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The Effect of Certain Metabolic Inhibitors on Vascular Tissue Differentiation in Isolated Pea Roots Author(S): John G

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The Effect of Certain Metabolic Inhibitors on Vascular Tissue Differentiation in Isolated Pea Roots Author(S): John G The Effect of Certain Metabolic Inhibitors on Vascular Tissue Differentiation in Isolated Pea Roots Author(s): John G. Torrey Source: American Journal of Botany, Vol. 40, No. 7 (Jul., 1953), pp. 525-533 Published by: Botanical Society of America Stable URL: http://www.jstor.org/stable/2438502 . Accessed: 23/08/2011 15:21 Your use of the JSTOR archive indicates your acceptance of the Terms & Conditions of Use, available at . http://www.jstor.org/page/info/about/policies/terms.jsp JSTOR is a not-for-profit service that helps scholars, researchers, and students discover, use, and build upon a wide range of content in a trusted digital archive. We use information technology and tools to increase productivity and facilitate new forms of scholarship. For more information about JSTOR, please contact [email protected]. Botanical Society of America is collaborating with JSTOR to digitize, preserve and extend access to American Journal of Botany. http://www.jstor.org THE EFFECT OF CERTAINMETABOLIC INHIBITORS ON VASCULAR TISSUE DIFFERENTIATION IN ISOLATED PEA ROOTS' JohnG. Torrey THE SEQUENCE of eventsoccurring during cellu- thatthe mechanical inhibition of rootelongation by lar differentiationmay be describedand, to some solidifiedgypsum involved inhibition of cell elon- degree,understood in termsof manifeststructural gation,cell division,and cell differentiation.He changeswhich the individualcell undergoesduring demonstratedthat the high osmoticpressures of its ontogeny. Yet littleis knownconcerning the concentratedsucrose solutionscaused essentially biochemicalprocesses in plant tissues which are similarinhibitions of thesecell processesin these fundamentallyrelated to theseontogenetic changes. roots. Isolated pea root tips,cultured in the dark in a Severalworkers have concernedthemselves with sterilesynthetic nutrient medium, grow in a re- the effectsof chemicalinhibitors on cell elongation produciblemanner, showing usual patternsof tis- and differentiation.Cholodny (1931), in his an- sue differentiation.Inhibition of elongationin cul- alysis of the action of auxin on root elongation, turedroots may be producedby a varietyof meta- suggestedthat applied auxin so speedsup thematu- bolic inhibitorswhich act throughtheir effect on ration of cells that the phase of growthduring biochemicalprocesses essential for normal root whichelongation usually occurs is omitted. Noir- growth. This paper describesthe effectsof three falise (1940) reportedthat treatmentof roots of inhibitors,indole-3-acetic acid, iodoaceticacid, and Vicia faba with relativelyhigh concentrationsof 2,4-dinitrophenolon primaryvascular tissue dif- indoleaceticacid (1:40,000) causes cessation of ferentiationin isolatedpea rootswhich have been mitoticactivity in the apical meristemfollowed by subjected in each case to reagentconcentrations prematurevacuolation of the apical initials. The causing approximately90 per cent inhibitionof rapid appearanceof lignifiedvessels closely adja- rootelongation. The purposeof such a studyis to cent to the apical meristemwas interpretedas an attemptto relatebiochemical processes to theknown accelerationof cellulardifferentiation. Barghoorn anatomicalstages in primaryvascular tissue dif- (1942) was unable to demonstrateany effectof ferentiation. applied 1-prolinein stimulatingprotoxylem dif- Attemptsto relate root elongationand cellular ferentiationin the rootsof beans or cotton. Hay- differentiationhave been made in severalstudies of ward and Blair (1942) illustratedan interesting inhibitedroot elongation. As earlyas 1893 Pfeffer case of naturallyoccurring inhibition of root elon- reportedapparent acceleration of acropetaldiffer- gationin thedormant roots of Valencia orange. In entiationof vasculartissue elements in the rootsof the dormantcondition, the apical meristembe- a numberof plants when root elongationwas in- comes relativelyinactive and reduced. Continued hibitedmechanically by plasterof Paris encasement differentiationof vascular tissues results in the of the root. Using Vicia faba rootsgrown in solid appearanceof matureelements closely adjacent to gypsum,Pfeffer found acropetaldifferentiation of the apical region. The environmentalconditions pittedvessel elements to within1 mm.from the tip normallyinducing this dormant root condition were at the end of 15 days, as comparedto 25-35 mm. reproducedexperimentally by treatmentof theroots in uninhibitedroots. Pfeffer'sfinding has beensub- of Valencia orange seedlingswith high chloride stantiatedby numeroussubsequent workers (Na- solutionsat a high pH. Heimsch(1951) reported thansohn,1898) . More recentlyKojima (1931, thatin rapidlyelongating barley roots, maturation 1933), also usingthe technique of Pfeffer,reported of vascular elementsoccurs at a greaterdistance thatsuch mechanicalpressure inhibits cell division fromthe meristemthan in slowlyelongating roots. in the root tip as early as 16 -hr. afterbeginning In his studiesof mineralnutrition of wheatroots, treatment.In inhibitedroots, xylem elements were Burstrom(1947) showedthat high phosphateen- apparentat an average distanceof 1.4 mm. from hancescell multiplication.Under conditions of low the root apex at the end of one week,while in con- phosphate(1/10,000 M) for 5 days, the number trol roots, xylemwas apparentfirst at 13.7 mm. of cell divisionsin theapical meristemis sufficient- Kojima (1931) pointedout that in termsof posi- ly reducedto resultultimately in the disappearance tion, the inhibitedroots appeared to show accel- of the meristemas the cells are "used up" by elon- erated differentiationof xylemcells, but in terms and differentiation.In this the mer- of age gation case, of cells, cellular differentiationin the in- istem disappears due to an unfavorablebalance hibitedroots was actuallyhindered. He concluded amongcell division,elongation, and differentiation. 1 Receivedfor publication January 30, 1953. Inhibitionof root elongationhas been produced This investigationwas supportedin part by a research by X-irradiation(Smith and Kersten,1942) and grantfrom the NationalInstitutes of Health,Public Health P32 et al., Service. recentlyby radiation from (Mackie The writeris indebtedto Dr. Tova Arzeefor her compe- 1952). In each case an upset in normal differ- tent-technical assistance. entiationprocesses has also been observed. Ac- 525 526 AMERICAN JOURNAL OF BOTANY [Vol.40 cordingto Smithand Kersten,dry seeds of Vicia considerabledistance proximal to the firstmature faba pretreatedwith soft X-rays showed markedly phloem elements. Subsequent centripetaldiffer- inhibitedroot elongation upon germination.Pitted entiationof the primaryxylem progresses without vessel elementswere observedclosely adjacent to interruptionfrom these outer small protoxylem ele- the apical meristemin all treatedroots at the end mentsuntil the completetriarch xylem pattern is of 5 days. The authorsconcluded that in the ab- formed. The level of the firstmature protophloem sence of elongation,only pitted vessel elements are and protoxylemelements can be quite accurately formed. determinedby carefulstudy of serialtransverse sec- In all the cases cited above, inhibitionof root tions. Using the criteria adopted by Heimsch elongation,whether by mechanical or chemical (1951), mature protophloemelements are those means,resulted in the ultimateappearance of ma- identifiedby scarcityof stainablecontents and lack ture vascular elementsmuch closer to the apical of nucleus; matureprotoxylem elements are desig- meristemthan in untreatedroots. Apparently,in nated as thosecontaining no nucleus. Throughout all cases in whichcell divisionsin the meristem these discussions,the term "differentiation"in- ceased, resultingultimately in cessation of root cludes all stages in the ontogenyof the cell from elongation,the differentiationprocesses continued its initial formationat the apical meristemto its uninterruptedin an acropetaldirection. In none ultimatematuration into a characteristicanatomical of thesecases, however,is thereconclusive evidence cell type. Each stage of differentiationmay in it- foreither acceleration or inhibitionof vasculartis- selfcomprise a sequenceof separaterelated events. sue differentiationunder conditionsof root inhi- RESULTS.-The effectivenessof indoleaceticacid bition. as an inhibitorof root elongationwas recognized MATERIALS AND METHODS.-Throughout all ex- by Kogl et al. (1934) soon afterits chemicalisola- periments,sterile root tips excisedfrom 48-hr. ger- tion. Lane (1936), usingAvena seedlings,showed minatedseeds of the gardenpea, Pisum sativum, thatthe inhibition of rootelongation is proportional varietyAlaska (Asgrow strain No. 44007) were to auxin concentration.Subsequent workers have culturedin pea rootmedium (Bonner and Devirian, studied extensivelythe auxin inhibitionof root 1939) in Petridishes in the darkat 26?C. as previ- elongation,but no clear understandingof themech- ously reported(Torrey, 1950). Five or ten mm. anismof its actionhas been achieved. The inhibi- tips were excised asepticallyand transferredim- tory action of iodoaceticacid on root elongation mediatelyto liquid mediumto which appropriate was shownby Albaumand Commoner(1941) who additionsof the inhibitorhad been made. One ml. reportedconsistent inhibition of rootelongation in additionsof the inhibitorsolutions, sterilized by Avena seedlingsgrown in 10-4 M solutionsof Seitz-filtration,were made to 100 ml. amountsof iodoaceticacid. Kandler (1950) recentlyreported the nutrientmedium and thepH was adjustedwith the inhibitionby 2,4-dinitrophenolof root elonga- sterile0.05N
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