandboo k ofBiologica lData ,1956 .
with ammonia wi th nitrate protein pv orf cpf pv orf cpf
albumin, egg 0.621 0.157 0.260 0.398 0.190 0.694 " , human serum 0.623 0.152 0.252 0.398 0.187 0.691 arachin 0.611 0.163 0.263 0.386' 0. 192 0.705 bacteriophage of E. coli 0.636 0. 1 72 0,253 0.399 0. 198 0.705 edestin 0.656 0.168 0.228 0.400 0.198 0.712 gliadin 0.638 0, 158 0.233 0.431 0. 184 0.633 gluten, corn 0.588- 0. 146 0.284 0.404 0. 174 0.653 " , wheat 0.664 0.163 0.217 0.426 0.194 0.665 insulin 0.626 0.164 0.247 0.402 0.196 0.683 papilloma, shope (virus) 0.635 0.166 0.254 0.397 0.198 0.707 ribonucle ase 0.673 0.183 0.233 0.413 0.210 0.710 zein 0.594 0.144 0.271 0.393 0.179 0.676 . -.— .-___— , - 19-
threewer edefine dearlie r (table 1);th eprim eindicate stha tthe .value s refert oweigh tratio sa tth estag ea twhic hal lmateria li sforme dfro m glucose,bu ta twhic hexces so rshortag eo fNADH „an dAT Pha sno tye tbee n removed.Hr fan der frepresen tth enumbe ro fmole so fNADH „an dAT Ppe r gramo fproduct ,respectively ,tha thav et ob eforme d (valuepositive) ,o r arerelease d inexces sdurin gsynthesis ^Hr fan der fca nlin k synthetic processeso fdifferen tfraction san dmus tb emad e zeroa tth een do fth e calculation:pv' ,cp f andor f thereforear eintermediat evalues * Table6 presents theirvalue sfo rth emajo r fractions.The ymus tb emultiplie db y thepar t that their fractionform so fth etotal ,an dthe nadde dtogether . Theenerg y required forth enon-syntheti c activitiesmus tb eadde dt oerf , and theadde dvalue so fth eenerg yan dhydroge nrequiremen t (etfan dhrf ) areadjuste dt ozer oa sdescribe d above.Tabl e7 give sa nexampl eo fthi s calculation.Sligh tmistake sar eintroduce dbecaus eC -fragment san dothe r intermediatesma yb eexchange dbetwee nth esyntheti cprocesse so fdifferen t chemical fractions.Thi si signore di nth esimple rapproach . Fromfig .3 i tfollow s thatsynthesi so ffat ,compose d asindicate d intabl e3 ,fro mglucos eca nb echaracterize db ya productio nvalu eo f
0.330.Fro mth e"molecula r formula"o fthi sfat ,C QAHI65°IO> tlieequatio n
1g glucos e- >0.51 5g fa t+ 0.41 0g 0 ,+ 0.07 5g H 20 canb ederive d (James,1953 )assumin gtha toxyge ni sformed .I fi ti s assumed thatoxyge ni sneithe rrelease dno rconsume d theequatio nbecome s
1.0g glucos e•* •0.37 2g fa t+ 0.40 8g C0 2+ 0.22 0g H 20
Iti sobviou stha tthes ever y simplecalculation s ignoremuc ho fwha t biochemistry teaches,an dgive serrorreousl yhig hestimate s ofconversio n efficiencies.O nth eothe rhan di tappear s thatapplicatio no fonl y superficialknowledg eo fend-produc t andsubstrat e compositionca nprovid e ausefu l firstestimat eo fth eyiel do fconversio nprocesses .
5.MODIFICATION S OFVARIABLE S CHARACTERIZINGA BIOSYNTHETI CPROCES S INDUCEDB YCHANGE SI NCONDITION S
Aspectso fbiosynthesi s requiringadditiona l consideration areth e compartmentationo fbiochemica lprocesses ,th efac ttha tdifferen tspecie s canutiliz e differentbioc^aaics'' .pathway st oachiev e thesam eend-product , andth epossibl eeffect s ox chzv.i~as in intarnalvariable s sucha sth eP/ 0 ratio,o ri nexterna lvariable s liketemperature . Table6 .Auxiliar yvalue s forcharacterizatio n ofa conversio nprocess , excludingcos t ofsubstrat e intakefro mth eenvironment .Fo r thecompositio no f thefractio n"nitrogenou s compounds"se etabl e3 .
pv orf cpf hrf erf amino acids with ammonia 0.700 0.0054 0*254 -0.01122 -0.00139 amino acids with nitrate 0.700 0.0054 0.254 0.02674 0.03899 protein with aEimonia 0.604 0.0052 0.252 -0.01285 0.03492 protein with nitrate 0.604 0.0052 0.252 0.03140 0.08197 nucleic acids with ammonia 1.072 0.0270 0,043 -0.01242 0.02793 nucleic acids with nitrate 1.072 0.0270 0.043 0.03484 0.07732 nitrogenous compounds with ammonia 0.620 0.0056 0.249 -0.01267 0.03108 nitrogenous compounds with nitrate 0.620 0.0056 0.249 0.03104 0.07754 carbohydrates 0.853 0.0 0.057 -0.00360 0.01224
lipids 0.351 0.0 0.471 -0.01010 0.05097 lignin 0.483 0.0444 0.244 -0.00431 0.01868
organic acids 1.104 0.0 -0.050 -0.01686 -0.00452 to T3 -f-1 CO CN r>. O m c\ CD CO 00 ai ess in CN CN cn cn U CD •-•v r- vO ~ — o r^» CO -H J3 CN —• o o o o CN eu 3 -u o o o o o o o r-4 cu cr* H C V«X » » • * • * • p* ^~» Q H 0) O >. o o o o o o o H •—^ *—S /—S <<-». *•— .g <; vi iw co 1 •< cn m r~- cn •—• «w* vy •>«• "w» •x* sf
5.1. COMPMTMENTATION
Compartmentationha s twoaspects :th eplac eo f synthesiso fa compoun d mayb edifferen tfro mth eplac eo f "destination",an d anexces s ofATP , NADHLo ra nintermediat etha ti sproduce di nexces si non eplac ema yno tb e available fora deman delsewhere .Tw oexample so f thefirs taspec tca nb e given.Th ecel lwal lconsist smainl y ofpolysaccharides ,bu tofte nals o includes ligninan dproteins .Th ecel lwal li ssituate doutsid eth ecytoplasm , sotha tit sbuildin gblock sar eeithe rexcreted ,o ractivate dan dpolymerize d onth eoutsid eo f themembran eenvelopin gth ecytoplasm .I ti sassume d that all ligninmolecule s aresynthesize di nth ecytoplas man dexcrete d ata cos t of 1AT Pmolecul epe rconiferyl-alcoho lmonomer ;tha tn oprotei n isexcreted , andtha t5 0% o fth ecel lpolysaccharide s isforme d fromglucos etha tdi d notente r thecytoplasm ,whil e theothe r5 0% i sforme d andremain s inth e cytoplasm. Themajorit y ofsyntheti cprocesse soccu ri nth ehyaloplasm , (the cellplasma ,embeddin gth ecel lorganelles) ,whil esom eoccu ri nth e mitochondria,mos to fwhic hi sfatt yacid ssynthesi s (Bielka, 1969).Withou t muchevidenc ei ti sassume dtha tonl y fatty acidsar esynthesize d in mitochondriaan dar e translocated intoth ehyaloplasm ., an d thatal lothe r eventsoccu r inth ehyaloplas m .1 AT Pmolecul ema yb erequire d to translocate 1fatt yaci dmolecul e fromth emitochondrio nint o theplasma . Only thesetw ocase so fcompartmentatio nar einclude d inth ese to f standardcondition s forcalculation s (table 4).I tmus tb erealized , however,tha tthes erefinement s decreasep vonl yb yabou t 1% . Thesecon daspec to fcompartmentatio nconcern s synthesis inisolate d cellcompartment so ra tdifferen t times,s otha texchang eo fintermediate s withothe rprocesse so rtranspor to fth eend-produc tdoe sno toccur .I f synthesiso fdifferen tcompound s occurswit hspatia lo rtempora l separation whilen oexchang eo fenerg y ofhydroge n takesplac e thevalue s ofer fan d hrfmus tb emad ezer obefor eaddin gpv' ,or f and cpf, thereby decreasing theyiel dan defficienc y ofth eoveral lprocess .
Separationo fth eNADH 2poo li nhyaloplas man dmitochondri a isknow n toexis tan dt ob eeffective .However ,b y transferringH L fromNADH _ to oxalo-acetatei nmitochondri aa compoun di sforme d (malate)whic hpasse s the membraneeasily ,whil ei nth ehyaloplas m thehydroge nca nb etransferre d toNA Dan d theoxalo-acetat e formeddiffuse sbac k toth emitochondri a (Bielka, 1969).A syste mwher eexchang ei sfacilitate db y carrierswithou t supplyo fadditiona l energyca nb e regarded asfre eexchange .Compartmentatio n - 21-
inthi scontex tmus t thereforeb edefine d asth eseparat io no f spaces betweenwhic hn opassiv e transport takesplace .Th esiz eo f compartmentsi s notequa l foral lmolecules .Fo rwate rmolecule s thecompartmen t exceeds thecell ,fo rpyruvat ean dmalat eth ehyaloplasm ; andmitochondri aar e equivalent,whil e forman ymolecule s thehyaloplasm.. ,vacuol ean d mitochondria areseparat ecompartments . Separationo fprocesse si ntim eoccur s commonly.Secundar ycel lwal l thickeningi nplan t cells,fo rinstance ,occur si ncell swit h "fullygrown " protoplasma,an dals olipid so raromatic sar esynthesize dmainl y in maturecells . Itha sbee nsuggeste d (Lardy andFerguson , 1969)tha tcell sstor e energy asosmoti cenerg yb yaccumulatio no fion s inmitochondri a and that thisma ybecom eavailabl ea sAT P ina revers eprocess .Suc ha proces s can linkenergy-yieldin g andenergy-consumin g reactions separated intime ,bu t becauseo f thesmal lvolum eo fmitochondria ,i ti sprobabl y unimportant forth eyiel do fbiosyntheti cprocesses . Thevalue so fpv ,or fan d cpffo rsynthesi so fstandar dplan tbiomas s andbacteri aar eshow ni ntabl e8 ,assumin g thatth esi xmajo r fractions eitherd oo rd ono texchang eenerg yan dhydroge ndurin g theirsynthesis . Thisaspec to fcompartmentatio nprove s tob eunimportan t forbiosynthesi s ofplant san dbacteri awhe nnitrat e isth enitroge nsource ,bu tnoticabl e ifammoni ai ssupplied .
5.2.ALJERNATIVE_PATHWAY S
Thesimilarit ybetwee nanaboli cprocesse si norganism s isappreciabl e andfacilitate scalculation s enormously.I nsom ecases ,however ,differen t speciesus edifferen tpathway s todegrad eo r synthesizeth esam eproduct , (Dagleyan dNicholson , 1970).Th edifferenc ebetwee nbot hma yb esmall , asfo rornithin e (table2 )o rlarge .Fo r anexampl eo f thelatter ,oxalo aceticacid ,a nintermediat e inman y reactions,ma yb e formedb y glycolysis andth eglyoxylat ecycle ,yielding :
1glucos e+ 3 H 20•* •1oxal oaceti caci d+ 2 C O +2 AT P+ 7 NADH - (table2 ,pathway s 140an d 508), orb y thecarboxylatio no fpyruvate ,yielding :
0.5 glucose+ C02 •*• 1oxal oaceti caci d+ 1NADH - (table2 ,pathway s 140an d 505).Th eamoun to fsubstrate s differb y afacto r 2.Synthesi svi acarboxylatio nrelease s littleNADH- ,wherea s synthesisvi a otherpathway syield s considerablymore .Th eexces so fNADH 9wil l generally Table 8. The effect of compartmentation of biosynthesis of plant dry matter and bacteria biomass. For the chemical composition of plant biomass and of the fractions see table 3• The composition of bacteria was assumed to be Q.6I g/g proteins, 0.17 g/g nucleic acici 0.12 g/g carbohydrates, 0.07 g/g lipids and 0.03 g/g minerals. For further explanation see text.
pv orf cpf compartmentation glucose+ ammoni a-> •plan tbiomas s 0.746 0.103 0.179 no glucose+ ammoni a• >plan tbiomas s 0.735 0.116 0.197 yes glucose+ nitrat e-* •plan tbiomas s 0.650 0.123 0.343 no glucose+ nitrat e•* •plan tbiomas s 0.645 0.130 0.352 yes glucose+ ammoni a-> •bacteri abiomas s 0.651 0.143 0.266 no glucose+ ammoni a-* •bacteri abiomas s 0.644 0,154 0.280 yes glucose+ nitrat e-* •bacteri abiomas s 0.449 0.177 0.637 no glucose+ nitrat e •*•bacteri abiomas s 0.448 0.638 yes - 22-
beuse d inothe rreactions ,whic h sparesothe rsubstrat emolecule s from beingoxidized .0. 5 glucosemolecul erelease s incombustio n (glycolysis andTC Acycle )6 KADH „an d 1 ATPmolecules ,s otha t thedifferenc ebetwee n bothpathway s isonl y JATP .Thus ,i fth eoveral lproces srequire smor e ATP orNADH - thani srelease ddurin gsynthesi s thechoic ebetwee npathway s 508an d50 6 (table2 )hardl yaffect s thep vo fth eprocess .If ,however , alloxalo-aceti caci di sforme dvi ath efirs tpathwa yan dmuc ho fi ti s synthesized anNADH _ overproductionma yoccur .Withou t furtherevidenc ei t isassume d thatth ecel lregulate s itsmetabolis mi nsuc ha wa y thati t switchesprocesse st oth e"cheapes tpathway" ,i fonl y littleo fth eenerg y excessca nb euse delsewhere .A regulationo fth eactivit y ofsyntheti c pathwaysaccordin g toth eneed so fth ecel lwa ssuggeste db yexperiment s ofBrow nan dWittenberge r (1971)an dma yoperat evi a the "energycharge " ofth ecel l (thesu mo fth ehig henerg yphosphat ebonds :2 i nAT Pan d 1i n ADP,se eAtkinson , 1968)o rth eNADlWNA Dratio .O nth eassumptio n thata mechanismo fthi skin dexists ,th esimples twa y toaccoun t fori ti st o calculatea sthoug hth e"cheapest "pathwa y isalway s taken,unles sther ei s counterevidence . Inconclusio ni tca nb e stated thatth eeffect so fusin g alternative pathways onth evalue scharacterizin g theconversio nar egenerall ysmall . Becauseo fth esimilarit yo fmetabolis m invariou skind so flivin gorganism s iti slikel y thatth econversio ncharacterizin gvalue sd ono tdepen do nth e speciesconsidered .
5.3.EFFECT_0F_THE_P/0J3LATI0_gN_PY A_CPF_AND_ORF
Foraerobi c growth,wit hwhic h thispape ri sconcerned ,th enumbe ro f ATPmolecule s formedpe rmolecul eNADE L oxidized (theP/ 0ratio )an dpe r moleculeo fglucos ei simportant .Thes evalue shav ebee n takent ob e 3an d 38,respectively .Whe nth eP/ 0 ratioi saltere dth eamoun to fsubstrat e required forAT Pproductio nchanges .Fig .6 arepresent s therelationshi p betweenth evalue scharacterizin g theconversio no fglucos ewit hnitrat e orammoni aint o"standar dprotein "wit h theP/ 0 ratio asvariable ,an d fig.6 brepresent sth esam efo rgrowt ho f "standardplan tdr ymatter" . A semilogarithmi c scalewa suse d toobtai nhighe rlegibility .Value sa t theunrealisti cP/ 0rati oo f 10 areinclude d tosho who wmuc h substrate isuse dfo renerg yproductio n atth evariou sP/ 0ratios . V. V. 1.2 - ">. >N. *-» FIGURE "^. CPF PV,CPF N ^>.NOJ AND ORF 1.0 s. "** \ "V
v XCPF % N NH3 \ 0.8 v N "* -^ V 0~- •s
0.6 - XN ^s N \ 0RFNH>. X N
0.4 - ^•^ X K ,. _--—— jS^ N ^l*^"^ ---^ % ^ NH _^"^ 3 ^^> <\ "-- •V V N. V S N 0.2 *» **%w K* ^-**vV _ _^—-"""^ N03
| _| OJO 1 1 1 L. 6 0.1 02 03 0.6 1.0 20 X0 " 10 P/0 RATIO
1.0 FIGURE 6B PV,CPF AND ORF
3.0 ' 106 P/O RATIO
Figure 6 a and b. Conversion characteristics for protein biosynthesis (6a) and biomass biosynthesis (6b) from glucose at various P/0 ratios. - 23-
Fromfig .6 bi tappear s that thep vo fbiosynthesi s of "standardplan t biomass"i shardl yaffecte db y theP/ 0rati obetwee n2 an d 3.Th eefficienc y ofsubstrat econsumptio nfo rprocesse s like transportan dmaintenanc e is proportionalt oth eP/ 0 ratio.I tma y thereforeb eexpecte d that although inrapidl y growingplant s theeffec to fa chang e inth eP/ 0 ratioi ssmall , iti so fincreasin gimportanc ewit hdecreasin grelativ egrowt hrates . Fig. 7arepresent s theeffec t ofth eP/ 0rati oo nth eamoun to fprotein ,an d fig. 7bth eeffec to nth eamoun to f "standardplan tdr ymatter "forme da t variousrelativ e growthrates ,assumin ga nenerg yconsumptio no f0.0031 7
gmolAT P (0.015g glucose )pe rgra mdr ymatte rpe ru ay forstructur e maintenance (cf.Pennin gd eVries,1974b) .McDanie l (1969)an dother s attributed a largeheterosi seffec ti nseedling st oa nimprovemen to fth eP/ 0rati o from2. 0 to2.5 .Thi sincreas ewa squestione db yElli s etal . (1973),bu t eveni fi ti sreal ,fig .7 bindicate s thati ti simprobabl e thatsuc ha smallincreas ei nP/ 0rati oi sdirectl y responsible forth eyiel d increase observed. LowP/ 0ratio sar ecommonl y reported forcel lfre eextract so fmicro organisms (Stouthamer, 1969;Va nMeyenburg , 1969),bu tmeasurement s in livingcell syield svalue so fapproximatel y3 (Hadjipetrou etal. ,1964 ; Hempfling, 1970;D eVrie s etal. ,1970) . Inhighe r animals andi nplan t tissues theP/ 0 ratioi smostl y found tob e3 (Beevers,1961 ;Pullma nan d Schatz, 1967).Unde rcertai ncondition scell sca nproduc emor eAT Po r NADH.Jtha nthe yconsume ,fo rinstanc edurin g rapidbreakdow no ffatt yacid s incotyledon so fgerminatin gpeanuts .Unde r thesecondition s thecel lmus t limitAT Pproduction ,resultin gi na lowerin go f theP/ 0ratio .
5.4. TEWEMTyj^_ANp_0TffiR_E^^
Therei sn oevidenc e that theP/ 0rati oi schange d ortha t alternative syntheticpathway sar eutilize d at different temperatures,o runde r different levelso fwate rstress .Thu spv ,cp fan dor far etake na sindependen to f temperaturean dwate rstres sove rth erang eo ftemperatur e andtissu ewate r potentialsnormall yencountered .Experimenta levidenc eha sbee npresente d (Penningd eVries ,1972 ,1974a )that ,i ngerminatin g seeds and growing plants,temperatur edoe sno t affectth erat eo fconversio n ofsubstrat e intoend-product ,an d thusth erat eo frespiration ,bu t therelatio no f growth torespiratio nan dsubstrat econsumptio nremain sunaffected . 10 -
BIOMASS (grom) FIGURE 7A
0.8
0.6
2.0 3.0 P/O RATIO
BIOMASS (gram) FIGURE 7B
--ii.---*5»V!5' *"— — """ "-'"" "
2.0 3.0 P/O RATIO
Figure7 a andb .Th eyield so fgrowt hprocesse s ing protei n (7a)o r gbiomas s (7b) perg glucos e (withammonia ,hydroge nsulfid ean dminerals )a tvariou s P/0 ratios andrelativ e growthrate s (units gg day ). 24-
Duet otemperatur echange sth echemica l composition ofgrowin gmateria l maychang e (Udakaan dHoriutchi ,1965 ;Jone san dHough ,1970 ;Schweye nan d Kaudewitz,1971 )whic hchange s thepv .Thi s isa nindirec teffec to f temperature,an di ssmal li nth ecase sreported .Typ ean dquantit yo f substrateinfluenc estrongl y thenitroge nconten to fAspergillu snige r (Terroinee tal. , 1922).Growt hcondition s affect thechemica l composition ofalga econsiderabl y (VanOorschot , 1955),an d thesalinit yo f themediu m maychang e thecompositio nt oa smal lexten t (Reistad, 1970).
6.MAINTENANC EO FCELLULA RSTRUCTURE SAN DOTHE RRESPIRATIO N PROCESSES
Although iti scommo nknowledg e thatlivin gcell shav e aminima l rate ofmetabolis mwhic h isnecessar y tomaintai n theirstructur e inth eactua l condition,littl ei sknow nabou t thetyp ean drat eo fmaintenanc eprocesses . Therat eo fthes eprocesse swa sestimate d inhighe rplant st orequir e 1- 4% ofth edr ymatte rpe rda y tob eoxidize d (Penningd eVries ,1972 ,1974b) . Idlingrespiratio nha sbee nsuggeste d tob ea sin kfo rassimilate s inplan t tissue (Beevers,1970 ;Tanaka , 1972).Whe n itexist s iti ssubstrat e oxidationuseles s toth ecell ,unles s itindicate s thepresenc eo fa n aspecto frespiratio ntha tha sbee noverlooke d inthi sapproach .I twa s shown(Pennin gd eVries ,1972 ,1974a ) thatexperimenta l resultswit hhighe r plantsca nb eexplaine dcompletel ywithou t assuming thepresenc eo fidlin g respiration.A comparisono faccurat erespiratio nmeasurement swit h theoreticalrate so frespiratio n causedb yconversion ,transpor tan d maintenancei son emean so fdetectin g theexistenc eo f idlingrespiration . Photorespirationo fgree nleave si nth eligh tdiminishe s thene t rate ofassimilat eproduction ,bu tdoe sno tinterfer edirectl ywit h theconversio n processeso fassimilate s intobiomass .Thus ,photorespiratio nma yb eregarde d asa proces stha tonl ydecrease s theefficienc y ofligh tutilizatio nfo r productiono fassimilate s (Penningd eVries , 1974a).
7.CONCLUSION S
Iti spossibl et ocomput efro mbiochemica ldat ath eamoun to f substrate required tosynthesiz e 1.00gra mbiomas so fa specifie dchemica l composition andth esimultaneou s oxygenconsumptio nan d carbondioxid eproduction .Thi s approacho fbiosynthesi san d growthi sver ypowerful ,a s thechemica l compositiono fsubstrat ean dend-product ,th eparticula rbiochemistr y of theorganis man dals oth enon-syntheti cactivitie s duringbiosynthesi s can - 25-
be takenint oaccoun ti npredictin g thedr ymatte rproductio n froma give n amounto fsubstrate .I tgive sa ninsigh tint oquantitativ e aspectso f growthprocesses ,sinc ei tconsider s allimportan tpart so fth etota l separately,an di nrelatio nt oeac hother . Numerousbiochemica lpathway sar edescribe d inmicro-organisms ,bu t notman yhav ebee ndetermine d inhighe rplants .However ,i ti sno texpecte d thatver y differentsyntheti cpathway swil lb ediscovere d (Dagleyan d Nicholson, 1970).A sdifference sbetwee npathway s toobtai na particula r product froma give nsubstrat ear eusuall y small,unfamiliarit ywit h specific aspectso fplan tbiochemistr y seems tob ea smal lhandicap .Muc hmor e importanti sth elac ko fknowledg e aboutth eenerg y requirements for cellularprocesses ,suc ha smembran e transport,compartmentatio nan denzym e maintenance.I nth ecalculations ,membran etranspor twa s found tob e relatively important,an dth eenerg yrequiremen t for "toolmaintenance " lessimportan t (fig.2 aan d b); compartmentationha s itslarges teffec t whennitroge ni ssupplie da sammoni a (table 8). Fewusefu lbasi cdat ai n thesefield scoul db e collected fromliterature .Th einaccurac y ofth e numericalestimate s forth ecos t ofthes eprocesse s contribute considerably toth einaccurac y ofth een dresult so fth ecomputations .Often ,th eP/ 0 ratioi sanothe runknown .Wherea s iti sgenerall yagree d that theP/ 0 ratio inhighe rorganism si s3 o r closet othi svalue ,thi srati oca nb e considerably reducedb yuncouplin gagents .I ti sshow n (fig.6 an d 7)tha t areductio ni nP/ 0 ratiofro m3 t o2 cause sa yiel d reductiono fabou t5 % athig hrelativ egrowt hrates .Th esmalle r therelativ eyiel d growthrate , themor eimportan t theP/ 0 ratiobecomes . Suitabledetermination s ofbiomas scomponents ,includin gnitrogenou s compounds,carbohydrates ,fats ,lignin ,organi cacid san dminerals ,ar e scarcean dstandar dmethod s todetermin e thesefigure s areno tavailable . Thisi seve nmor e truefo rth eamin oaci dcompositio no f theproteins ,th e differentsugar si nth ecarbohydrat e fraction,etc .Bu tknowledg eo f the amountso fth emai n fractions iso fmajo r importance,a svalue s characterizing aconversio nar equit edifferen t forth emai nchemica lfraction s (fig.3 , table 6), andmuc hmor esimila rwithi nthes e (table 5). Lacko f information onth echemica lcompositio no fth een dproduc t isofte n themajo rcaus eo f inaccuracyo fth een dresul to fth ecomputations . Anattractiv e featureo f thisapproac ht obiochemica lproductio n processesi stha tth eweight so fth erequire d co-substratesan dby-product s areobtained ,a swel la sth eweight so f themai nproduc tan dprincipa l - 26-
substrate.I twa sshow ntha tbiosynthesi s andrespiratio nar erelate di n apredictabl emanner .Respiratio nmeasurement sca nb eperforme dwithou t disturbing thegrowin gorganism ,an dth erat eo f growthca nthu sb e determined fromth erat eo frespiration .Fo rman ypurpose s thismetho di s moresuitabl e thanth emetho d formonitorin gplan t dryweigh t increaseno w commonlyused ,whic hi sbase dupo ndestructiv e determination ofth eweight s ofessentiall y unrelated samplesa tsuccessiv emoment s intime .Henc e studieso ngrowt han drespiratio nca nprofi tfro mthi sapproach . Thisapproac h tobiosynthesi sma yb e called simulation,definin g simulationa sth eimitatio no frea lprocesse susin gsom ekin do f amode l (cfD eWit ,1970) .Simulatio nb y thisdefinitio n comprises anumeri c imitation ofth etype san dquantitie so f thematerial s converted ando fth eenergeti c aspectso fal lrelevan tprocesses .Dynami c simulationo fgrowt ho na biochemicalleve lmus tinclud e theconcentratio no fAT P incells ,whic h controls therat eo freaction san di sitsel f changedb y thesereactions , andmus taccoun tfo rth einhibitin go rstimulatin gactio no fsubstrate , end-product andregulatin gmolecules .Al lrelevan tconcentration s arethe n continuously computed.I ti seas y toconceiv etha tdynami csimulatio n requiresfa rmor edetaile dknowledg e thani savailabl ewit hrespec tt o suchrelationship s asth eactivit yo findividua lenzyme san d themanne r inwhic henzym eactivit yvarie swit hchange s inAT Pconcentration ,end - productleve lan denvironmenta l factors,bu tknowledg e aboutregulator y mechanisms israpidl y accumulating.Attempt so fa limite d scopema yb e veryuseful ,sinc ethe yindicat e gapsi nou rknowledg e andspecif y the typeo fdat arequire d fora bette runderstandin go fth ewhol esystem .I n completedmodels ,system sbehaviou rca nb estudie d and theimportanc eo f particularelement si nth etota lsyste mrecognized .Fo rsmal l subsystems likemitochondri ao r theKrebs-cycle ,enoug hinformatio nha sbee n collected anddynami csimulatio nreporte d (Garfinkel,1970 ;Garfinke le t al., 1970). Thesimulatio nmode ldiscusse dher ei sno ta mode l fordynami csimulation . Thechemica lcompositio no fth eend-produc tis ,therefore ,no t aresul to f thissimulation ,bu t aninpu tfo rth ecalculations .However ,i tseem s asthoug ha firstattemp tca nb emad et oconstruc ta complet emode l for simulating theconversio no fal ltype so forgani c substrates intoeac h productrequired ;th emode lpresente d doesthi sonl y forth esubstrat e glucose. - 27-
ACKNOWLEDGEMENTS
Theautho r thanksDr .W .Dijkshoorn ,Dr .A.J.H .va nEs ,Dr .M.G . Huck,Dr .A.H .Stouthamer ,Dr .J.H.M .Thornley ,Drs .N .Vertreg tan d Dr.C.T .d eWi t forth evaluabl ediscussion s and theirpositiv ecriticis m onthi smanuscript ,an dMis sA.H .va nRosse mfo rcorrectin g theEnglis h text.Mis s C.G.va nGulij k typed themanuscrip tman y times,an d Ir C.d eJong etranslate d theCSM Pprogra mint oa FORTRA Nprogram .
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F.W.T.Pannin gde.Vrie s
.Departmento fTheoretica l ProductionEcolog y
Agricultural University
Wageningen
In:Photosynthesi s andproductivit y
indifferen tenvironments ,
(IBPPhotosynthesi sMeetin g
Aberystwyth,Apri l 1973),
CambridgeUniversit y Press,1974 . Summaryan d introduction ->n.T- - ••* • I, ir • -L , -i ii .., ••••,• Iti sexplaine dbriefl yho w tocomput e thequantitativ e relationbetwee n substrate consumption,,dr ymatte rproductio nan d respirationwhe nsubstrat e andproduc t arechemicall ywel ldefined .T ocomput edr ymatte r increaseo f plants,th echemica lcompositio no f theen dproduc tmus tb edetermine d analytically and thequalit y and amounto fsubstrat e specified.Analysi s of phloemcontent s shows that theorgani c substrate forgrowt h consistsmainl y ofsucros e andamin o acids,whos ebiosynthesi s isclosel y linked.Thus ,tota l plant CO-assimilatio n is,alone ,no t asufficien tbas e fromwhic h tocomput e growth,an dnitrat e reduction,amin oaci d synthesis andothe rprocesse smus t alsob econsidered :neglectin g thesema yunderestimat e theyiel d froma givenamount ,o f C0? assimilated up to3 0% .Thes e subjects areelaborated ,an d theconsequence s forth e interpretation ofCO~~assimilatio nligh t response curves arediscussed .Maintenanc e ofbiomas san d translocation of assimilates throughphloe mvessel s alsous eassimilates ,bu twil lno t beconsidere dhere , mainly forreason so funcertaint y about theunderlyin gmechanisms .
Anexperimenta l approach to therelatio no fCO^-assimilatio nt ogrowt h
From the "molecular formula"o f thebiomas sproduced'th e relationo f netC O-assimilatio n tobiomas s increase iseasil y obtained:whe n the"molecula r formula"i sC„.H, „0, N_ itfollow s fromth e "molecularweight "an dth e 86 f!604 5r 7 ° fractiono fcarbo n that.1.0 0gra mbiomas s is formed from 1.88gra mC0„ .Th e netcarbo nassimilatio n correspondswit h thedr yweigh t increase,irrespectively ofth enatur ean defficienc y of theprocesse s that occur.Th eefficienc y of carbonutilizatio nseem s 100% ,becaus eC0 „ lossesar emasked .
Thisprocedur e isver y simple incas eo falga e continuously exposed to sufficient light.Whe nperiod s of light anddarknes s alternate,th eC O- assimilation inth e light and dissimilation indarknes s mustb emeasure d to determine thedail yne t C0?-uptake.Again ,fro m thisvalu e and theelementar y compositionth eweigh t of thebiomas sproduce d canb e calculated. Inhighe r plants thesit eo fCO--assimilatio n isremove d fromth esite swher e growth
occurs,an d theperio d forsubstrat eproductio n (CQ~~assimilation)i sshorte r
than thatfo rsubstrat e consumptioni ngrowth .Nevertheles s the rateo fdr y matterincreas e canb e calculated from thedail yne tCO„-uptak ean dth e elementary composition,bu t thisknowledg e iso f smallpractica lvalue .
Empirical aquationsma yb euse d tocalculat e thebiomas syiel d and respiration fromth egros s assimilation,bu tsinc e theunderlyin gmechanis m isno tknow n suchequation s cannotb e applied inothe r conditionso r toothe rspecie s
(McCree, 1970). Toobtai n an insight intoth e relationbetwee ngros s assimilation andbiomas syiel d and respiration indifferen t situationsa more fundamentalapproac h isrequired .
Theter m "biosynthesis"wil lb euse d torefe rt oformatio no fdr ymatter , and "growth"t o totaldr yweigh t increase,includin gbiosynthesi s and maintenance.
Abiochemica l approach toplan tbiosynthesi s
Detailed analysis ofth ebiochemica l andcellula r processes occurring ingrowin gcell senable scomputatio no fyiel d and gasexchang e forth e conversiono fglucos e intoplan t drymatte r indarkness .Bot hyiel d andga s exchangedepen do n thechemica lcompositio no f theen dproduc t (Table1) .
Energy requirements formaintenanc e ofensym eactivit y anduptak eo f molecules throughmembrane s arene twel lknown ,bu tresult so f such computations areofte n little affectedb y roughestimate s of these costs (Penningd e
Vriese tal. , 1973).
Thesubstrat e for growth inplant s consists ofmono -an ddisaccharides , aminoacids ,organi c acidsan dothe r specific compounds (e.g.Kursanov ,
1963). Thismake s computation of the.yiel dan d gasexchang eo f growthmor e complicated,bu tdoe sno t add amajo rdifficult y as longa s the substrate . - 3-
composition isknown ,an d themos tefficien tus eo f thesubstrat e ismade .
Forbiosynthesi s of 1.00 gratalea fdr ymatte r 1.36gra mo fa mixe d organic
substratei srequired ;formatio no forgan swit h differentchemica l
compositions requires otheramounts ,example so fwhic h are given inTabl e2 .
Iti simportan t tonot e that thenumber sgive n inTable s 1sra d2 ar e
independento ftemperatur e and.species ,an dar edetermine d only by the
compositionso fsubstrat e anden dproduct .
Translocationo fsubstrat e in thephloe mi sa nactiv eprocess .Onl ya negligible fractiono f thetranslocate d assimilates isconsume d toprovid e
energy for translocation overshor tdistance s (Kursanov, 1963;Weatherle y &
Johnson, 1968;Aikraa n &Anderson , 1971),bu t theintegrate d costs for transport overmeter sma yno tb enegligible .Cost so f translocationwithi n thephloe m
areno tconsidere dhere .Loadin g andunloadin g thephloe mwil lb e treated separately.
Iti sconclude d that therat eo fbiosynthesi s canb epredicte d fromth e•
rateo fsubstrat e supply togrowin gpoint san d thechemica l compositiono f
thebiomas s formed.Th e rateo f substrateproductio nb y leaves iseasil y obtained fromth eCO„~assimilatio nligh trespons e curvean d incidentligh t intensity ata 10% accurac y level,bu ta precis e calculation containssom e pitfalls.
Aplan tphysiological-biochemica l approach tobiosynthesi s a.C0 9~assxmilation_and_ghctos^nthesis
Ingrowt hsimulatio nmodel s iti sgenerall y assumed thatal l assimilated
CO-molecule s areconverte d intoglucose ,an dtha t glucoseplu smineral sar e theonl y substrates forgrowth .Thi si sa nover-simplification ,becaus e in irradiated leavesver y often otherenerg y consumingprocesse s occur simultaneouslywit hCO„-reduction .Th e reductiono fNO.. ,th e subsequent formationo famin oacids ,an d theloadin gth ephloe mar e themos t important _4 -
of theseprocesses ,whic h areno t detectedb ymeasurin gCO--uptake .Mos to f theNO--reductio no fagricultura l cropplant soccur s inth e light ingree n leaves (Beavers &Hageman , 1969;Bornkamm ,1970 ;Hewitt , 1970). In thesecase s photosynthesisingcell sconsum emor eenerg y thani scalculate d fromreductio n ofth eassimilate d C0o toglucose .Still ,no tai lassimilate dCO - isreduced : foreac hmolecul eo freduce dNO -on eorgani c acidmolecul ei sforme db y carboxylatingpyruvate .Th esalt s of theseacid s remain inth e leaves insom e species,bu tabou thal f istransporte d to theroot s inother s (BenZion i et al., 1971;Dijkshoor n &Ismunadji , 1972),wher e theorgani c acid isconverte d intopyruvat ean d theC0 „ reformed isexchange d withK0 „ fromth eroo tmedium ,
N0„reductio nbein gaccompanie d by aC0 „ flux through theplant .
Determination ofenerg y absorptionb y leaves viameasuremen to f0 - evolutioni sbette rtha nvi aC0--uptake ,becaus e itaccount s forN O-reductio n andcarboxylation .But ,fo rinstance ,loadin go fth ephloe mconsume senerg y withoutexchang eo fmolecule swit h theenvironment ,an dcanno tb edetecte d bymeasurin gga sexchang e (Ried, 1970).Eve ni fi twer epossibl e todetermin e accurately leafenerg y absorption inchemica lprocesse s (includingti-anspor t processes)b ymeasurin g the totalenerg y absorptionan dsubtractin gth e energy lostb y thermalreradiatio nan d transfero fsensibl e and evaporative heat loss,th eactua lenerg y absorptionwoul d stillno tb emeasured .Firstly , because inprimar y chlorophyllreaction smor eenerg y isabsorbe d thani s retained inglucose ,bu t since glucosei sth estartin gpoin tfo rbiochemica l conversion calculations there isn onee d toconside r energy lostbefor e this point.Secondly ,becaus e theenerg y retainedi nprocesse s thatoccu ri n addition toC0„-reductio ni ssmalle r thanth eamoun t ofenerg y required to execute them.Simultaneou s energy consumingprocesse s in the leafar e probably competitive,s o thata t lowligh t intensities therat eo fC0- - reductioni sreduce dwhe n therat eo fNO -reductio n increases,a sshow n experimentally byBonger s (1956)wit h algae.A thig h light intensities,wher e therat eo fC O-diffusio n limits theassimilatio n rate,thes e additional 5-
energy consumingprocesse s occur freeo fcos t for theplant .I twa s shown byDijkshoo m &Ismunadj i (1972)tha tric eplant s suppliedwit hN0 « athig h
light intensities growa s fast aswit hNH~ ,bu t suchexperiment smus tb e interpretedwit h care,sinc e theplan t compositionma yb e changed,thereb y changing therelatio nbetwee nC0 „fixatio nan ddr ymatte rincrease .
Suchconsideration s indicate thatphotosynthesis ,CCL-assimilatio nan d conversionprocesse smus tb e considered inthei rphysiologica l context.Onl y whenth e informationi savailabl e ast owhic hprocesse s occur inth e leafan d atwha t rateca nth emeasure dC0 0-assimilation light response curveb e extrapolated toa rang eo f conditions inwhic h itwa sno testablished .CCL - assiaiilationligh t responsecurve s are fairlywel lknow n forman yspecies , especially agriculturalplants ,bu t little information is availableo nth e rate ofNCL-reductio nan d substrateexpor t from leaves throughout theda y in field situations ori nparticula rexperiments .A naverag e rateo fNG„-reductio i during theda yca nb eobtaine d analytically,bu tth eactua lrat ema yvar y with lightintensit y (e.g.Bongers , 1956)an d incubationperio d (e.g.Travi s et al., 1970).A tpresent ,onl y instead y statecondition swhe n therat eo f allprocesse s canb ederive d fromth eC0„~uptak erate ,ca ncalculation sb e performedwit h someaccuracy .
Photorespiration decreases thene tC0 2~reductionrat eo fa nirradiate d leaf.I tdoe sno t contribute toan y substrateproduction ,an ddoe sno tprovid e energy toan yactiv eproces s thatcanno tb e otherwise performed (Beevers&
Bjorkman,i nCanvin , !970).O na cellula r level,photorespiratio nma yb e useful inprovidin greductio nequivalent s toth ecytoplasm ,wher e thesear e used instead ofmitochondria l products (Tolbert, 1971).Fo r growth predictions photorespiration canb e seena s a.facto r thatdiminishe s the rateo fC O- assimilation,lik e lowtemperature s orVatmosphericCO„~concentrations . - 6-
Aparticula rstead y stateconditio nma yb e considered inorde r toverif y
thepredicte d dissimilation rate against ameasure d rate ofCO^-assirailatio n
(substrateproduction) .Maiz eplant swer egrow n ona nutrien t solutiona t
20 to2 5C an da ta ligh t level of 70J m sec .Whol e plants of 10t o
24day sag ereceive d 3periods.o f 7hour s light ofon e intensity,eac h
followedb y 1hou rdarknes s ata relativ ehumidit y of 85% .Durin gA -2-1 subsequent days light intensitieswer e applied up to30 0J m sec .Th e
rateo fCO^-assimilatio nwa smonitore d continuouslywit h the assembly described
by Louwerse &Va nOorscho t (1969).A t theen do f thethir dperio d therat eo f
netassimilatio n anddissimilation ,measure d inth enex thour ,ar ei n
"equilibrium'8,a swa sconclude d frompreliminar y experiments,unles s therate s
inth eol dan dne w "steady state"ar ever y different.I nthi s "steadystate "
the amounto fcarbo nassimilate d in7 hour s isequa l toth eamoun to fcarbo n utilized in8 hour s forconversion ,transpor t andmaintenance .Th erelatio n between the amountso fC0 „assimilated ,dr ymatte rproduce d andC0 „ formed
inthes eprocesse s forthi sparticula r "steady state"experimen twil lb e
computedbelow .Essentiall y similarexperiment shav ebee n reported elsewhere
(Penningd eVries , 1972),bu t someimprovement shav ebee n"introduce dan dth e
rangeo fexperiment s extended.Th ebiomas s formed wascompose d as indicated
in thesmal lrectangle s inFigur e 1;th enumber s refer to theweigh t ofeac h
fractionpe r 1000gra mo fbiomass .Th earrow srepresen t conversionan d
dissimilation processes,an d thenumber sbesid e them theamount s ofglucos e
andCO ^ involved.0 „wa sno tconsidered ,bu t theamount s involved canb e found
fromdat apublishe d elsewhere (Penningd eVrie se t al., 197 ).Fro mTabl e1
andothe rdat a theamount so fglucos eneede dt osynthesiz e lipids,ligni n and carbohydrateswer ederived .Th e latter fractionwa s assumed toconsis to f
cellulose,whil e theothe r fractions consisto fa natura lmixtur eo fmolecules .
Itwa s alsoassume d thathal fo f the lignini sforme d inmatur e leaves.Th e
amino,acidcompositio n of theprotei nwa s chosent ob e thato f zein (Handbook" ofBiologica lData , 1956).Th ecompositio n of Chetransporte d aminoacids ,
inFigur e 1characterize d asA.A . ,wa sderive d fromsei nb y assumingtha t
theamin oacid s thatca nb e formed fromasparti c andglutami caci d areforme d
from them,an dtha tcystein e istransporte d assuch .Thi s compositionwa s
alsouse d inTabl e2 .Th eothe ramin oacid spresen twer e assumed tob e
synthesized fromglucose ,th eammoni abein gcarrie d inamide s (glutamine and asparagine).Th eresultin g mixture consistso fasparti c acid 41 % (byweight) ,
glutamic acid3 7% ,asparagin e 7% ,glutamin e 15% an d cysteine 0.6 %.
Uptakeo fminerals ,glucos ean damin oacid sar eactiv e processes.O nth e basiso f littlequantitativ e information (Kaback, 1970;Oxender , 1972)i t
isestimate d thatbot huptak eo f 1mol eo fcarbohydrate s and 3mole so fsalt s oramin oacid s requires theenerg y of 1mol eAT Ppe rmembran epassage .
Minerals are takenu p from thexylet nthroug h at leaston emembrane ,an dpas s
twomembrane s of theroo tendodermis .Betwee n thesiev e tubesan d the cytoplasmo fothe rcell sar e atleas t twomembranes ;her e tooth eminima l numberwil lb eused .Energ y foruptak eprocesse s isprovide d byglucose .
Exportcost sar eexpecte d tob e similar toimpor t costs.Bu twhil e sucrose istake nup ,glucos e isexporte d and transferred into sucrose.Loadin g the phloemwit h sucrosei stherefor emor eexpensiv e (eq.4 below )tha nunloading .
Toillustrat e theamoun to freductio nequivalent s andenerg y consumed forNO-^-reduction ,glucos ewa s taken tob e required.Bu ti fNADPH - from chloroplasts isuse d instead,les sglucos e isrequired ,an d less C02 is assimilated and released.Thu s thisnotatio n affects only the internal C0~
turnover rate.Mutati smutandi s thisi s true forothe rprocesse swher e glucose mayno tb e theintermediate .Synthesi so famin oacid s andorgani c acids (OA) isclosel y linkedwit hNO~~reductio n (DeWi te t al., 1963). Theweigh to f
theorgani c acids formed isfoun db y assumingcreatio n of one gramequivalen t oxaloacetic acidpe rgrammolecul eNO .reduced .Som eorgani c acids remaini n
the leavesan d theres tar e transported toth eroot swher e they enter the cellmetabolism .Fo rsimplicit y it isassume d that the carbon skeletons - 8-
yield glucose.Althoug h glucosebreakdow nan d gluconeogenesis dono toccu r inon ecel la tth esam e time,a precis e calculationprobabl y hardly changes thepicture .Th eamoun to fmineral s inth ematur e leaf isrelate d toth e organic acxdcontent .Als o forsimplicit y circulation ofK between leaf androot swa sno tincluded .
Theglucos e required foral lprocesse s results fromphotosyntheti c
CO„-reduction.Th eC O formed duringan ddu e toNO.,-reductio nevolve si n light only,bu t transport andbiosyntheti c processescontinu e indarkness .
Assuming that thesecontinu e indarknes sa t thesam erat e asi n thelight , according toFigur e 1th edar krespiratio n for thewhol e planti s
(353+63+93+22-)53 1gra mCO ,pe r 1000gra men dproduct .Th ene tC O-assimilatio n ratei na nequilibriu m situationmus tb e (2330-1255-531x21 (hours in light)/
24(hour so fbiosynthesis )= 1741gra mCO- .Th e ratioo fne tCO„-assimilatio n todissimilatio n ispredicte d tob e3.7 5 inthi sparticula rexperiment .
Theexperimen twa s repeatedwit h sunflower (Helianthus annuus).Unlik e maize leaves,growin g sunflower leavesus ebot h theirow nassimilate san d thosesupplie db yothe rleaves .Les s transportation costs areincurred ,an d the synthesis ofsom eprotein s doesno trequir eA.A . asintermediates .Th e chemicalcompositio no f thefraction swa sassume d tob e identical tothos eo f maize.Th ecomputation swer eperforme do na simila rbasi s and aredepicte d inFigur e2 .Mainl ybecaus e transportation costsar e smaller,th erat eo f respiration ofwhol eplant s ata give nne t assimilation rate issmalle r than inmaize .
Figures 3a- b show that "steady state"rate s ofassimilatio nan d dissimilation inH .annuu s at2 5 and 18C .The .predicte d ratiobetwee n assimilation anddissimilatio n isgive nb y theslop eo fth esoli d line;it s position ischose nbetwee n theactua lvalues .Th e interceptwit h the z-axis, whichha sa 1: 1relatio nt ox an dy axis,represent s therat eo fmaintenanc e respiration.Ther e isa goo d agreementbetwee n thepositio n ofth emeasure d pointsan d thecompute d slopeove r awid e rangeo f assimilation rates,an d - 9-
therei sn oindicatio n that thelowe rtemperatur e decreases theslope .
Treatmentwit h dilutenutrien t solution decreased thenitroge nconten to f
thebiomas sproduce d to2. 4% .A calculation similar topreviou sone s
showed that this should increase theslop eb y 28 %.Figur e 3cshow stha t
under these conditions thisefficienc y ismaintained ,an d that therat eo f
maintenance respirationwa sno t increased (Semikhatova, 1970).Th emaiz e
experimentswer eperforme d at2 5 ,1 8 and 33C ,an d theresult spresente d
inFigure s 4a-c .Excep t at the lowest light intensities there isa goo d
agreementbetwee n thepositio no f thepoint s andth e calculated slopeo fth e
linea tth ethre etemperatures .I t isconclude d that theseexperiment s confirm
thevalu eo fthi s approach and support thehypothesi s that theefficienc y of
biochemicalprocesse s inhighe rplant s is independent of temperature inth e
rangenormall y encountered. Itwa s suggested earlier (Penningd eVries ,1972 )
thata lo wrelativ ehumidit y could inducesom ewaterstres s in theligh tperiod ,
eliminating the"stead y state"characte ro f theexperiment .T ochec kthi s
theexperimen t at2 5C wa s repeated ata relativ ehumidit y ofabou t 50% .
Theresult sar einclude d inFigur e4 aan ddemonstrat e thatn owaterstres s
developped.McCre e (1970)obtaine d results similar tothos e in theFigure s
3an d4 b yplottin gdail y totals ofdissimilatio nversu s gross assimilation
ofwhit e cloverplants .
Thedashe d lines inth eFigur e4 indicat e theratio s ofne tassimilatio n
ofth ephotosynthesizin g leaves tothei rdissimilation ,whic hwer eno t
measured.Thei rintercept swit h thez-axi sar e foundb ymultiplyin g theplan t
maintenance respiration rateb y thedr yweigh to f thematur e leavesove rth e
totaldr yweight .Th e solid lines inFigure s 3a- b and4 a- c have different
interceptswit h thez-axis ,indicatin g that therat eo fmaintenanc e respiration
dependsupo n temperature,Th e interceptwit h thez-axi si nH .annuu s suggests
thatit smaintenanc e respiration isabou t three times larger than thati n maize,whic h isa nunexpecte d result.Th e rate formaiz e compareswel lwit h - 10-
otherobservation s (McCree, 1970;Pennin g deVries , 1972).
Inmaiz e therat eo f leafappearanc edoe sno t depend onligh t intensity -2 -1 above50-7 0J r n sec (Grobbelaar,1962 ;Gallaghe r and Lof,unpublishe d results).A minima lspecifi c leafweigh t eonsbinedwit h aconstan t rateo flea f production leads toa minima l rate of formationo fbiomass . Iti s -2 -1 suggested thata t light levels'belo w6 0J m sec thisminima l rateo f about0.1 5 gram leavespe rgra mplan tpe r daycoul d notb e supportedb y photosynthesis,bu t issustaine d bybrea k downo fbiomas s and translocation fromolde rorgans ,causin g arelativel y high respiration rate.Thi sproces s continues fora fe wday sa ta diminishin g rate.Figur e 3asuggest s thati n sunflower,unlik emaize ,ther e isn ominima lrat eo f formationo f structural material.Thi swa sals o found in leaveso f lettuce (Bensink, 1971).
Theseexperiment sexclud e thepresenc eo fwastefu l respiration (Beevers,
1970;Tanaka , 1972),excep t one ata lo wan dconstan trate ,whic hwoul d appear similar tomaintenanc e respiration.Th e scattero f themeasurement si nal l experiments isfairl y large,an dma y covera nerro r inth eapproach ,bu tca n alsob e interpreted aschange s of therat eo fbiosynthesis .Researc h onrate s ofbiosynthesi s ofplan tbiomas s and its chemical fractions inrelatio nt o external andinterna l factors isstil l largely terraincognita .A ke y toon e of thefirs tproblem s of thisfield , the.measuremen to f the rateo f biosynthesis ofa nintac tplant ,ma yb e themeasuremen t ofth erat eo f conversionrespiration .
c.Inter2£etation_of_CO ?-assimila^
Steady state conditions areexceptional .Th e rateo fCO„-assimilation " andothe renerg y consumingprocesse s changescontinuously .T ous e aC O- assimilation light response curve (CO^-a.l.c.)correctl y forcalculation s ofplan t assimilateproduction ,externa l conditions (C09-concentration, temperature)an dinterna l conditions (rateo fN O-reductio n and assimilate, export)prevailin g during themeasuremen t anda t themomen t forwhic h the - 11
curvei suse d mustb econsidered . Toasses s therelativ e importance ofC O- assimilation andothe r energy consuming processes somewidel y different exampleswil lb estudied . That theC O-a.I.e .i sno ta constan tbu tsubjec t to stressesan dadaptation s isno timportan t inthi s context,wher eth e maximum rateo fC0 9~assimilation-i smeasure d anduse d asinpu t forfurthe r calculations.
EXAMPLE 1.DURIN GMEASUREMENT SO FTH EC O-A.L.C .TH ELEA FONL Y REDUCESTH E
ASSIMILATED C0„T OGLUCOSE .I nthi s case photosynthesis inC ,plant sma yb e representedb y
6 C0„+ 12NADPH .+ 1 8AT P•* C,Kt„0,. +1 2NAD P+ ISAD P+ 18P . M) 2 2 61 2 ti x v' The energy absorptionpe rassimilate d Cato mi s2 NADPH „ molecules plus3
ATP molecules,expressin g energy absorption inreductio n equivalents andAT P units. Slightly more ATPi suse d inC ^ plants (Maynee tal» , 1971).
EXAMPLE2 .DURIN G MEASUREMENTO FTH EC O-A.L.C .TH ELEA F REDUCESTH E
ASSIMILATED CO TOGLUCOS EAN DFORM S CELLULOSEO RSTARC HO REXPORT S SUCROSE.
Recognizing that glucose-6-P orfructose-6- P isth ephotosynthesi s product, these processes canb echaracterize db y
n glucose-6-P + 2ti ATP -»• starch (2) n glucose-6-P+ 3 nAT P•* •cellulos e (3)
2 glucose-6-P ,,+ 4 AT P• >sucros e (4)
° cell phloem
Synthesis ofcellulos e ismor e expensive than starch synthesis sinceth e monomers mustb eexporte d throughon ecel l membrane.Fo req . (4)i twa s assumed that exporto feac h fructose andglucos e molecule requires 1 ATP molecule,th ecouplin g ofbot h tosucros ea third ,whil e anotherAT Pmolecul e is required foruptak e ofsucros e into thephloem . Assuming that formation of 1NADPH 9 molecule fromNAD P uses7. 5time smor e light energy than 5 ATP molecule fromADP ,i tfollow s that inthes e cases 1.9t o2. 8% mor e energy is absorbedpe rassimilate d Cato m than calculated according toeq . (1). 12
Iti sals oassume d that therati oo fphotosyntheticall yproduce dNADPF Lan d
ATP canvar yaccordin g toth e requirements,a s.suggeste db yRie d (1970).
Photorespirationma yhel p toachiev e this (Tolbert,1971)- .
Thecel lcanno tus eenerg y stored instarc hothe r thani nglucos e
molecules,sinc eit shydrolysi s doesno tyiel dATP .Pro m thepoin to fvie w
ofenerg y conservationstarc han d glucose formation areequal .Th eenerg y
spent toexpor t sucrose (eq.4 )correspond swit h 1.9% o f theenerg yneede d
tosynthesiz eglucose ,bu twit h 5.3 %o f theenerg y stored ini t (perglucos e
molecule3 8AT Pmolecule s canb e formed). Thus5. 6 %mor e glucoseremain s
when theprocesse s described ineq . (4)occu rdurin gphotosynthesis ,a s
comparedwit hglucos e formationi ndayligh t andsucros eexpor t indarkness .
The latterpercentag e represents theundervaluatio n of theyiel d of biosynthesiswhe nphotosynthesi s isconsidere d tob emerel y glucoseformation ,
and isgive n inTabl e3 .
These cases apply toman y laboratory and fieldconditions :ofte nth e
CG„~a.l,c.i smeasure dwhe nNCL-reduccio ndoe sno toccu r and insom efiel d
situations lacko fSO^-reductio n inleave sha sbee nreported .Whe na lea f
forms starchonl yan dexport s sucrosei ndarkness ,th econversio n calculations
described aboveca nb e applieddirectly .
Ifth eC0 ?~a.l.c.i smeasure d incondition s inwhic heq , (1)applie s but sucrose isexported ,th eCO^-a.l.c .ca nb econstructe d froma n initial
slope,equa l toth eslop eo f theorigina l curve divided by theenerg y
absorption ineq . (4)relativ e toeq . (1),an d themaximu m rateo fCO -
diffusion,causin ga maximu mrat eo fenerg yfixation .
EXAMPLE 3.DURIN GMEASUREMEN TO FTH ECG,,-A.L.C .TH ELEA FSTORE STH E C09
ASSIMILATEDA SLIPIDS .Thi s occurs inalga e under conditionswher egrowt h isrestricte d (VanOorschot ,1955 )an dpossibl y inleave so fhighe rplant s whenoi ldroplet s areformed .Whe nth e startingpoin t isphosphoglyceri c acid,(PGA)th eequatio nca nb ederive d 13
31.7mgmo lPG A+2. 5mgmo lNADP H + 146.mgmo lAT P+ 1.0g lipid s + (5)
1.342g C02
Theenerg yconsume dpe rC ato mi nth elipi d fractioni sabou t4 6% mor etha n ineq .(1 )an dunde r thesecondition s theslop eo fth eC0. ?~a.l.c.i scons iderably lowered.Sucros e orglucos ear euse d fortranspor to fcarbo nan d energybetwee ncells ,an dalthoug h slightlymor echemica lenerg ype rgra mC 4 4 ispresen ti nlipid s (4.561 0 Joule)tha ni nstarc h (3.361 0 Joule),i nth e conversiono flipid s into glucose some2 8% o fthe .G get s lost.Thi s reduces theyiel do flipid sconsiderably :
1.47g C0 2• +0.5 2g lipid s~ >0.7 2g glucos e (6)
1.47g C0 „- •0.9 0g starc h•+ •1.0 0g glucos e (7)
Storageo flipid sma yb eadvantageou swhe n lowweigh t isimportant ,a s insom eseeds ,o rwhe n thespecifi c characteristicsar euseful .Th ehig h costso fglucos esynthesi s from lipidsma yb eth emajo rreaso ntha t lipids areno tuse dfo rshor t termstorag ei nleaves .
EXAMPLE k-.DURIN GTH EMEASUREMEN TO FTH ECO^-A.L.C .TH ELEA FREDUCE SNO j
ANDFORM SAMIN OACIDS ;C O ISREDUCE DONL YT OPROVID ECARBO N SKELETONSFO R
THEACIDS .N0~-reduction ,amin oaci dan dorgani caci d formationca nb e describedb y
1.785g glucos e+ 0.53 5g NQ ~-» -1.0 0g amin oacid s+ 0.56 7g (8)
organicacid s+ 0.44 7g C0 „ andb y
+ 49.3mgmo lCO ?+ 119.mgmo lNAPPH 2 181.mgmo lAT P+8.6 2 mgmolNO ^
-*-1.0 0g amin oacid s+ 0.56 7g organi c acids (9)
Inth eprocesse s describedb yeq .(9) ,23. 0% mor e energy isconsume dpe r assimilated Cato mtha n ineq .(1) .I fi twer esuppose d thatonl y glucosewa s formedphotosyntheticall yan damin oaci d synthesis occurred indarkness ,th e conversioncalculation swoul d underestimate theyiel d ofth ephotosynthesi s - 14-
processb y !9.8% ,an d9 Zo fth eassimilate d CO remainsunreduce d and isexported ,i norgani c acids toth eroot san dexcreted .
Likestarc h formation duringphotosynthesis ,storag eo famin oacid s asprotein s increases theenerg y fixationpe rassimilate d Cato m(t o24. 1% ) but thisi slos tdurin gprotei nhydrolysis .Expor to fth eamin oacid si s relatively cheapan dwhe ni toccur s during photosynthesis theenerg yassimilati o perC ato mi sincrease d only to21. 3% .
EXAMPLE 5.DURIN GTH EMEASUREMEN TO FTH ECO^A.LX . THELEA F INCREASES
INBIOMASS ,BU TDOE SNO TEXPOR TO R IMPORTASSIMILATES .I nthi sexampl e photosynthesis canb edescribe db y
38.2mgmo lCO ,+ 96. 5mgmo lNADPH. .+ 145.mgmo lAT P +0.09 2g mineral s
+0.15 7g N0 ~ -*•L.0 0g plan tbiomas s (10)
Eq.(10 )va sobtaine db ymodifyin g Figure2 suc h tnatal l growthoccurre d inth ephotosynthesizin g part,an di ti sconclude d that theenerg y absorption perC ato mi s26. 7% mor e than thatcalculate d fromeq .(1) .Thi s resultdepend s onth echemica l compositiono fth ebiomass ,whic h inthi sexampl e isver y richi nminerals .Fo rbiosynthesi s fromglucos ei ndarknes s theequatio ni s
1.49g glucos e+ 0.15 0g 0 2+ 0.15 7g N0 ~+ 0.09 2g mineral s
+ 1.00g plan tbiomas s+ 0.50 2g C0 2 (11)
Performing theprocesse s describedb yeq .(10 )durin gphotosynthesi syield s
30% mor edr ymatte r thanperformin g thoseo feq .(!) ,wit h thoseo feq .(11 ) * occurringi ndarknes sI
Leaveso fbea nan dsunflowe r plants gothroug h thisstage ,bu tgenerall y mosto fth egrowt hoccur si ndarknes s ori norgan s thatd ono tphoto - synthesize.Fo rleave sgrowin gfro mthei row nassimilate s theefficienc y ofC utilization ,expresse d asth epercentag eo fassimilate dC O-molecule s retained inth eplan t2 4hour safte r application,mus tb ebetwee n 100 %
(eq. 10)an d7 0 Z(eq .1 1plu seq .1) .Whe n leavessen d their assimilatest o matureorgans ,suc ha slowe r leaves toroots ,thes e assimilates areuse d for- 15
maintenance exclusively,an d thus theC utilizatio n is0 % ,althoug hsom e
labelledC ma yb eretaine d duet oexchang e inturnove rprocesses .I tca n foeestimate d thatsom e7 0% o f theassimilate d Ci sretaine d in theplan t
permanently atrelativ e growthrate so f0, 3 g.g .day andhigher ,abou t
50% a ta relativ egrowt hrat ao f0.03 ,an d about 30% a ta relativ egrowt h
rateo f0.01 .Estimatin g thefraction s ofsubstrat e consumed formaintenanc e
andbiosynthesi s gives theke y forthes epredictions .
Acknowledgeioent s
The authori sindebte d toDr.Ir .C.T .d eWi t forreadin g themanuscrip t
critically and toMis sH.H .va nLaa ran dMr .W .va nde rZweerd e forcarryin g
out theexperiments .Th e chemicalanalyse swer edon eb y theIB Schemica l
laboratory. 16-
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requirements andefficienc y ofbiosynthesis ,a quantitativ e approach.
InPrep . - iy -
Table 1.Value scharacterizin gconversio no fglucos e into themai n chemical fractionso fplan tdr ymatte ri ndarkness .Eac h fractionconsist so fa natura lmixtur eo fdifferen tmolecules ,
yield oxygen carbondioxid e consumed produced chemical fraction note gproduc t g o2 gco2 gglucos e gglucos e gglucos e
nitrogenous compounds 0.616 0.137 0.256 + NH3 (consistingo famin oacids , 0.404 0.174 N0- proteinsan dnuclei cacids ) 0.673 + carbohydrates 0.826 0.082 0.102 lipids 0.330 0.116 0.530 lignin 0.465 0.116 0.292 organicacid s 1.104 0.298 -0.050
Table2 .Requirement sfo rbiosynthesi so f 1.00gra mdr ymatte ro ftissue s withdifferen t chemicalcompositions .Th ecompositio n usedi sgive n inpercen to fnitrogenou s compounds,carbohydrates ,lipids ,ligni n andmineral srespectively .
amino co2 02 natureo fbiomas s composition sucrose acids produced consumed (gram) (gram) (gram) (gram) leaves 25;66.5;2.5;4;2 1.055 0.305 0.333 0.150 nonwood yste m 12.5;74;2.5;8;2 1.153 0.153 0.278 0.135 woodyste m 5;45;5;40;5 1.515 0.061 0.426 0.176 beanseed s 35;55;5;2;3 1.011 0.427 0.420 0.170 riceseed s 5;90;2;1;2 1.135 0.061 0.186 0.110 peanutseed s 20;21;50;6;3 1.915 0.245 1.017 0.266 bacteria 60;25;5;2;8 0.804 0.732 0.573 0.208
Table3 .Th ehydroge nan denerg yrequirement s duringphotosynthesis , theadditiona lenerg y assimilationan dth eyiel d undervaluation indifferen texample sexplaine di nth etext . requirementspe r additional undervaluation calculated assimilatedC0 „molecul e energy drymatte ryiel d from assimilation equation NADPH2 ATP
example1 2.00 3.00 0% 0% - example2 2.00 3.33 2% 0 % 2 example2 2.00 3.33 2% 6% 4 example3 2.74 5.65 46% -28% 5.6+7 example4 2.47 3.73 21% 20% 9.8 example5 2.53 3.80 27% 30% 10,10+11 , ...... _ . ... - 20-
Legendo ffigure s
Fig. 1. Aschemati crepresentatio no fassimilatio no fcarbo nan dnitroge n
end theirutilizatio n intaai.s eplants .Th e rectangles indicateen d
products,th ecircle sintermediates .Doubl e lines indicate
'processesoccurrin g duringphotosynthesi s only,singl e lines
conversionso r translocations*an ddashe d linesC0_-foraation .
. Thenumber sgiv e thecorrespondin gweights .
Fig.2 . Aschemati c representation ofassimilatio n of carbonan dnitroge n
and theirutilisatio n insunflowe rplants .Hal fo f thedr ymatte r
increaseoccur si nphotosynthezin g leaves.Fo rexplanatio nse e
fig.I .
Fig. 3a. Therelatio nbetwee nassimilatio nan ddissimilatio n ina "stead y is IP f\ state"situatio n invho' esunflowe r plants at2 5C .
3b. Therelatio nbetwee nassimilatio n anddissimilatio n ina "stead y
state"situatio n inwhol e sunflowerplant sa t 18C .
3c» Therelatio nbetwee n assimilation anddissimilatio n ina "stead y
state"situatio ni nwhol e sunflowerplant s at2 5C .Plant swer e
grownan dmeasure d ata dilute dnutrien t solution.
Fig.4a . Therelatio nbetwee nassimilatio n anddissimilatio n ina "stead y
state"situatio n inwhol emaiz eplant s at 25C,an da t 85%
(crosses)an d5 0 %(dots )relativ ehumidity .
4b. The relationbetwee n assimilation anddissimilatio n ina "stead y
state"situatio n inwhol emaiss eplant s at 18C . - 21~
Fig* 4c. Therelatio nbetwee nassiailatio n anddissimilatio ni na "stead y
state"situatio n inwhole-maiz eplant s at3 3C .
Desired sizeso ffigures * includinglegends :
figure 1 halfpage .
" 2 halfpag e
" 3a+3b*3c halfpag e
" 4a-«-4b-s-4c halfpag e »*. Cttf—-I ID ^ «•* CO IOCO O »- 1 .. /
z X UJ UJ O _l X 0.
0> p «* p,- IDU1 00 r*
C7I c
01 JZ
o x: a.
Figure 3a
40 NETASSIMILATIO NVERSU SDISSIMILATIO N INSUNFLOWE RPLANT SA T 25° C net assimilation mg C02/g dry matter/hour
30
20
10 -
Helianthus annuus 25°C
10 15 mg C02/g dry matter/hour dissimilation
-5 z-axis Figur e3 b
40 NETASSIMILATIO NVERSU SDISSIMILATIO N INSUNFLOWE RPLANT SA T 18° C net assimilation mg C02/g dry matter/hour
Helianthus annuus 18°C
10 15 mg C02/g dry matter/hour dissimilation FIGURE3 C NETASSIMILATIO N VERSUSDISSIMILATIO N INSUNFLOWE RPLANT SA T 25° C (DILUTEDNUTRIEN T SOLUTION) 40 net assimilation mg COz/g dry matter/hour
Helianthus annuus, 25°Cfdiluted nutrient solution
J 10 15 mg C02/g dry matter/hour dissimilation
z-axis FIGURE4 A NETASSIMILATIO NVERSU SDISSIMILATIO N INMAIZ EPLANT SA T 25° C
40 net assimilation mg C02/g dry matter/hour
Zea mays , 25° C
10 15 mg COz/g dry matter/hour dissimilation
z-axis FIGURE4 B NETASSIMILATIO NVERSU SDISSIMILATIO N INMAIZ EPLANT SA T 18° C 40 net assimilation ,* mg C02/g dry matter/ hour
30
20 -
10 -
Zea mays /18°C
10 15 mg C02/g dry matter/hour dissimilation
-5 z-axis FIGURE*4 C NETASSIMILATIO NVERSU SDISSIMILATIO N INMAIZ EPLANT SA T3 3° C
40 net assimilation mg C02/g dry matter/
Zea mays,33°C
10 15 mg C02/g dry matter/hour dissimilation
z-axis THECOS TO FMAINTENANC EPROCESSE SI NPLAN TCELL S
F.W.T.Pennin gd eVrie s
Department ofTheoretica lProductio nEcolog y
AgriculturalUniversity ,Wageninge n
TheNetherland s
Accepted forpublicatio n inth eAnnal so fBotan y THECOS TO FMAINTENANC EPROCESSE S INPLANT 'CELL S
F.W.T,Pennin g deVrie s Department ofTheoretica lProductio nEcolog y AgriculturalUniversity ,Wageninge n
AJ5£mACT
Themos t importantmaintenanc eprocesse s inplan tcell s areprotei n turnover andactive? ,transpor tprocesse s tomaintai ncertai n ion concentrations inth ecells .I n thispape ra nattemp t ismad et ocalculat e thetota lenerg y costo f theseprocesse s fromwha t isknow n about theirspecifi c costs andwha t hasbee nobserve d about theirrates .Mainl y because of lacko fsufficien tan d reliabledat aabou trate s ofindividua lmaintenanc e processes,onl y approximate valuesca nb eobtaine d asyet .
Theaverag e turnoverrat eo f leafprotein s mayb eabou t J00m gprotei n per gprotein spe rda y atnorma l temperature inleave sassimilatin g atmoderat e lightintensities .Thi sproces s consumes 28-53m gglucos epe r gprotei npe r day,whic hequal s 7-13m g glucosepe rg dr yweigh tpe rda y inleaves .I ti s likely that theprotei n turnover ratean dcel lmetaboli cactivit y arerelated .
The costo fmaintainin g ionconcentration s isestimate d tob eabou t6-1 0rag glucosepe rg dr yweigh tpe rda y inleaves .Thi svalu e isals oa napproximato r mainlybecaus e theintercellula r ionconcentration s areunknown .Th esu mo fth e figures is lowertha nwhat,inaccurate,measurement so fmaintenanc e respiration ratesindicate .On ereaso n for theunderestimatio nma yb e that theprotei n turnoverrate suse d inth ecalculation s apply toplant s thatwer e less itietabolicallyactiv e than theplant so fwhic h themaintenanc e respirationwa s measured.
Effects ofwate rstres s and salinity,temperatur e andothe r environmental factorso n the rateo fmaintenanc eprocesse sar ediscussed ,bu t at thepresen t stageo fphysiolog y only afe wobservation s ofchange dmaintenanc e respiration ratesca nb e fullyexplained .
Theconsumptio no fassimilate s formaintenanc eo fplan tcell s isa significant,negativ e factorfo rplan tproductivity ,A bette runderstandin g ofmaintenanc erespiratio nprocesse sma y givea clu e tomanipulatin gplan t environmentan dplant ,characteristic s forreducin g theamoun to f assimilates consumed Inthes eprocesses .I t issuggeste d that anartificia l reductioni n proteinturnove rrate sma yb eon eo fsuc hmanipulations ,whil epossibl y also the.cos to fmaintainin gio nconcentration s canb e lowered.However ,a considerablenumbe ro fwel ldirecte d studies about rateso fmaintenanc e processeswil lhav e to becarrie d outfirst .
INTRODUCTION
All livingcell sexpen d energy formaintenanc epurposes .A fe wattempt s havebee nmad e toestablis h experimentally theenerg y involved inplant san d it.wa s found that thisca nb e anappreciabl e amount,I ns o fara sth eautho r isawar en ostud yha sbee npublishe d oncalculatin g theMaintenanc e costo f planecell s frombasi cdata .Thi spape rpresent s anintroductor y calculation of theenerg y andsubstrat e requirement for themaintenanc eo fcell so fhighe r plants,whic h islargel ybase do ninformatio nfro mth eliteratur e ennatur e andrat eo funderlyin gprocesses .Th epresen tknowledg eonl y allows tomak e a firstestimat e ofmaintenanc ecost ,bu tdoe salread y indicatemai narea s forfurthe rresearch .
The term"maintenance "include s theprocesse s formaintainin g cellular structures and gradients ofion s andmetabolites ,an dphysiologica l adaptation processes thatmaintai n thecel la sa nactiv euni ti na changin genvironment .
Formation ofne wenzyme s atth eexpens eo fother san d saltaccumulatio n in sora-2stres scondition s areexample so fsuc hadaptations .Hence ,maintenanc e isno t aproces s asconservativ e asit snam esuggests .Whe nusin g theconcept s
"maintenance"an d "growth"i tha s tob e realized that these terrasalway s concerna certai n levelo fcomplexity : anecologis tma y consider growtho f - 3-
anorganis ma son eof :th eprocesse smaintainin gch epopulatio n size,whil e maintenanceo fch enumbe ro ferytrocyte s isa growt hproces s toth ehistoiogis t
Thisstud yconcentrate so nmaintenanc eo fcells .Soa eredistributio n processes
inplant sca nb e regardeda smaintenanc eprocesse s ofth eorganism ,bu tthes e
areno tstudie d inthi spaper ."Maintenanc erespiration "refer s toth eCO. ,
that results fvossprotei nbreakdown ,plu sth eC0 2 produced inrespirator y processes thatprovid e energy for themaintenanc eprocesses .
Incalculatin gth emaintenanc ecos t informationi sneede d about therate s cfprocesses ,thei rspecifi ccost san d theefficienc y ofenerg yproduction .
De**ivati-->no frate so f individual.maintenanc eprocesse s frommor ebasi cdat a
in ic-tilf' H&yet ,sinc e little isknow no f theirmechanism s andregulations .
Thus,observation so fsuc hrate sar e indispensable.Mainl y because theirnumbe i issr.il iver y limited only somegenera l conclusionsca nb edraw nwit h respect
totrv imagnitud eo f thecos tof :maintenanc eprocesse s inplan tcells .T ofin d
citespecifi ccost ,o fmaintenanc e processes,th e costo fmaintainin g concentrationso fion san dmetabolites , thebiochemica l costo fbreakdow nan d
resynthesiso ftaclecule san d theus e tob emad eo f.breakdow nproduct swil l beconsidered .Beaver s (1961)collected ,evidenc e thati nplant s undernorma l conditions theefficienc y ofenerg y utilization fromorgani csubstrates , measured asth eP: 0rati oo fKADH. .oxidation ,i sclos e toth emaximu mvalu e of 3,a si nanimal s (Lehninger, 1970). LowerP: 0ratio shav eofte nbee n observed,bu tma yb eattributed ,a tleas tpartly ,t oth eprocedur eb ywhic h mitochondriawer eisolate d (Roinanian dOzelkok , 1973). Inth e calculations itwil ltherefor eb eassume d thatmitochondria lphosphorylatio n (inno n stressed conditions)i smaximall y efficient;fo rbacteri ather ei sevidenc e thatth eP: 0rati oma yb econsiderabl y lesstha n3 (c fStouthainer ,1973 ;
Stouthameran dBettenhausen , 1973).Th e substratedeman d formaintenanc e processes increases inverselywit h thisefficiency .Sinc eglucos eo rothe r oligo-saccharidesar econsume d firstfo renerg yproduction ,maintenanc e cost willb eexpresse di nm g glucosepe rg dr ymatte rpe rday .Becaus e the.rati o - 4-
ofmole sC0 ? produced tomole s0 „consume d inmatur eorgan sunde rnorma l conditionsi smostl y aboutunit y (James,i953 ) complete oxidationo fglucos e willb eassumed .
RATESAN DCOS TO FMAISTENANC EPROCESSE SUNDE R STANDARDCONDITION S
Maintenance_of_molt|Cular_structures
§E§.§lt42wn_and_re£yntJi^ Onlya shor taccoun t of thspresen tstat eo fresearc ho nprotei n turnoverwil lb egiven ,fo rdetail s the.reade ri sreferre d toreview sb yGlaszio u <1969) ,Schirak e (1969),Schimk e andDoyl e (1970),Pin e 0972)an dSiekevit z(1972) .I nspit eo fmuc hresearc h inthi s field iti sstil ldifficul t toconstruc tmor e thana genera lpictur e ofprotei n turnover indifferen torganism sari di nplan torgan sparticularly .
Mostlyprotei nbreakdown ,i sa nenzymati cproces s (Travis,Huffake ran d
Key, 1969;Pine ,1972) ,bu tn oenerg y seemsrequire d forpeptid ebon dcleavag e
(Pine, !972).Onc edegradatio n startsenzym eactivit y decreases exponentially.
Schirake (1969)an dPin e (1972)suggeste d that,a sa genera lrule ,enzymes'ma y beautomaticall y stabilized againstproteolysi swhe ninteractin gwit h their substrates.Bot henzym esynthesi san dbreakdow nca nb eregulate d (Schirakean d
Doyle, 1970;Trewavas , 1972),bu tth econtro lmechanis m ineukaryote s isstil l largelyunexplained .Lon g termchange s ofenzym eactivit y indicatemostl y breakdowno rd enov osynthesi s (Beevers andHageman , 1969;Travi se tal. ,1969 ;
Zucker, 1972;Oak se tal. ,1972) .
Informationcollecte db yPin e (1972)indicate s thatth ebul ko fbacteria l protein (70% )i sstable .A smal l fraction (1-7% )ha sa turnove rrat econstan t
(abbreviated toturnove rrate )o f 17.- 70.g protei npe r g proteinpe rda y
(abbreviated to 17.- 70 .da y ;i trepresent s the relativerat eo f decreasewhe nexponentia ldeca y occurs). Theothe rprotein s arestabl ei n growingbacteria ,bu thav ea turnove r rateo fabou t2. Ada y inno ngrowin g conditionswha nthes eresul t fromnitroge nstarvation .Overal lprotei n turnover -5 -
amounts to0. 6- 0. 7da y v ingrowing s *nd to1. 2- 1. 4da y inno ngrowin g bacteria.
Theliteratur eabou tplan tprotei n turnover islimite d andconcern sraainly leaves.Turnove r rateso ftota llea fprotei nwer ereporte d tob eabou t0.3 0 day intobacc oleave s (Holasenan dKoch , 1964),measure da sth erat eo f 14 incorporationo f CO,,int oproteins .Sinc eprotei n turnoveri spossibl e without incorporationo f Cl>2int oamin oacid s thiswetho dprovide sa minimu m value.O nth eothe rhand , C09 isusuall y supplied ata hig h concentration inhig h light,an da resultin ghig hassimilatio n ratema ystimulat eenzym e synthesis.Racuse nan dFoov e (1962)determine da rat eo f losso flabelle d protein-serins atiiprotei:i--glycin oo fbea nlea fdisc san dfoun d about0.?.? . day .Hellebus tan dBioi/el l(1964b )reporte dprotei n turnover rateso f
0.11da y inrapidl y growingwhea t leavesan d0.0 4da y inexpandin g tobacco leaves,whil e thato fno ngrowin gwhea t leaveswa s0.0 6da y ",an d ilmostzer o inno ngrowin g tobacco leaves.The ymeasure dthe . ratao flos so f '^CO.fro m previously labelledprotein? ,whic h infac treflect samin oaci d turnover rathertha nprotei nturnover .Th edecreas e inturnove rrat ewa sascribe dt o celldifferentiatio nbein gfinished .Th erat eo fprotei nbreakdow n ingrowin g
Leraaamino r undernonaa lcondition s is0.09 6+ 0,00 5da y (Trewavas, 1572).
Protein turnoveri nChlorell awa sfoun d no bea slo wa s0.0 1- 0.0 2da y
(John,Thurstonan dSyrett , 1970).I nthes estudie s relatively rapid labelling or losso flabe lo fa smal lriactio nwa sno tobserved ,suggestin g thateithe r a fractionwit ha hig h turnover ratewa sv^r ysraal lo rabsent ,o rtha ti t hada separat e aminoaci dpool .Th epreviousl y Labelledsolubl eprotei n fractionminu s ribulose 1,5diphosphat e carboxydismutase (RuDPCase)c fbarle y leavesco-.'tprise sabou thal fo fth etota l leafprotein san dsl-ovc- da los so f 14-1 —'
C0„o f0.1 4da y ata constan t light ioUfir:.-;X'".yo fabou t 30 V n '"
(Peterson,Kleinkop fan dTiuffaker , 197'!).Suc hprotei n turnoverrate si«.!.lo w adaptationo fth eenzym e system capacity toenvironmenta lchange s in2 t o4 days,whic hi s thecsrvee te>: More Informationabcu tprotei nturnove rca nb efoun d on theleve lo f individualenzyases .However ,seldo mquantitie s ofenayma sar ereported ,whic h isa grea thandica pi nusin gthes edata .Som eenzym e turnoverrate shav e beencollecte d inTabl e 1.Th ehig h rateo fvacuola rinvertas e insuga rcan e wasquestione db yTrewava s (1972)o nth ebasi so f themetho d used.Degradatio n audresynthesi s ofRuDPCas ei nexpande dbarle y leaveswa s investigatedb y ... i ?et*r30ne tai . (1973). Indarknes s therat eo fdegradatio nwa sabou t0.0 6 day' initially,increasin g to0.3 8 day after3 0hrs ,an d th«adecreasing .Whe n theplant swer e returned toth eligh tRuDPCas ewa sreayntheaiae d ata rat eo f 0.12day " initially ando f0.5 5 day after2 0hrs .Degradatio n ofRuEFCaa e inconstan t lighty« sno tobserve d and itsturnove rwithi n thechloroplast s is unlikely.Turnove ro fRuDPCas e isparticularl y important,sinc ei t constitute-,-.;30-7 0% o£ the total leafsolubl eproteins . Asii ibacteri aan dy* :asrs(Handelstam , I960),DN Aturnove ri nful lgrow n leavesi sver yslo w (Dyeran d Osborne, 1971).Becaus eo E thesmal lamoun t involved inplant s (0.5- 1.5% o fth eweigh t of the nitrogenous compounds) and thelo wcos to fresynthesi s frommonomers ,ONA .maintenanc ewil lb e neglected. Therat eo fmRN A turnover seemsrelate d coth erat- io fprotei nsynthesi s (Korrisan dKoch ,1972 ;Rot han dDampier , 1972)anc ?i cmuc hmor e intensive thantha to ftRN Aan drRN Ai ngrowin gbacteri a (Norrisan dKoch , 1972)an di n growingLemn amino r (Tabic i).Cos to fRN Aturnove r ingrowin gcell s issmal l compared toth ecos to famin oaci dpolymerizatio n (e.g.Stouthamer , 1973). Maintenance ofRN Aan denzyme s forbissyntheti cprocessu swa sestimate dt o consume theenerg y ofabou t !AT Pmolecul epe rpeptid ebon d (Penningd eVrie.s , Brunstingan dVa nLaar , 1974).I nanalogy.i t isasswue dtha tth ecos to f maintainingprotease s and theirmRN Ad ono texcee d 1AT Pmolecul ep^ rpeptid e bondo fr.h edegrade dproteins .Polymerisatio ncoa t is 3o r4 AT P moleculespe r peptidebon d (Lucas-Lenard and Lipts-ani::.,1971) , HO r.hacth e lowest:turnove r table 1.Som eenzym ean dRN Aturnove rrate si nvariou splan t tissues undernorma lconditions . enzymean dtissu e turnoverrat e reference (day""1) NO--reductase,maiz eseedling s 3.6 Glasziou,196 9 NO--reductase,maiz eroots ,degradatio n ratei na N0_-fre emediu m 4.1 Oakse tal. , 1972 hexoseuptak esystem ,Chiore11 asp . 4.1 Tannere tal. ,197 0 phenylalanineammoni alyase , mustard seedlings,degradatio nrat e indarknes s 2.9 Glasziou,196 9 isocitrate lyase,Chlorell asp. , degradationrat ei ndarknes s 2.2 Johne tal. ,197 0 invertase,suga rcan e 4.8 Glasziou,196 9 invertase,artichok ean dcarro t 1.5 Trewavas,197 2 invertase,suga rbee tan dre dbee t 0.7 Trewavas,197 2 cellulase,pe aepicoty l 0.6 Glasziou,196 9 • RuDPCase,expande dbarle yleaves , degradationrat ei ndarknes s 0.06-0.38 Petersone tal. ,197 3 synthesisrat ei nligh t 0.12-0.55 Petersone tal. ,197 3 isocitratelyase ,melo n 0.36 Glasziou,196 9 malatesynthetase ,melo n 0.36 it RNA-ase 0. tt peroxidase 0. it N0~-reductasemRNA ,maiz eroot s 48. Oakse tal. ,197 2 mRNA,potat otube r 7. Glasziou,196 9 peroxidase,mRNA,suga rcan e 7. ii cytoplasmarRNA ,Lemn amino r 0.17 Trewavas,197 0 chloroplastrRNA ,Lemn amino r 0.05 ti - 7- costpe ramin oaci d isabou t 5o r6 AI Pmolecule spe rbond ,an d this corresponds to0.2 2 -0.2 6 gglucos epe rg protein . Someamin oacids ,however ,ar eno trecycle dbu tcombuste d andne wamin o 14 acidsar e formed.Thi sproces scause s C00 release frompreviousl y labelled 4m. proteins.Synthesi so f 1.g o fprotein s requires 1.655g glucos eplu sNH. , whileit sdegradatio nyield sNH ~plu sa smuc henerg y as 1.22 gglucos edoes , wheni ti scompletel y oxidized.I nthi scas eprotei nan damin o turnover require 0.43 gglucos epe rg protein . Thelatte rvalu eshoul db euse dwhe nlos s 14 . of C0„ fromlabelle dprotei n xsdetermined ,an d onebetwee n these twovalue s iflos so fenzym e activity ismeasured .Th emagnitud e of the fraction recycled and thatcombuste d isalmos tunknow n (Hellebust and Bidwell, 1964a;Trevavas , 1972).Fro mth edifferen t turnoverrate so fvariou s amino acids inTrewava s experimentsi tma yb e inferred that animportan t fractionwa srecycle d intha t particular .vase;Lehninge r (1970)mention s that inma n over7 5 %o f theamin oacid sar erecycled .N oothe rindication s about this important parameterwer efound . Ina detaile d description ofman y experiments Shlyk (1970)reporte da n averagerat eo fabou t0.1 0 day forbreakdow n and denov osynthesi so f chlorophylli ngrowin gan dmatur eleave so fhighe rplants .Fro m thebiochemica l pathways leadingt ochlorophyl li tca nb e calculated that synthesiso f 1.g chlorophyll requires2.2 9 gglucos eplu s someNH -an d Mg,whil eit sbreakdow n yieldsabou t i.5g glucos epe r gchlorophyll .Leave scontai nonl y 15-35m g chlorophyll perg nitrogenou s compounds,an d itfollow s from thesefigure s thatcos to fchlorophyl l turnover ismuc hsmalle r than thatc f leafproteins . Tocalculat e thetota lcos to fmaintenanc e ofth e leafnitrogenou scompound s roughlysom eassumption sar emade .Lexande re tai . (1970)foun d that the non-proteinnitroge n fractioni nth e leaveso f 22specie swa s about iO% o f thetotal ,nitroge n fraction,wit honl y twoexceptions :Helianthu sannu-j s (2.5 %)an dBrassic anapu s (31 %). It isassume d therefore that 107 .o fth e leafnitrogenou scompound s arestable .Furthermor e iti sassume d that4 4 Z - 8- ofth e leaforgani cnitroge ni si nRuDPCase ,an d that thisenzym e isdegrade d for 10hour spe rda ya ta rat eo f0.14 4da y ,tha tth eresultin gamin oacid s arestore d inprotei nan d that theenzym ei sresynthesiza d for6 hour spe r day ata rat eo f0.2 4 day .Thre epercen to f theorgani cnitroge n issuppose d tob ei nchlorophyll ,an d theres ti nprotein swit h aconstan t turnoverrat e of0.1 5 day .Fro m theserate si t follows that themaintenanc ecos to f nitrogenouscompound s isbetwee n2 8an d5 3m gglucos epe rgra mpe rday . Because therat eo fprotei n synthesis isno tconstant ,ha sha sbee n demonstrated inviv ob yStee r (1973), thecos to fprotei nturnove r showsa diurnalpattern .A relativel y large fractiono fthes e costs arerequire d in thefirs thour safte r theonse to f light.-I ti sthu s likely that inductiono f enzymesynthesi sa ta sudde nonse to f lightcause sa burs t inenerg y requirements,and .thu si nrespiration .Heiche l (1970)reporte d astimulatio n of maize leafrespiratio n for2- 3hour s followinga nilluminatio no f2 0minute s inCO. ,fre eair .Thes eexperiment swer erepeate db y theautho rwit hmatur e leaveso fLoliu mperenne ,Phaseoiu svulgaris ,Ze amay s andHelianthu sannuus , —2 growni nhig h lightconditions .A n illuminationperio do f6 0minute s (300W m ) wasused ,precede db ya perio d ofdarknes s of I- 2 4hours ,an di na n atmosphereo f30 0pp mC0 2. The"pos tilluminatio nburst" ,fro mwhic hi s subtracted thecos to f translocation ofth eassimilate s formed (Penningd e Vries, 1974),wa ssmal lafte r 1an d 3hour s darkness,an dabou t twicea slarg e astha tobserve db yHeiche lafte r6-2 4 hours,excep t inLoliu mwher e stimulationremaine dsmall .Heiche l found that theC0 „produce d inthi s"pos t illuminationburst "depend so nth eirradiance .I tcorrespond swit h theamoun t ofC O formed,whe n 1- 4 % o f the leafprotein s are.broke ndow nan dother s resynthesized. Zucker (1972) reported thatafte r induction5 - 70% o fth e proteins synthesizedma yb ea singl especies ,th eamoun to fwhic hma ywel l exceed 1% o fth etota lprotei n (Mandelstam,1960 ;Tanner ,Grime s andRandier , 1970).Amin oacid s forthes eenzyme sma ycom e fromchymotrypsi ninhibito r 1, which servesa sa reserv eprotei n (Ryanan dHuisman , 1970).I t issuggeste d - 9- thatth ephysiologica lphenomeno no f"pos tilluminatio n respiration"an d the biochemicalphenomeno no fenzym einductio nar edifferen t aspectso f thesam e process. §£SBM2HS_S2^_I'§S25S^2SiS-2f„Ii£i^£iBielesk i (1972)observe d that Prelease d fromphospholipid s ingrowin gSpirodela . was lesstha n0. 2 day .Kawag ae tal . 14 (1973)measure ddisappearanc eo f C frommembrane si ngerminatin gcasto r beanendosperm ,an dobserve d rates ofoveral lmembran e turnovero f0. 4- 1.7 day ,an do f4. 8da y *o f apar to f the"ligh tmembran e fraction".Lecithin e moleculesan deve n largermetnbran efraction swer epossibl y recycled. Innon - growinganicia lcell smembrane s turnedove ra ta rat eo f0. 5 - 1.2da y (Pine, 1972).Estimatin g that 4% o fth edr yweigh tconsist so fmembrane s (fromestimate so f totalmembran esurface ,it sthicknes san ddensity) ,an d assumingarbitraril y thaton e tentho fit sprotein s and lipids arecompletel y degradedan dresynthesiae dfro mglucos ean d that theres ti srecycled ,th e costo fmembran emaintenanc ei s1. rag7 glucos epe r gdr ymatte rpe rday . Breakdown andresvnthesis_of__other_cell__co^onents .Bacteria l cellwal l componentswer e found tohav ea turnove rrat eo f0. 3 - 1.0pe rgeneratio n time(Mauc kan dGlaser , 1970),bu tcel lwall so fhighe rplant s arestable . Holmsenan dKoc h (1964)foun dn olabellin go fpolysaccharide s after adding labelled glutamatet oth eleaves .Auxi nwa sshow n tob erapidl y degraded withinth ecel l(34 .da y ,DelaFuent e andLeopold , 1970),bu t thisconcern s anextremel y smallamount .Cel lorganell s areno t turned over asunits ,excep t forver ysmal lorganall s (Pine, 1972). Useo fturnover .Th eus eo f turnoverprocesse s inplant sma yb eshortl y discussed herebecaus eo fit simportan t implications forplan tproductivity . Siekevitz(1972 )speculate d aboutprotei ndenaturatio nb yheav ynetals , incorrectly constructed - 10- proteins andoptimalizatio no fRN Aan dDN Aus ea spossibl e reasons leading too rjustifyin gprotei n turnover."\Mandelstam'ssuggestio n (I960),however , ^ thatprotei nbreakdow nan dsynthesi smainl yprovide s amean s offormatio no f otherenzyme swhe nne tcel lgrowt h isstoppe d isno wwidel y accepted for bacteriaan danimal s (Lehninger, 1970;Pine , 1972),an dexplain s themod eo f adjustmento f thebiochemica lmachiner y toenvironmenta lchange san dpossibl y anticipation thereof.Onl y rapidan dconstan t turnovero fsom eprotein si n growingbacteri ai sno texplaine db y thishypothesis .Adaptatio n toa change d temperature canoccu rb y formation of (iso-)enzymesi nmatur e ceils.Suc ha processha sbee nobserve d for theenzy mNADP-isocitrat edehydrogenas ei n rainbow trouts (Moonan dHochachka , 1971)an di sa for mo fadaptatio n forwhic h breakdownan dsynthesi so fprotein s arerequired .Adaptatio n supports competitionvigo ran d thus survival,bu t itsburde n iscos t ofprotei nturnover . Plant cells function ina variabl ephysica lenvironment ,bu t their chemical environment ismuc hmor establ e thantha to fbacteria .Th etim eneede d foradaptatio no fenzym eactivit y inlea fcell s toa change d levelo fligh t intensity ortemperatur e isconsiderabl y largertha nth etim eneede db y bacteria torespon d toa modifie dmediu mcomposition .Thi s allowsth ecos t ofprotei n turnoveri nplan tcell s tob ecorrespondingl y lower thani nbacteria . Thedegradatio n andresynthesi s rateso fRuDPCase ,NO_-reductas ean dothe r enzymes (Table 1)enabl emuc hmor erapi dadaptatio n thani srequire d inmode m agriculturalsystems ,wher emuc ho f thecar e forinterspecifi c competitionha s beentake nove rb y thefarmer ,an dwher ema nals obreed s forbette rvarieties . ForNO~-reductas ean dothe rrapidl yvanishin g enzymes inparticular ,th e degradation rateseem smor e rapid thani srequire d foradaptatio nprocesse s underal lcircumstance s (cf.Schimke , 1969). Iti ssuggeste d thata n artificial reductiono fth erat eo fprotei n turnoverma y increasene tcro p growthrates ,becaus e thecro pmaintenanc e costi slowere dmor e thanth e reductiono fassimilatio ncause db ya decrease d rateo fadaptatio n tochangin g conditions.Complet eremova lo fprotei n turnoverreduce smaintenanc e costb y - 11- about 10m gglucos epe rg dr yweigh tpe rday ,o r 10- 4 0k gcarbohydrate s perhectar epe rday .I ti ssuggeste d thatpartia lo r complete inhibitiono f protein turnoveri nfull-grow n leaves canb eobtaine d fora par t orth e wholegrowin gseaso nb yus eo fchemicals ,phytohormone so rb yplan tbreeding . Varioussubstance shav ebee nshow nt oaffec t therat eo fprotei n synthesis anddegradatio n atdifferen t stages.Chemical s andphytohormone s inhibiting protein turnovershoul db eapplie d insuc ha wa y thatbiosynthesi s ingrowin g partsi sno treduce dan dreallocatio n ofnitrogenou s compounds inth e reproductivephas ei sno thampered .Manipulatin g themaintenanc e respiration costma y alsob eapplicabl e inman y different fieldso fplan tproduction . Therol eo fprotei nturnove ri nplan t resistance againstdiseases ,however , shouldb e studiedcarefully . Maintenance5f._i2n_concentrati.on s Thepresence ,o fa nindiffusibl e ionspecie s inth ecell ,suc ha snegativel y chargedproteins ,cause sconcentratio ngradient so f thediffusibl e ionsacros s thecel lmembran eaccordin g toa "Donnan-equilibrium" .Excep t forth epossibl e costo fmaintainin gth eindiffusibl eion ,maintenanc eo f these concentrations doesno trequir eenerg ybecaus e theelectrochemica lpotentia li s thesam eo n bothside so f themembrane .Diffusio n ofion s through themembran e causesa passive fluxfro man dint o thecell .Th eactua lintracellula r ionconcentration s wouldb estrongl y influencedb y theio ncompositio n of themediu m ifcontrolle d onlyb y the"Donna nequilibrium" .B ymean so factiv e transport systems,tha t moveion sacros sth ecel lmembran e atth eexpens eo fmetaboli cenergy ,cell s maintaincertai nio nconcentration s inthei rcompartments .Thu sth e distributiono fion sbetwee ncytoplas m andenvironmen t usually doesno t correspondwit ha "Donnan-aquilibrium" .Acros sth etonoplas t ofalga lcell s iongradient s arereported ,an d thishold sprobabl y also inhighe rplant s (Hope, 1971,'Anderson , 1972). - 12- Comparedwit h studieso nactiv e transport innerv ean dmuscl e cells little researchha sbeen ,carrie dpu to nplan t cells (Anderson, 1972).N o reportshav ebee n foundo nio nfluxe sacros s cellmembrane si ntissue so f higherplant s invivo .Activ e ionfluxe shav ebee n studied inalga lcell san d indar kgrow ntissue so fhighe rplant sbathin g ina nutrien t solution.Dat a ofactiv e fluxesi nstead y state conditionswer e collected inTabl e 2.I n actualplant s theio nconcentratio n ofxyletnsa pwa s found tob e0. 1t o0. 7 times thato fa norma lnutrien tsolutio n (cf.Milthorp ean dMoorby , 1969), andi ti slikel y thatio nconcentration s arehighe r inintercellula r spaceso f leaves,fro mwher ewate revaporates .Th eio ncompositio n of the liquid in thesespace s isdifferen t fromtha to fa nutrien tsolution ;nevertheles s iti s assumedtha tfluxe sobserve d innutrien t solutiongiv ea fai rimpressio no f theorde ro fmagnitud e offluxe s invivo. • Inautotrophi c cellsin -an defflu xca nb eenhance d 2t o5 fol db y light (e.g. Hope, 1971),bu tonl y fluxesi ndarknes swil l beconsidered ,becaus e thisstud ywa smad e toobtai na nestimat e ofmaintenanc e costo fplan tcell s indarkness .Possibl eextr aexpense si nth eligh tar eneglecte d because the methodemploye d tocomput eth ecro pdail ygros sassimilatio n (cf.D eWit , Brouweran dPennin gd eVries ,1970 ) accounts forthi sdirectl y (Penningd e Vries,1974) . Morei sknow nabou tenerg yexpenditur e foractiv e transportprocesses . Inanima lcell san dmitochondri aio nextrusio no raccumulatio nan dAT P consumptionar eclearl y related (Stein,1967 ;Lehninger , 1970).Extrusio n ofNa + fromth ecel lrequire sabou t IATI 'molecul epe r translocated ion.Thi s transportoccur sb y twomechanisms ,i non eo fwhic huptak e ofK iscouple d toexpor to fN a ina 1:1 relation,an di nth eothe ruptak e ofK forothe r + ions,amin oacid so rglucos e is looselycouple d toN a transport.Anima l mitochondriad ono t accumulateK orN a ,bu tC a and inorganic Par etake n upa ta cos tequivalen t to0. 6 and 1.0AT Pmolecule s respectively (Lehninger, 1970).Highe rplant ssee mt ous edifferen t transportmechanisms :activ eN a Table2 .Som eactiv efluxe sacros splasmalemm a(p )o rtonoplas t (t) indarknes si nstead ystat econditions . flux membrane rate tissuean dconditio n reference 10 mole/cm/se c K influx P 1.4 Avenasativa ,coleoptyle , Piercean d innutrien t solution Higinbotham,1970 + !! ii Na efflux P > 0.3 Cl"influ x P 0.5 II ti K influx t 1.7 II n Na influx t 0.3 II it Cl influx t 0.1 II II K influx P 0.7 Pisumsativum ,epicotyl , Macklonan d innutrien tsolutio n Higinbotham,1970 K influx t 1. H II allions , P 1.3-2.8 Nitellasp . Vredenberg,1972 efflux K influx P 15.-30. Acetabulariasp . Saddler,197 0 Na efflux P 3.-10. i~* II - 13- + ~ effluxha sbee nobserved ,bu t alsoactiv eK andC I influx independento f Na extrusion.Formatio no f these transport systems isofte n inducible (Anderson, 1972).Informatio nabou t theenerg y costo fmovin g ionsacros s plasmoleinxnao rtonoplas ti smainl yqualitativ e (Anderson, 1972),bu t iti s unlikely chatthes eprocesse s aremuc h lessefficien t inplant s than inanimals . Fisheran dHodge s (1969)an dKir k andHanso n (1973)reporte d valueso fC. 6 + . ... toK ionpe rAT Pmolecul e inmaiz emitochondria ,an d such valueswer e also found forerytrocyte s (Lehninger, 1970).Ther e isstil ldiscussio nwhethe r ATP isuse da sa nintermediat e toprovid eenerg y for transport (Anderson, 1972), but thene tcos to fsuc hmechanism s canalway sb eexpresse d inAT Punits ,sinc e finally energyconsumptio ni salway scompetitiv ewit hAT Pproduction . Toobtai na norde ro fmagnitud e of theenerg y consumption foractiv eio n transport inplants ,i ti sassutnnd ,o nbasi so f theinformatio no fTabl e2 , that active fluxesamoun t to 1-2.10 molepe r cm"piasmalensn ape rsec . Furthermore iti sassume d thata considerabl e fraction of this fluxrepresent s coupledactiv etransport ,an d thatpe r active ionmovemen t theenerg yo f 1AT Pmolecul e isrequired .Thu sa nenerg y fluxma yb e consumed equivalent —1 2 2 ... to 1.10 moleAT Ppe rc m plasmaletnmape r sec.Cell swit hdimension so f 4 2 40x40x40u hav eabou t 1.2 10 en plasmalemtnape rg dr yweight ,thu s maintenance ofthes e fluxesconsume sabou t4 rag glucos epe rg dr yweigh tpe r day.I nyoun gan dsmal lcell s thisvalu ema yb e larger,whil e inlarg e parenchyma cells itwil lb e lower.Activ e fluxesacros s thetonoplas tma yb e roughly similar totha tacros s theplasmalemm a (Table 2).Pitma n (1969)o n basiso fsimulation ,conclude d toconsiderabl e activity of the tonoplasti n barley rootcells ,an dLiittge ,Cra m andLatie s (1971)conclude d thatsal t stimulated respirationabov ea sal tconcentratio n of0. 5nMo li srelate d to transportacros s the tonoplast.Withou tmuc hevidenc e iti sassume d thatothe r membranes dono trequir emuc henerg y tomaintai n iongradients ,an d that the costo fre-uptak eo f glucose andamin oacid sleake d from thecel lar e - 14- negligible.Th e total,energ y requirement formaintenanc eo fio ngradient s across thecel lmembrane s isthu sestimate d tob e6-1 0m gglucos epe rg dr y weightpe rday .Thi s figuredepend so n theconcentratio n andconcentratio n gradientmaintaine dan do nmembran epermeability .Probabl ymainl y thelatte r varieswit h tissuean dspecies ,an dth esecon dwit henvironmenta lconditions . Whenth etota lmaintenanc e requirementfo rplan t tissue isabou t 40 mgglucos epe rg dr yweigh tpe rday ,th ecos to fmaintainin g iongradient s corresponds toabou t2 0Z .Thi svalu e isabou t similar totha testimate db y Keynes andKaise l (1954)fo rth erelativ e costo fthi sproces s inrestin gfro g muscle cells.Th erespirator yenerg yi nerytrocyte san d activekidne ycells , however,i srequire dmainl y formaintenanc eo f theio ngradien t (Netter,1969 , pg. 763)an dio nuptak e (Lehninger, 1970,pg .616) ,respectively . Thehig h active fluxesi nAcetabulari a (Table2 )ca nb emaintaine donl y asa resul to fth esmal lsurfac evolum erati oo fth e largecells .Th esurfac e volumerati oo fbacteri ai sver ymuc h larger,an di tca nb e inferred that eitherthei rmembran epermeabilit y or thegradien tmaintaine d ismuc hsmaller . Stouthameran dBettenhause n (1973)observe d thatmaintenanc e respirationi n Azotobacter aerogenes isenhance db yincreasin gNH.C lconcentratio ni nth e medium,bu t thisdi dno toccu ri nAzotobacte rvinelandi ibecaus eo fhighl y impermeablemembrane s (Knowlesan dSmith ,1971) .Thi s differencedemonstrate s thevariabilit y thatexist samon gspecie s inthi srespect . Theus eo fa constan tactiv e transporto fion sacros scel lmembranes , other thant omaintai ncertai nio nconcentrations ,i sunknown .I tha sbee n suggested thatpar to fth euptak eo famin oacid san dglucos eint oanima lcell s iscouple d topassiv eNa + influx (cf.Lehninger , 1970),an dals otha tio n uptakema yb erelate d toprotei nsynthesi sa tmembrane s (Sutcliffe, 1973). It isals opossibl e thatplant shav eno tye tbee nabl e todevelo pmembrane s withmechanism sb ywhic hexclusivel y essential substances aretransported . - 15- 2£llSr_SSiS^S22B£S_2r2££S§£®_§S4_H55teful_res£irationiTher ei sn oindicatio n thata noticeabl eamoun to frespirator y energy isrequire d inplant st o providehea t (excepti na fetj,particula r cases),o rfo rdisplacement s ;ther thano fions .Activ e leafmovement srequir ever y smallamount so fenergy . Therei ssom eindicatio n (Pi.ck.ard,1972 )tha tprotoplasmastreamin gi sno ta separateenerg y requiringprocess ,bu tresult s fromothe rprocesses . Theexistenc eo fwastefu l respirationprocesse s inplant s ("uncoupled respiration"o r"idlin grespiration" )ha sbee n suggested toexplai n unexpectedhig hrespiratio n rates (Beevers,1970 )o rlo wyield s (Tanalca, 1972), hutn oconclusio nevidenc eha sa sye tbee n found.Beevers ;(1970 )suggeste d thata considerabl e fractiono fglucos econsume d inmatur e leavesma yb e degradedb yth epentos ephosphat epathway ,a sa nalternativ e toth eKreb s cycle.Th eMAD?H 2generate db ythi spathwa y ismainl y oxidizedb ycytoplasmi c oxidasesan ddoe sno tyiel dATP .Als oa hig h concentrationo ffatt y acidsi n plant cellsdecrease s theP: 0rati o (Baddelyan dHanson , 1967).However , whether theseexample s indicatea useles sdecreas eo fefficienc y ofsubstrat e utilizationi sdifficul t toasses s sincew ed ono thav ea criterion !fo r usefulnesso fbiochemica lprocesses .I twa ssuggeste d (pg.10 )tha ta par to f protein turnoverma yrepresen ta proces so flittl euse,e.g .th erapi d degradationan dresynthesi so fN0--reductase .Measure da srespiratio nrates , usefulan duseles sprocesse s cannotb edistinguished .Th epresenc eo fwastefu l processesrelate d tobiosynthesi s inrapidl y growingmaiz ean dsunflowe rplant s wasrule dou tearlie r (Penningd eVries. ,1972 ,1974) . MEASUREDMAINTENANC ERESPIRATIO NRATE S Themaintenanc erespiratio nrat eo forgan s thatd ono tgro wo rtranspor t substances canb edetermine ddirectly ,becaus emaintenanc e processes arethe n theonl yprocesse s causingCO -production .Car eshoul db etake ni npreparin g thesample ssinc ecuttin go rslicin gca naffec t theinterna lstructur ean d - 16- (thereby)th emetaboli crat econsiderabl y (Eberhardt,1960 ;MacDonaid , 1968). Somemeasurement sobtaine d inthi swa y (method a)ar epresente d inTabl e3 ; theirvalue s arealway sver ylow . -y Measuringth erat eo fmaintenanc erespiratio no fmetabolieall yactiv e organs isprincipall ymor ecomplicated :maintenanc eprocesse s areseldo mno t accompaniedb ybiosynthesi so fstructura ldr ymatte ro rb y active translocation ofsugar san damin oacids .I f thelatte rprocesse sar estopped ,th erat eo f maintenanceprocesse swil ladjus t itself.Moreover ,th erat eo fprotei n turnoveri nmatur e leavesi sprobabl ymaxima li nth emorning ,afte r theonse t ofligh t(pg .8) ,an di ssensitiv e tochange s inth eenvironment .Fortunatel y proteinmetabolis mi ndarknes s doesno tsee mmuc haltere dunti lnearl y all solublecarbohydrate s areconsume d (James,1953 ;Hellebus tan dBidwell , 1964b). Thisma y last6-2 4hours ,o reve na fe wday si nleave so fsom especie s(James , 1953).Th erespirator yquotien ti nthi sperio d isabou tunity . Onemetho d todetermin eth erat eo fsuga rconsumptio n formaintenanc e processes isb yextrapolatin g therelatio nbetwee ngrowt hrat e (increasei n structuraldr yweight )o rrat eo fexpor to fassimilate san drespiratio n rate tozero .I trequire s thatgrowt han ddegradatio nd ono toccu r simultaneously inth esubjec tconsidere d (cf.Pennin gd eVries , 1974),whil e independence ofth erat eo fmaintenanc eprocesse so ftha to fothe rmetaboli cprocesse si s presupposed.T oavoi dchange s inth esyste mt ob emaintained ,measurement s mayno tb etake nwit h longtim eintervals .Thi sca nb edemonstrate db yplottin g shootrespiratio nrate s (at 10C )o fHelianthu sannuu s (data fromKidd , West andBriggs ,1921 )versu s growthrate sobtaine d during thegrowin gseason : thisyield sa ver ylo wrat eo f4 m g glucosepe rg dr ymatte rpe rday .A neas y way toobtai na rang eo fgrowt hrate swithi non eda ywithou t changing conditions formaintenanc eprocesse s isstil l lacking:althoug h the C0? assimilationrat eca nb echange d instantaneously,th egrowt hrat erespond s slowlydu et oth ebufferin gcapacit y of thepoo lo freserv ecarbohydrate s (DeWi te tal. , 1970;Pennin gd eVries ,1974) .Som edat aobtaine db y this Table3 .Maintenanc e respirationrate sobtaine dwit hvariou smethods . P standsfo rth etissu eprotei nconten t (in% )an dT fo r temperature (indegre e C); theassimilatio nrat ei nth eday s priort omeasuremen t isindicate db yH (high,i nful lsunlight) , _2 M (moderate)o rL (low,a t 100W m orless) .Th e respiration ratei sexpresse d inm gglucos epe rg dr ymatte rpe rday ;value s originallyexpresse di nothe runit swer econverted ,assumin ga respiratoryquotien to f1 . References: 1Hube ran dZiegler ,196 0 2derive d fromYod ae tal. , 1965 3Tandy aan dYamagutchi ,193 3 4KcCree ,197 0 5Thornle y andHesketh ,197 2 6Pennin gd eVries ,197 4 7Pennin gd eVrie san dVa nLaar ,unpublishe d 8 derived fromHeichel ,197 0 9Alberda ,unpublishe d 10Louwerse ,unpublishe d 11Prin zzu rLippe ,195 6 12James ,195 3 Table 3, continued speciesan dorga n conditions maintenance method reference respiration rate Avenasativ aan d waterconten t9-11 % 0.0002-0.0010 a 1 Hordeumvulgare ,seed s Pisumsativum ,seed s airdrie d 0.0039 a 1 variousconifers , core,1*1 5 0.02-0.13 a 2 stemwoo d ii bark,T=1 5 1.3 a 2 Aspergillusniger , T=30,[O ^ «80%, 337. a 3 mycelium nongrowin g Trifoliumrepens , T-20,L 15. b 4 plants Gossipiumsp. ,boll s fieldcondition s 6+10 b 5 Helianthusannuus , P»24,T»18 ,M 28. b 6 plants it p=24,T=25 ,M 47. b 6 «t P=15,T«25 ,M 41. b 6 Zeamays ,plant s P*23,T=18 ,M 7. b 6 II P=23,T=25 ,M 15. b 6 H P=23,T=33 ,M 44. b 6 Helianthusannuus , T=25,H 60. c 7 leaves Zeamays ,leave s T=25,H 40-60. c 7 n T=25,H 57. c 8 it T=25,L 39. c 8 n T=25,L 8-10. c 9 Loliumperenne ,leave s T«25,H 40. c 7 Phaseolusvulgaris , T=25,H 80. c 7 leaves it T=25,L 12. c 10 Phaseolusmultiflorus , leaves, 14day sol d T«18-25 ,L 55. c II 28 " " T"18-25,L 25. c •• 48 «' •» T=18-25,L 18. c II 24 *' " T=20,L,daylength=6hr s 18. c it 24 " " T*20,L,daylength=12hr s 18. c II 24 " " T=20,L,daylength=18hr s 30. c Hordiumsp .an d T=20 50-150 d 12 Triticumsp.,leave s Prunus lauracerasus T=20 10-20 d 12 Zeamays ,leave s T»20,M 27+ 1 0 d 7 it " T-25,M 26+ 1 0 d 7 II I" T=»30,M 46+ 1 0 d 7 Phaseolusvulgaris , T«25,M 27+ 1 0 d 7 leaves - 17- method (b)ar egive ni nTabl e3 .Du e toscatte ri nth emeasuremen tan dwhil e themaintenanc e respiration rateprobabl yba a adiurnal ,patter n thismetho d isno taccurate .Thi sextrapolatio nmetho dha sbee nuse dals o todetermin eth e maintenancerequiremen to fanimal s (Kleiber,1961 )an do fgrowin gbacteria . Sincegrowt han dmaintenanc eprocesse sar eno tindependen t inbacteri a (pg.3 ) the"maintenanc erate "obtaine d inthi swa y isonl yvali d forgrowin gbacteri a (cf. Pirt, 1965). Inhighe rplant s thiscomplicatio n isabsent ,sinc ea tal l growthrate smos tcell s dono t increase instructura ldr yweigh t (totaldr y weightminu s reserve substances);onl y seedlingsma yb ea nexception . Temperaturechange sma yb eusefu li nmodifyin grapidl y therat eo f conversiono freserve s intostructura lmaterial ,an ds ot oextrapolat et o growth ratezero .Bot hth erespons eo f therat eo fbiosyntheti can dmaintenanc e processes totemperatur e should thenb eknown . Anothermetho d (c)measure s therat eo fC0 o production ofattache d organs undercondition swher en ogrowt ho rtranslocatio n isexpecte d tooccur ,bu t maintenancei sstil lunaffected .Thi smetho dha sbee nuse d formatur e leaves after6-2 4 hoursdarkness .Value sobtaine db y thismetho dar esomewha t larger thanthos eobtaine db y (b),bu t afe wver y lowvalue swer e founda swel l (Table 3).Thi smetho d isinaccurat ebecaus e iti sdifficul t toestablis h whetheral lprocesse sexcep tmaintenanc ehav estopped . Afourt hmetho d (d)measure s therat eo frespiratio no r therat eo fdr y weightdecreas eo fful lgrown ,detache dorgans .I f thesear eno texhauste d fromcarbohydrate s therespiratio nrat e isno tmuc h changeddurin g thefirs t fewday s (James,1953) .Woun d respirationfro ma smal lpar to f thelea fo r petiole isunlikel y toinfluenc e therespiratio n ratenoticeably ,s otha t measurements ofleave so fwel lilluminate dplant s for thefirs tda yafte r detachmentprobabl y approximatenorma l rates.Suc hrate s arepresente d inTabl e 3,an dar e aboutsimila rt othos eobtaine db yothe rmethods ;th ehig hvalue s forprimar ybea nleave s (80an d 55)probabl y reflectsom eremaine d - 18- biosyntneticactivity .Th ever yhig h ratesreporte db y James (upt" o150 ) mustb eerroneou ssinc eno tenoug hcarbohydrate s arepresen t tosustai nsuc h highrate sfo r7 days ,a swa sreported . Table3 show sa rang eo fmaintenanc e respiration rateso f8-6 0m gglucos e perg dr yweigh tpe rda ya t25°C .Th einformatio ni sstil l too limitedt o decidewhethe rdifferen tspecie shav edifferen trate so fmaintenanc e respiration undersimila rconditions ,bu ttha to fH .annuu sseem salway shighe r thantha t of2e amays ,A compariso no f thevalue s foron especie s aton e temperature (Table 3)show s thatleave swit hhig hassimilatio n rates in theday sprecedin g themeasuremen thav ehighe rrespiratio n rates than thosewit h low'assimilation rates.Thu sals omeasurement s suggesta relatio nbetwee nmetaboli c activity andmaintenanc e cost.Th epossibilit ymigh tb e investigated thatactiv eio n fluxesacros scel lmembrane srequir epe rg dr yweigh t anamoun to fenerg y independento f theassimilatio n rate*(bu tdependen t ontemperatur ean dsalinity , seebelow) ,whil eprotei n turnoverconsume sa variabl eamount ,whic hequal s 2-7 Zo f thedail ygros sassimilation .Tamiy aan dYamagutch i (1933)describe d acomponen to fmaintenanc erespiratio n related toth egrowt h ratei n Aspergillusnige ro f 12% o fth etota lsubstrat econsumptio n at3 0C an d anoxyge nconcentratio n of8 0% . Therat eo fmaintenanc e respirationpredicte d frombasi cdat aequal s 15-25m gglucos epe rg dr ymatte rpe rday ,an d isabou tcorrec tfo rsom e plantsgrow nunde rmoderat ean d lowlig hintensities ,bu t is toolo wi nothe r cases.I ti ssuggeste d thatthi sshoul db eattribute d to thefac t thatprotei n turnoverrate suse dfo rpredictio nwer eno tobtaine d fromplant s growna t highligh tintensities ,bu tfro mles sactiv eones . Itremain s tob eestablished , however,tha twastefu lrespiratio ndoe sno toccu ri nsuc hleaves . Ina simulatio no fgrowt ho fa maiz ecro pD eWi te tai .(1970 )assume d thatmaintenanc eprocesse s consume 15m gglucos epe rg dr ymatte rwit h4 % nitrogenpe rday .Th esimulate d growth rateagree dwel lwit hobserve drates , 19 whereas a two tritr.eshighe r value underestimated v.hegrowt h rate considerably. The assimilation,rat e simulatedwit h this model, however, is probably too low, «".-,:th e relation ofmetaboli c activity tomaintenanc e cost is presumably more pronounced thanwa s simulated,Kyle , Brocfci.ngton,Powel l ar.dCros s (1973) used a value of 30a) gglucos e per gdr y matter per day to simulate growth of UiViculrr.barle y and obtained an encouraging agreementbetwee n experimental and simulated results. It i.s obvious t'bfttmeasurin g the rate of maintenance respiration is a difficult task, and it isno t apprizing that in spite of the enormous amount of work done onplan t respiratiun only a tew values can be interpreted as tr:ain{eaanc:erespiratio n %i.th reasonable certainty. For abette r understanding of th-ivariou s processes cany observations are scili tob e made, where especially -.'etaboiic activity may be an important reference value. Because r.ha rates of indi\~dualmaintenanc e processes ate variable and because the rcainteuanee rcspitaticn rate is so easily exceeded by that of biosynthetic precedes, it s;ef:astha t themethod s described previously are not suitable for accurate determinations ofmaintenanc e respiration inplants ,an d that this process,snoul d be approached on abiochemica l level instead. EFFECT OF ENVIRONMENTAL FACTORS OHMAINTENANC E PROCESSES To limit this study effects of growth retardantswil l not be covered, but it is well known that these may influence protein synthesis and degradation and decrease the efficiency of oxidative phosphorylation. Also effects of plant disease will not be considered. Numerous;measurement s havebee n made of the effects of environmental factors raplan t and leaf respiration rate?.,aan y ofwhic h are presented in the Encyclopedia of Plant Physiology, volume 12,2. However, frequently the contribution o£C0 „ from biosynthetic processes to the total CO, production isno t known,no r the effect of the changed factor on the rate of these -2 0- biosyntheticprocesses .A sa result ,stil l littlei sknow nabou t theeffect s ofenvironmenta l factorso n therac eo fmaintenanc eprocesses .Measurement s inwhic h thechang eo fa nenvironmenta lconditio n persistsshoul db e distinguished fromshor t termchanges ,becaus eadaptatio nprocesse sma ymodif y theresponse . I^HSSIISJEHI!!* * n s?ite °fth egenera lknowledg e thattemperatur e regulates the rateo fman yprocesses ,suc ha srespiration ,i teffect so nmaintenanc e processeshav ehardl ybee nstudied . Lyonsan dRaiso n (1970)demonstrate d thattemperatur edi dno talte rth e P:0rati oi nisolate dmitochondri ao fsevera lspecie sbetwee n 1.5C an d 25C . Probablybecaus e theprocedur e followed inpreparin gmitochondri awa sno t sufficiently subtle (cf.Rotnan ian d Ozelkok, 1973)absolut evalue s ofth e P:0 ratio'swer e fairly low (1.5).Chillin go fcol dresistan tcucumbe r varietiesdi dno taffec t theP: 0 ratio,whil e itdecrease d from 1.5 to0. 5 innon-resistan tvarietie s (Kushnirenkoe tal.,1969) .Th eP: 0 ratioma y thusb eabou t 3i nth erang eo f temperaturesnorma l toa plant ,bu treduce d atrelativel y higho r lowtemperatures . Therat eo f thermalprotei n turnoverincrease s exponentiallywit h temperature,bu ti ti ssmal la ttemperature snorma lt oth especie sconsidere d (0.013an d0.04 4day" 1 inmammal sa t37 °an d40°C ,respectively ,MorOwitz , 1968).Th eonl ydescritio nfoun do fexperiment s abouteffect so f temperature therat eo factiv eprotei nturnove rconcern sE.coli ,wher e therat eo f on proteindegradatio n increasedexponentiall y fromabou t0. 2 day at25° Ct o about2. 0 day""1a t45°C ;u p to42° Cth erat eo fdegradatio nwa sprobabl y equal totha to fresynthesi s (Pine, 1973).I nchernophli cbacteri a therat eo f protein turnovera t70° Ci sno thighe rtha ntha to raesophylicf bacter a at35° C (Pine, 1972).Simila rexperiment s inhighe rplant shav eno tye tbee nperformed . Theincreas ei nth ediffusio ncoefficien to fion swit h temperature issmal l (about 1.3pe r 10°C),bu tth erespons eo fmembran epermeabilit y to temperature 21- isconsiderabl e inanima lcell s (Stein,1967 )an d inalga e (e.g.Thorhaug , 1971).Hop e (197!)report s thatactiv e fluxesar eenhance d 3t o4 fol dpe r 10C temperature increase ranerv ecells ,an dWaise l (1972)present ssom e indirect evidence fora slightl y smallerrespons e inplants .A largeincreas e ofcos to fmaintenanc eo fio nconcentration s isi nagreemen twit h observations thathig htemperature s amplify thedamagin geffec t ofsaline ,medi a (Strogonov, 1964). The.basi cinformatio nthu ssuggest s that temperature increase raisesth e costo fmaintenanc eb ya considerabl e stimulation ofprotei n turnoveran do f activeio nfluxes . Althougha tth epresen tstag eo fknowledg ea predictio no fho wth e maintenance respiration ratei nhighe rplant s responsquantitativel y toa changei ntemperatur ei so f littlevalue ,th eabov econclusio n seemsconfirme d bydirec trespiratio nmeasurements ,i nwhic hofte na stimulatio n ofC0 „ o productionha sbee nreporte d ofabou t 3fol dpe r 10C temperatur e increase at lowtemperatur e to2 fol da thighe r temperaturesfro mbelo w0 C i nsom e speciesu p to45° Ci nother s (Kidde c a].., 3921;Yamamoto , 1933}Forward , 1960 'fable3) .Unfortunately ,man yo f thesemeasurement swer emad e inshor t termexperiments ,an d thusma yno talway sb e representative for long tern changes (cf.Forward , i960).S ono tonl y therelation sbetx,ree ntemperatur ean d theindividua lmaintenanc eprocesse s arepoorl yunderstood ,bu tals oth e overalleffec to ftemperatur e onmaintenanc e respiration innot .ye twel l established. Respirationrate so fplant so fdifferen tspecie sa t theiroptimu mgrowt h temperatures,whic hma yb e20° Capart ,ar eabou tsiciila r(Forward , 1960),whic h agreeswit h thesuppositio n (pg. 13)tha ta large ,fractio no f themaintenanc e costi srelate d tometaboli c activity. Water stressand_sa lin ity_ .Wate r stressan dsalinit y areconsidere d together becausethes eprocesse shav ea nincrease d ionconcentratio n incell s inccramon . - '}? In spite of the agricultural importance of these factors,ther e is as yet little insight into theireffect s on a physiological or cellular level.Th e influences of salinity onplan t growth have been reviewed recently by Waisel (1972). In mediawit h ahig h salt concentration theP: 0 ratio of isolated mitochondria remains unaffected (e.3. Gr«env;ay and West, 1973). Moroy.ovski and Kabanov (1970) found that the?: 0rati o of a salinity sensitive species did not decrease up toa soil NaCl concentration of 0.6 Z, nnJ that,o f n salt resistant species up to 2 ?.. Also in these cxpfrirrent,? absolute values of the P:0 ratiower e fairly low. A direct i-.i ?.e.c-.t of w-iter ptrcfts on the.efficienc y of oxidative phosphorylation has not been fot:nd. It is therefore expected that water stress and salinity at a level noma! to the species considered do not uncouple oxidative phosphorylation. The activity of rn^nyenzyme s de-creamer,wiu- uvat«* r strero;pi.-rait-.tK ,whil e that of other enzymes remains unaffected (<-.£.Bardzi k ct ol., 1972). Similar responses were observed inplant s atn;»di asalinize d with various salts,bu t naturally the reactions of glycophytes at low salt levels differed from that inhalophyte s (Waisel, 1972). No report has been found about the effect of water stress or salinity on the active fluxes across cell membranes. 03tnotic shrinkage of the cell size did not affect the respiration rate of Azotobacter vinelandii (Knowlcs and Smith, 1971). An increase of the plant salt concentration generally stimulates prccesses for maintenance of ion concentrations (Waisel, 1972), but how soil salinity affects ion gradients across cell mer.branas is still undescribed. It istsos t likely that also the type of salt causing salinity affects the degree of stimulation of these saintenar.ee processes. In case of water stress plant ceilsobtai nSios to f their increase in osnotic potential b" accumulation of inorganic ions (Waisel, 1972). Since then also the salt concentration in the intercellular spaces rises the gradients to be -2 3 maintained increase ifth eio nspecie sacc.iuiular.e di nceil si sdifferen t from that inintercellula rspaces . Iti stherefor eexpecte d thatcontinuou swate r stress reduces therat e ofmaintenanc e respirationmainl yvi aa decrease dplan tmetabii eactivit y (although theturnove r rateo fsom eenzyme sma yb eincreased; ,an d thata shortperio d ofwate rstres smodifie s itonl yslightly .Salinity ,how&ver , canincreas e thecos to fmaintainin g intracellulario nconcentration smarkedly . Thusroot swit ha hig hio nselectio ncapacit y andsal texcretin g leafceils . mayprotec t themajorit y ofcell sagains t thedevelopmen to funnecessar y gradients,an dmaintenanc e cost.Consequentl y both area .face to fplan tpaJ t resistance (cf»Waisel , 1972).T owha texten d salinity increasesth etota l maintenancecos tcanno tye tb eestimated .Rai nwa ydecreas eio nconcentration s inth eintercellula r spaces inleaves; . Again theseill-describe d expectations aresupporte d bydirec t respiration measurements.A nincreasin gwate rshortag ereduce s therat eo flea f maintenancerespiratio n tcles s than5 0 Xo f itsinitia lvalu e (Huberan d Zicgler, 1960;Boyer ,1970 ;Gordo nan dBichurina , 1970); thato foa tseedlings , however,double d (Huberan dZiegler , I960).Rehydratio n increases respiration rates temporarily 2t o6 fol d (Huberan dZiegler , I960),whic hprobabl yresult s fromenzym e inductionan dothe rhiosyntheti cprocesses .Th eenerg y requirement formaintenanc ei nSaccharcmyce s cerevisiae ina 1.M NaC lmediu m is4 time s largertha ni na NaC lfre emediu m (Watson, 1970). Inhalophyte smetaboli c activity isno t lowereda t lowsalinit y levels,whil e respirationseem s stimulated (Waisel, 1972),whic hprovide s indirectevidenc e thatderiv e processes tomaintai nio nconcentration sar eintensified . Starvation fromnutrients_and_cerb<2hvdrates .Zaitsev ae t al. <:970)reporte d thatshor tter mP-deficienc y didno tdecreas e "mitochondrial functioning", although itreinforce da growt hrat ereductio ni nwate r stressed andi n - 24- floodedplant s (Samuilove tal. „ 1970).Whe ngrowt ho fE ,col ian do f Torulopsisutili si slimite db yiro nth eP: 0rati ofall sfro m3 t oabou t 1 (Rainniean dBragg , 1973). Trewavas (1972)foun d thatabsenc e ofN0 ~ P0^~, S0^,Mg~ + or Ca2+ increased therat eo fprotei n turnover inLemn amino r2 t o3 fold .I nS .col i therat eo fproteolysi s isabou tdouble d inamin oaci d starved cells (Pine, 1973).Th eturnove rrat ao fphospholipid s inphosphoru sdeficien tSpirodel a isreduce d (Bieleski, 1972).Syret t (1960)showe d thatdeficienc y ofK +, 2+ 2+ Mg ,an dC a slightLy increased theplan trespiratio n rate,whil e severe deficiency of thesean do fN an do fP decrease dplan tmetaboli cactivit y and respiration. Themai neffec to fsligh tnutrien t deficienciesma yb ea chang e ofth e chemicalcompositio no fbiamas ssynthesized ,a decreas ei nmetaboli cactivity , anda nincrease d rateo fprotei n turnoveran d ofnitroge nredistributio n among plant organs,Whe ngrowt h islimite db ynutrient s therat eo fprotei n turnover isprobabl y increasedan d the.P: 0 ratiodecreased . Starvationof .carbohydrate s inducedb yprolonge d darkness,generall y forcesth ecel lt odegrad eprotei nbecaus e lipidsar eofte npresen t inver y smallamount sonly .Th e term"maintenance "i sconfusin g inthi ssituatio n since theplan tdoe sno tmaintai nit sstructures ,and ,soone ro r later,it s assimilationcapacit ydecreases . Itha softe nbee nobserve d thatplan tproductivit y canb edepreose da t highnigh ttemperature s (e.g.Went , 1957).A trelativel y high temperatures themaintenanc e costi slarg ean dth erat eo fbiosyntheti cprocesse si s stimulated,s otha tth epoo lo freserv ecarbohydrate sma yb edeplete dbefor e theen do f thenigh t (Challa,pers .coram.) .Th eresultin gdamagin geffec t of ahig hnigh ttemperatur e isavoide dwhe n thenigh tperio d issufficientl y shortt opreven te>diaustion ,o rwhe nsufficien t reserves are formedi n daytime.Translocatio no fsuga rfro m leaveso ftomat oplant s stops athig h night temperatures (Kent,1957) ,s otha t carbohydrate starvation in -2 1 heterotrophicpart sresults ,i nspit eo f thepresenc e ofreserve s inth eplant . 9S'BS5J,„£SI1SSB_M25i^£^_e525_SS§„liY_£ShiiSii2B•Th c effectso f awid e range of0 ?an dC O concentrations ondar krespirator y processes are small,i n contrast tothei reffect so nphotorespiration .Th erat e of 0 diffusionint o thick tissuesi susuall y sufficient toavoi d anaerobic conditions (MacDonald, !968).A ta hig h Q7concentratio n (80% )th egrowt hrat e ofyeas t isreduce d (e.g. Tamiyaan dYamagutchi . 1933),possibl y due tostimulatio no fprotei n turnoverb y itsoxidation . Oaonan dU Vradiatio ndestro y cell structures,an d thusstimulat erepai r processes (e.g.Da se tal, , 1972),bu tunde rnorma l conditions theireffect s are.negligibl efo rrespiratio n studies.Eve n inpollute d areas theozo n concentrationremain sgenerall ybelo wa concentratio n thatstimulate smaintena i respirationnoticeabl y (cf.Pel lan dBrennan , 5973). Mechanical stress.A 2- 5fol d stimulation ofrespiratio nha sbee nobserve d in manipulated leavesan dbranches ,i nflutterin g leavesan deve ni n leavesi n anairstrea mbu tfixe do na fram e (Went,1957 ;Eberhardt , I960;Todd ,Chadwic k and1'sai , 1972).Ther ei sa sye tn owa y toexplai nthes e results,Eberhard t (I960)suggeste dtha t it.i sessentiall y thesan ephenomeno na s"woun d respiration",whic h largely consistso fstimulate d biosynthesis.A compariso n ofexperimenta lan dsimulate d resultso fmaiz ecro pgrowth ,wher emechanica l stimulationo fmaintenanc ewa sneglecte d (DeVi t et al., 1970),suggest s that thisphenomeno nhardl y contributes torespiratio ni nfiel d conditions,an di t istherefor eexpecte d that theeffec to fwin doutdoor s ismuc h smaller than measured inshor tterm ,climat e roomexperiments . ACKNOWLEDGEMENTS Mr. B.Boerboo aha smad ea compilatio n ofrelevan t literature ata n early stageo f thisreport .Discussion swit hdr .A.H .Stouthame ran d -26- dr.ir.C.T.d eWi twer emos tvaluabl ean dthei rhel pi sgreatl yappreciated . MissA.II .va nRosser akindl ycorrecte dth eEnglis htext , LITERATURE CITED ANDERSON,W.P.,IO N TRANSPORT INTH ECELL SO F HIGHER PLANTTISSUES . ANN.REV.PLANT PHYSIOL.,23,51-72,1972 BADOELEY,M.S .AN DJ.B.HANSON ,UNCOUPLIN G OFENERGY-LINKE OFUNCTION SO F CORNMITOCHONDRI A BY LINOLEIC ACID AND MONOMETHYLDECENYLSUCCTNIC ACID.PLAN TPHYSIOL.»42»1702-1710,196 7 BAROZIK.J.M.»H.V.MARSHAN DJ.R.HAVIS .EFFECT SO FWATE R STRESSO NTH E ACTIVITIESO FTHRE EENZYME S INMAIZ ESEEDLINGS .PLAN TPHYSIOL . 47,828-831*1971 BEEVERS»H.RESPIRATOR Y METABOLISM INPLANTS .HARPE R ANDROW,NE WYORK . 1961 8EEVERS»H.RESPIRATIO N INPLANT S AND ITSREGULATION . IN PREDICTIONAN O MEASUREMENT OFPHOTOSYNTHETI C PRODUCTIVITY,209-21 4•1970 . 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J.APPL.ECOL.,9,315-317,1972 TODD,G.W. , D.L.CHADWIC K ANDS.D.TSAl ,EFFEC TO FWIN DO NPLAN T RESPIRATION,PHYS.PLANT.,27,342-346,197 £ TRAVIS,R.L.,W.R.JORDA N ANDR.C-HUFFAKER ,EVIDENC EFO RA N INACTIVATING SYSTEM OFNITRAT EREDUCTAS E IN HORDEUM VULGAREL .OURIN G DARKNESSTHA TREQUIRE SPROTEI N SYNTHESIS.PLAN TPHYSIOL . 44,1150-1156,1969 TREWAVAS,A., THETUR NOVE RO FNUCLEI C ACIDS INLEMN AMINOR .PLAN T PHYSIOL. ,45,742-751,1970 TREWAVAS,A.,CONTRO L OF THEPROTEI N TURNOVER RATES INLEMN A MINOR. PLANTPHYSIOL.,49,47-51*197 2 VREDENBERG.W.J.A METHO DFO RMEASURIN G THEKINETIC S OFENERG YDEPENDEN T CHANGES INTH EELECTRICA L MEMBRANE RESISTANCE OFMETABOLIZIN G PLANT CELLS.BIOCH.BIOPHYS.ACTA,274,505-514.197 2 WAISEL,Y .BIOLOG Y OF HALOPHYTES.ACADEMI CPRESS ,LONDON .197 2 WATSON.T.G.,EFFECT SO FSODIU M CHLORIDE ONSTEAD Y STATEGROWT H AND METABOLISM OF SACCHAROMYCES CEREVISIAE.J.GEN.MICROBIOL. . 64,91-99,1970 WENT,F.W. ,TH EEXPERIMENTA L CONTROLO F PLANTGROWTH . CHRONICA BOTANICA,WALTHAM . MASS..USA .195 7 <343PP. " WIT, C.T.DE.R.BROUWE R ANDF.W.T.PENNIN GD EVRIES .TH ESIMULATIO NO F PHOTOSYNTHETIC SYSTEMS. IN PREDICTION ANDMEASUREMEN TO F PHOTOSYNTHETICPRODUCTIVITY ,P G47-69 ,PUDOC *WAGE NtNGF.N ,197 0 YAMAMOTCA.UEBE R DEN EINFLUSS EINIGER GIFTEUN ODE RTEMPERATU RAU FDE N AUSNUTZUNGSGRAD DER ATMUNGSENERGIE 8EIMWACHSTU MDE SSCHIMMEL - PILZES.ACT APHYTOCHIMICA,7(1),65-92,193 3 YODA,K.,K.SHINOZAKI ,H.OGAWA ,K.HOZUM IAN DT.KIRA ,ESTIMATIO N OFTH E TOTAL AMOUNTO F RESPIRATION INWOOD YORGAN SO F TREESAN D FOREST COMMUNITIES.J.BIOL .OSAK A CITYUNIVERSITY , 16,15-26,1965 ZAITSEVA,M.G.,Z.V.TITOV A AND8.SARSENBAEV , PROPERTIESO FMITOCHONDRI A INROOT SO F WHEAT GROWNUNDE R DIFFERENT CONDITIONSO FPHOSPHAT E NUTRITION.SOVIE T PLANTPHYSIOL.»17*819-826,197 0 ZUCKER,M.,LIGH T ANDENZYMES .ANN.REV.PLAN TPHYSIOL.,23,133-156,197 2