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The Relationship between Growth and -3- Content of of Pisum sativum L. Author(s): William L. Pengelly and John G. Torrey Reviewed work(s): Source: Botanical Gazette, Vol. 143, No. 2 (Jun., 1982), pp. 195-200 Published by: The University of Chicago Press Stable URL: http://www.jstor.org/stable/2474706 . Accessed: 03/04/2012 15:52

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http://www.jstor.org BOT. GAZ. 143(2):195-200. 1982. ? 1982 by The Universityof Chicago. All rightsreserved. 0006-8071/82/4302-0004$02.00

THE RELATIONSHIP BETWEEN GROWTH AND INDOLE-3-ACETIC ACID CONTENT OF ROOTS OF PISUM SATIVUM L.

WILLIAM L. PENGELLY1 AND JOHN G. TORREY Cabot Foundation,Harvard University,Petersham, Massachusetts 01366

The indole-3-aceticacid (IAA) contentof roots and shoots of light-grownpea seedlings(Pisizmi sali,zim L. 'Little Marvel') growingat differentrates was studied by radioimmunoassayduring the firstweek of germination.Different growth rates were obtained by daily irrigationwith either deionized water or a dilute Hoagland's mineralnutrient solution. Mineral nutrient-grownroots grew morerapidly, had more lateral roots,and initiatedlateral roots at a greaterdistance fromthe apex than did water-grownroots. Growth kineticswith both treatmentswere biphasic. There was an initial phase of rapid expansion lasting about 3 days duringwhich growth was insensitiveto externalmineral nutrient supply. This was followedby a slowergrowth phase consistingof a balance betweencell divisionand cell expansion.Withholding nutri- ents resultedin the progressiveinhibition of duringthis second phase. At no time did the amount of IAA per gram freshweight or the numberof cells per gram freshweight differ significantly in roots treatedwith water or mineralnutrients, whereas the total amount of IAA per and the total numberor cells per organ were greaterin roots providedwith nutrients.The amount of IAA per gram freshweight changed dramaticallyin roots duringthe firstweek of germination,but this was correlated withchanges in the relativecontributions of cell divisionand cell expansionto freshweight growth rather than to growthrate. By contrast,the amount of IAA per gram freshweight in 3-mmroot tips showed a directrelationship with growthrate. The relationshipbetween IAA contentand growthin whole shoots was qualitativelyand quantitativelysimilar to that foundin whole roots.

Introduction specific radioimmunoassay (RIA) (PENGELLY and The role ofindole-3-acetic acid (IAA) in the growth MEINS 1977). To relate IAA content to growth, and development of roots has been the subject of w e studied the distribution of IAA in the root, considerable controversy.Early bioassays of - changes in IAA content during growthand develop- extracted showed that the amount and distri- ment, and IAA levels in plant material of the same bution of auxin in the root and shoot were similar age growing at differentrates, the latter experi- (THIMANN 1934). More recently, IAA has been mental condition being achieved by varying the determinedin roots by combined gas chromatogra- external mineral nutrient supply. For comparison, phy-mass spectrometry(GC-MS) (BRIDGES, HILL- similar studies with pea shoots were also carried out. MAN, and WILKINS 1973; ELLIOT and GREENWOOD 1974; RIVIER and PILET 1974). A comparison of Material and methods results using GC-MS and bioassay (BRIDGES et al. PLANTS.-Pea seeds (Pisum satizvumL. 'Little 1973; GREENWOODet al. 1973) indicated that, in Marvel,' Asgrow Seed Co., New Haven, Conn.) Zea, amounts of IAA in roots were similar to those were rinsed brieflyin tap water and then surface- in . sterilized for 10 min with a 10%' (wt/vol) filtered THIMANN (1937, 1977) emphasized the greater calcium hypochloritesolution containingeither a few sensitivityof roots than shoots to externallyapplied drops of Tween 80 (Polyoxyethylene [20] sorbitan auxin, the formerresponding to 100-1,000 times monooleate, Fisher Scientific,Springfield, N.J.) or a lower concentrations of IAA applied in solution. small amount of commercial detergent as a surfac- These observations led to the view that auxin rela- tant. The seeds were rinsed four times, soaked for tions are fundamentally differentin the root and 8 h in distilled water, sown in fine-particlewashed shoot, namely, that shoots normally contain sub- river sand (special grade #OON, Kesseli and Morse optimal amounts of IAA and hence are limited in Co., Worcester, Mass.) that had been previously their growth by auxin while roots contain supra- washed with deionized water, and watered thor- optimal amounts of IAA and are actively inhibited oughly wvithdeionized water. The seeds were grown by auxin. in a chamber (Sherer Model CEL 511-38) illumi- In view of the continuinguncertainty surrounding nated with warm-white fluorescent lamps supple- IAA and root growth,we examined in detail the IAA mented with incandescent lamps with an average of content of Pisum sativumroots using a sensitive and ca. 350 ,E m-2 s-. The chamber was operated on a 16-h light-cyclewith temperaturesof 25 C day and I Present address and address for correspondenceand re- prints:W. L. PENGELLY, Departmentof Chemistryand Bio- 19 C dark. On the beginning of day 2 (24-27 h of chemical Sciences, Oregon Graduate Center, 19600 N. W. germination) and daily thereafter,the plants were Walker Road, Beaverton,Oregon 97006. watered with eithera 0.25-strengthHoagland's solu- Manuscript receivedA ugutst1981; revisedmanutscript received tion (HOAGLAND and ARNON 1950) or deionized November1981. water. 195 196 BOTANICAL GAZETTE [JuNE

TISSUE EXTRACTION.-The pea seedlings were (Amersham, ArlingtonHeights, Ill.) and 5.0 ml of harvested and rinsed in distilled water in the dark- containing, per 1 liter, 6 g 2,5-diphenyl- ened laboratory.The cotyledons were removed with (PPO) and 2.5 mg 1, 4-bis-2-(5-phenyloxa- a razor blade at the of their petioles, and the zolyl) (POPOP). remainderof the seedling was bisected into root and Radioactive determinationswere made using the shoot by a single transversecut throughthe cotyle- liquid scintillationmethod in the Isotope Facilities donary node. Root or shoot pieces were blotted dry of the Biological Laboratories, Harvard University, with paper towels, weighed, and immediately im- Cambridge, Massachusetts, and samples were cor- mersed in aqueous methanol (80% vol/vol, ana- rected for quenching by the channels ratio method. lytical reagent grade) prechilled to - 15 C and held The amount of IAA in the extract was determined on ice. by comparing the fraction of [3H]IAA bound with For studies of the IAA content in the root apex, the external standard curve. Assays were validated 12-mm root tips of intact seedlings were sliced into either by comparing the values obtained using dif- 3-mm sections with a razor blade cutter, weighed ferent volumes of the plant extract or by adding rapidly in groups of five, and immersed in the cold internal standards of unlabeled IAA to assays of methanol. Typically, 0.07-2.0 g freshweight of tissue plant extracts (PENGELLY and MEINS 1977). were used for each IAA measurement. Plant tissues CELL COUNTS.-The total cell number per root in 25 volumes of cold methanol were ground for 15 was determined by counting acid-macerated tissue min on ice with a mortar and pestle together with in the microscope. Roots were soaked in a solution a small amount of w ashed and ignited sand of 5%,0(wt/vol) chromiumtrioxide and 5%O(wt/vol) and ca. 105 dpm (6 X 106 Bq) of freshly puri- (FoSKET and TORREY 1969) for fied [5-3H]IAA (27 Ci mmol-1, Schwarz-Mann, 48 h. The tissue-acid mixture was then passed Orangeburg, N.Y.) added for recovery estimates through a no. 18 (0.84 mm i.d.) hypodermic needle (PENGELLY and MEINS 1977). During grinding, a using a 10-mlglass syringeand diluted appropriately second 25 volumes of methanol were added. The with water to give about 50-100 cells per micro- homogenate wvasvacuum filteredin a Buichnerfun- scopic field. Each cell number determinationrepre- nel. The residue was washed twice with 25 volumes sents two or three replicate experiments and the of methanol, scraped fromthe filterpaper, and ho- counting of at least 4,000 cells. mogenized for a second 15 min, firstwith a small amount of methanol to insure complete homogeni- Results zation and then with 50 volumes of methanol. The GROWTH AND THE EFFECT OF MINERAL NUTRI- second homogenate was filteredand washed as the TION.-In preparation for measurements of IAA, first; filtrates and washes were pooled; and the we firststudied the growth of pea seedlings during methanol was removed by rotary evaporation at the firstweek of germination.To compare IAA con- 37 C. The aqueous residue (10-20 ml) was broughtto tent with growth, we wanted to examine plant pH 8.5 with the addition of 10 ml of 0.5 M K2HPO4 tissues of the same age growing at differentrates. and partially purified by repeated diethyl ether- We found that limitingmineral nutrients to seedlings bufferpartitioning (PENGELLY and MEINS 1977) to grown in sand had a marked effecton growth,and yield a final 1.0-ml extract in phosphate-buffered seedlings provided with only deionized water grew saline (PBS; 0.1 M K2HPO4, 0.14 M\1NaCl, pH 8.0). considerably more slowly than those provided with Recovery of radiolabeled tracer averaged ca. 60%'. mineral nutrients(table 1). Both the root and shoot RIA.-Plant extracts in PBS were analyzed for were affected in this way, but the effecton root IAA content by RIA, using a procedure modified growth was most striking. The shoot had greater from PENGELLY and MEINS (1977). The standard fresh weight than roots with water treatment, assay mixtureconsisted of 25 Al of [3H]IAA (3 X 104 whereas root fresh weight was about twice that of dpm), 150 ,u of sample in PBS, and 25 ,u of anti-IAA the shoot w ith nutrienttreatment. At no time during antiserum previously diluted with PBS to give a the firstwveek of germinationdid seedlings provided finalantiserum dilution in the assay of 1/200. Tissue only water show any obvious symptoms of mineral extracts were assayed in replicate tubes containing deficiencyother than a reduced rate of development, 10-150 ,ulof the plant extract and 140-0 4ul,respec- and water-grownseedlings would resume vigorous tively,of PBS. Assays of 0, 0.2, 0.5, 1, 2, 5, 10, and 20 growth when provided mineral nutrients (data not ng IAA in 150 ,ulof PBS were used as external stan- shown). dards. The solutions were mixed and incubated for The effectof mineral nutrientson root formwas 1 h at 4 C in the dark. The IAA-antibody complex also striking. After 7 days of germination, roots that formswas precipitated by the addition of 200 4ul provided mineral nutrientswere about three times of saturated (NH4)2SO4 with mixing, and the solu- longer than those provided water (table 1). Lateral tions were cleared by centrifugationat 2,000 g for roots were more numerous and larger, and the dis- 40 min at 4 C. Aliquots of 100 4ulof the supernatant tance fromthe apex to the nearest was were mixed with 1.1 ml NCS tissue solubilizer increased wNithmineral nutrienttreatment (table 1). 1982] PENGELLY & TORREY-IAA RELATIONS IN PEA ROOTS 197

TABLE 1 THE EFFECT OF MINERAL NUTRIENT TREATMENT ON THE GROWTH AND DEVELOPMENT OF PEA SEEDLINGS GROWN FOR 7 DAYS WITH DEIONIZED WATER OR A 0.25-STRENGTH HOAGLAND'S SOLUTION

Shoot Root Root/shoot Tap root Numberof lateral Distance fromroot freshweight freshweight weight length roots > 1 mm tip to nearest Treatment (mg) (mg) ratio (mm) long lateral root (mm)

H20 ...... 157 ? 6 (46) 125 ?4 (63) .80 33+1 (64) 8.7?1.0 (20) 20?1 (20) Hoagland...... 238 ? 6 (38) 468 ?16 (42) 1.97 88 ? 2 (67) 27.3 + .8 (20) 48 ? 2 (20)

NOTE.-Valuesexpressed ? standarderror; sample numbers in parentheses.

Logarithmicgrowth curves show that root growth rate was biphasic during the firstweek of germina- tion (fig. 1). The rate of tissue doubling, which is E 9 directly proportional to the slope of the semi- U T logarithmicplot, was greatest during the first3 days _5-S ~~~~~-F i and was roughly the same for water and mineral nutrienttreatments. After 3 days, root growth rate w 4 _-/ declined with both treatments. Water-grown roots grew much more slowly than nutrient-treatedroots during this second growthphase. cn Growth curves for shoots show a similar biphasic 3-/ course (fig. 2). As with root growth, only shoot w growthin the second phase was affectedby mineral I -^/ of mineral nutrient supply. However, the effect 01~~~~ nutrientsappeared about a day later in shoots than in roots, and the differencebetween growth rates during the second phase was less than found for roots.

7 0 1 2 3 4 5 6 7 DAYS OF GERMINATION 6 A FIG. 2.-Increase in freshweight of water-grown(A) and os T /T/ Hoagland-grown(0) pea shoots. Arrowsas in fig.1. 5 -~T Cell countsof wholeroots were performed at dif- ferentstages of germinationin orderto determine the relationshipbetween cell enlargementand cell 0~~ i3 4 divisionduring different growth phases. The root I) cell numberincreased through the first5 days of germinationwith both water and mineralnutrient (f3 treatment(fig. 3). An increasein cell numberwas notedas earlyas day 1, indicatingthat cell division LLJ beginsearly in germination,although at a low rate. By day 3, c2 Go/! water-treatedroots contained 10%o fewer cells on the average than roots providedmineral ,,,~~~~~3 _ nutrients,and this differenceincreased to 30%0by day 5. On the otherhand, little or no differencebe- tweentreatments was notedwhen results were cal- culated on a cell per milligramfresh weight basis (fig.3). During the first3 days therewas a rapid OO 2 3 4 5 6 7 declinein the numberof cells per milligramfresh weight,indicating that growth was based largelyon DAYS OF GERMINATION cell enlargement.However, there was little or no changebetween days 3 and 5, indicatingthat growth FIG. 1.-Increase in freshweight of water-grown(0) and Hoagland-grown(0) pea roots. Arrows: S, end of soaking duringthe secondphase consistedof a balance be- period; T, beginningof differentnutrient treatments. tweencell enlargementand cell division. 198 BOTANICAL GAZETTE [JUNE

An importantquestion is whetherdifferences in levels in roots and shoots treatedwith water or cell-divisionfrequencies were the result of an activa- mineralnutrient solutions were measured at different tion of cell divisionwhen nutrientswere supplied stages of germinationby RIA. The IAA measure- or an inhibitionof cell divisionwhen nutrients were mentsare expressedin twoways. First, IAA content withheld.To distinguishbetween these possibilities, is expressedas the average amount per unit of cell numberswere comparedbefore and afterdif- tissue weight,i.e., nanogramIAA per gram fresh ferencesin treatmentwere initiated. When cell weight.This formof expressionrepresents an at- numberis plotted semilogarithmically,the values temptto approximateIAA concentrationand, hence, for nutrient-treatedroots at 3 and 5 days (after hormoneactivity. However, because weight changes differenttreatments were initiated) fall on the same duringgermination, this form of expressiondoes not line as values obtainedat 8 h and 1 day (before reflectthe net changein the amountof IAA in the differenttreatments were initiated),whereas those organ. Therefore,IAA measurementsare also forwater-treated roots at 3 and 5 days fall below expressedas the total amountof IAA per root or this line,the deviationfrom the linearrelationship shoot. increasingprogressively with time (fig. 4). These The IAA contentof roots changes dramatically results indicate that mineral nutrientsdo not during the firstweek of germination(table 2). changethe rate of cell divisionbut appear instead to helpmaintain an exponentialrate of cell division whichbegins very early in germination,while nutri- 6.5, entdeprivation appears to resultin progressiveinhi- bitionof cell division. S T 0 IAA LEVELS IN ROOTS AND SHOOTS.-The IAA 0 6.3 / S T 0 -

2~~~~~~~~~~ i 6.1 0o - 0~~0 0 z j 5.9 7 FIG 3. Changein6 0 ~~~~~~~~~E3 w Q~~~~~~~~~~ O0 _j ~~~~~~0 Cl) w _ o 5.7 _

01 I1 5.5 l I O I 2 3 4 5 0 1 2 3 4 5 DAYS OF GERMINATION FIG. 3.-Change in thenumber of cells per root (O0 ) and the number of cells per milligramfresh weight (AA) in DAYS OF GERMINATION water-grown(OA) and Hoagland-grown(GA) pea roots. FIG. 4.-Change in cell number of water-grown(0) and Arrowsas in fig.1. Hoagland-grown(0) pea roots. Arrowsas in fig.1.

TABLE 2 IAA CONTENT OF PEA ROOTS TREATED WITH 0.25-STRENGTH HOAGLAND'S SOLUTION OR DEIONIZED WATER ONLY

IAA CONTENT

FRESE WEIGET ng/gfresh wt ng/root GERMINATION (days) H2O Hoagland H20 Hoagland H20 Hoagland

1/3a ...... 4.6 t.1(64)b 220 ? 36 (4)c 1t.03 17 (4) 2...... 31?1 (96) 38?1 (73) 46+3 (3) 51+3 (3) 1.48? .13 (3) 1.94 .11 (3) 3 ...... 73 + 2 (51) 79 ? 2 (36) 60 ? 7 (3) 66?9 (4) 4.34? .69 (3) 5.22 + .57 (4) 7...... 125?4 (63) 468?16 (42) 38?5 (5) 36?5 (5) 5.00?1.08 (5) 14.6 ?1.97 (5)

a 1/3-dayvalues represent samples taken immediately following the 8-hsoaking; therefore, there is no differencein treatment. b Growthvalues expressed ? standarderror (no.), whereno. = thenumber of roots weighed. e IAA valuesexpressed ? standarderror (no.), whereno. = thenumber of separate experiments. 1982] PENGELLY & TORREY-IAA RELATIONS IN PEA ROOTS 199

Expressedon a freshweight basis, IAA levels de- highest amount of IAA of any segmenttested, clined from220 to about 50 ng/gduring the first whereasthe same segmentin the water-treatedroot 2 days. Thereafter,however, IAA levels were in a containedthe least (fig. 5). Thus, the amount of relativelynarrow range between30 and 70 ng/g. IAA per gramfresh weight correlated with growth Measurementsmade between3 and 7 days werein ratewhen the apical regionof the root was examined. this same range,indicating that IAA levels remain For comparison,we also measuredthe IAA levels relativelystable followingthe initialrapid decline in 7-day-oldshoots (table 3). We foundthat IAA (data not shown). Significantdifferences between levels in the shoot,expressed on a freshweight or mineralnutrient and water treatmentswere not per shootbasis, fell in the same rangefound for the found, however, despite marked differencesin root. Also, differencesin IAA content between growthrate. water and mineralnutrient treatments were small Althoughthe amountof IAA per unit of tissue when expressedon a freshweight basis, but large weightdid not reflectdifferences in growthrate w"Thenexpressed on a per shootbasis. when the whole root was measured,the question ariseswhether IAA concentrationsdiffer locally in Discussion the growingregion of the root.To answerthis ques- There existsan extensiveliterature on effortsto tion,we dividedthe apical 12 mm of the primary determinethe relationshipbetween root or shoot root into 3-mmsegments and measuredthe IAA growthand endogenoushormone levels in a number contentof these segments individually. When results of differentplants (THIMANN 1977; JACOBS 1980). wereexpressed on a freshweight basis, the highest One difficultyhas been the insensitivityand unreli- IAA level was foundin the terminal3-mm segment abilityof biologicaland chemicalmethods of assay. whichcontains the ;and, withthe excep- Thus, therehas been considerabledoubt about the tionof roughlyequal levelsin the secondand third naturaloccurrence of IAA in rootsduring the past segments,IAA levels in subapical segmentsde- 25 yr (SCOTT 1972). Withthe availabilityof analyt- clined progressivelywith increasingdistance from ical methodsdependent on GC-MS determinations, the apex (fig. 5). In each respectivesegment we the reliabilityof chemical analysis was met, but foundIAA levelsto be higherwith mineral nutrient, assaysdepended on extractionof such large amounts as comparedwith water treatment. When the total of tissuethat experimentswlere difficult to perform IAA contentper segmentwas calculated,the apical or determinationsof timecourses of changinghor- segmentof the nutrient-treatedroot containedthe mone levels were cumbersomeand discouraging. The RIA method,with the advantageof specificity 400 and sensitivity,can be performedrapidly on 1 g 1.0- freshw,eight or less of tissue.The comparabilityof resultswith GC-MS and the RIA methodhas now been demonstrated(PENGELLY, BANDURSKI, and SCHULZE 1981), and the RIA methodcan be used 300 -0.8- reliablyto measureIAA in large numbersof rela- tivelysmall tissue samples.

C The resultsreported here show that IAA levelsin 0 pea roots are roughlythe same as in the shoot, fallingin a rangebetween 10-7 and 10-6 M on a fresh weightbasis. These values are similarto those for Zea mays roots,both writhbioassay (GREENWOOD 0.2 et al. 1973) and wi-ithGC-MS (BRIDGES et al. 1973;

2000 N N TABLE 3

IAA CONTENT OF WHOLE SHOOTS OF 7-DAY-OLD PEA SEEDLINGS TREATED WITH 0.25-STRENGTH HOAG- LAND S SOLUTION OR DEIONIZED WATER

0 3 6 9 12 0 3 6 9 12 FRESH IAA CONTENT mm from Apex WEIGHT TREATMENT (mg) ng/g fresh wt. ng/shoot FIG. 5. IAA concentration(A) and total IAA content(B) of 3-mmsegments from 7-day-old pea root tips treatedwith H20 . 138 +4 (20)a 44+3 (3)b 6.1+ .6 (3) deionized water (stippledbars) or Hoagland's solution (open Hoagland.... 215? 7 (12) 53+ 5 (3) 12.0? 1.2 (3) bars). Errorbars forthe apical segment(0-3 mm) indicatethe standard error for four experiments.Error bars for the aGrowth values expressed + standard error (no.), where no. = the num- remainderof the segments(3-12 mm) indicate the deviation ber of shoots assayed in three experiments. b IAA values expressed + standard error (no.), where no. = the number fromthe mean fortwo experiments. of separate experiments. 200 BOTANICAL GAZETTE

RIVIER and PILET 1974). THIMANN (1934) had in growthrate. Thus, strikinglocal differencesin shownby bioassay that auxin levels in roots and IAA concentrationwere not detected when the coleoptilesof A venaseedlings were very similar, and amountof IAA perunit of fresh weight was averaged GREENWOODet al. (1973) obtainedcomparable re- overthe wholeorgan. sults for IAA using bioassay of partiallypurified The reasonfor this appears to be that a balance extractsof Zea mays roots and coleoptiles.Thus, between cell division and cell enlargementwas thereappears to be littledoubt that rootscontain maintainedindependent of nutrientsupply. Al- IAA in amountscomparable to the shoot.The con- thoughcell divisionfrequencies were greater in roots sistencyof resultsobtained with different methods growingin mineralnutrient solution than in de- greatlystrengthens this conclusion. ionizedwater, the numberof cells per unit of fresh Fromthe data presentedhere in whichpea seed- weightwas about the same in the two treatments. lingsgrowing under two quite differentconditions We founda strongcorrelation between IAA content are compared,the followingobservations and con- and cell divisionactivity, as evidencedby highIAA clusions can be made. Seedling growthrate in levels in the root tip whichcontains the meristem mineralnutrient solutions was much greaterthan and by the parallelbetween cell divisionfrequency in deionizedwater. The total amountof IAA per and changes in the total IAA contentper root. seedlingwas also greaterin mineralnutrient solution Changesin IAA "concentration"of the wholeroot, than in water,indicating a directrelationship be- however,were not relatedto cell divisionfrequency tweenIAA contentand growthrate. but were correlatedinstead with changes in the When the freshweight growth of roots (R) and relativecontribution of cell divisionand cell en- shoots (S) treatedwith mineralnutrients (n) or largementto freshweight growth. During the first deionizedwater (w) are compared,relative growth 3 days of germination,growth resulted primarily ranksas follows: fromcell enlargement,and both the numberof cells per gramfresh weight and the amountof IAA per R, > S, > Sw> Rw. gram freshweight declined dramatically. After 3 days,however, growth depended on the rate of cell Whenthe IAA contentsof the differentorgans are division and both the numberof cells per gram comparedinstead of growth,this same seriesis ob- freshweight and the amountof IAA per gramfresh tained.Thus, the directrelationship between IAA weightstabilized. Thus, the IAA concentrationof contentand growthappears to be independentof whole roots seems to reflectthe stage of growth organtype. and developmentrather than growth rate. This directrelationship between IAA contentand Our measurementsof endogenousIAA contentin growthdepends on how IAA measurementsare pea seedlingsdo not supportthe view that auxin expressed.When the concentrationof IAA in whole relationsare fundamentallydifferent in roots and organsis estimatedon a freshweight basis and is shoots. We found that IAA contentwas directly used forcomparison instead of the total amountof related to growthrate, and this relationshipwas IAA per organ,then root and shoot IAA contents independentof organtype. wereabout the samewith water or mineralnutrient treatment,and no relationshipwith growthrate Acknowledgment was seen. On the otherhand, when the roottip was This researchwas supportedby the Maria Moors considered,IAA concentrationdiffered markedly Cabot Foundation for Botanical Research of with treatmentin roughproportion to differences HarvardUniversity.

LITERATURE CITED

BRIDGES, I. G., J. R. HILLMAN, and M. B. WILKINS. 1973. PENGELLY, W. L., R. S. BANDURSKI, and A. SCHULZE. 1981. Identificationand localizationof auxin in primaryroots of Validation of a radioimmunoassayfor indole-3-aceticacid Zea maysby mass spectrometry.Planta 115:189-192. using gas chromatography-selectedion monitoring-mass ELLIOT, M. C., and M. S. GREENWOOD. 1974. Indol-3yl- spectrometry.Plant Physiol. 68:96-98. acetic acid in roots of Zea mays. Phytochemistry13:239- PENGELLY, W. L., and F. MEINS, JR. 1977. A specificradio- 241. immunoassayfor nanogram quantities of the auxin,indole- FOSKET, D. E., and J. G. TORREY. 1969. Hormonalcontrol of 3-acetic acid. Planta 136:173-180. cell proliferationand differentiationin cultured RIVIER, L., and P.-E. PILET. 1974. Indolyl-3-aceticacid in cap tissues of Glycinemax var. Biloxi. Plant Physiol. 44:871- and apex of maize roots: identificationand quantification 880. by mass fragmentography.Planta 120:107-112. SCOTT, T. K. 1972. and roots. Annu. Rev. Plant GREENWOOD, M. S., J. R. HILLMAN, S. SHAW, and M. B. Physiol. 23:235-258. WILKINS. 1973. Localization and identificationof auxin in THIMANN, K. V. 1934. Studies on the growthhormone of rootsof Zea mays. Planta 109:369-374. plants. VI. The distributionof growthsubstance in plant HOAGLAND, D. R., and D. I. ARNON. 1950. The water culture tissues.J. Gen. Physiol. 18:23-24. method for growingplants without soil. California Agr. --. 1937. On the nature of inhibitionscaused by auxin. Exp. Station Circ. 347. Amer.J. Bot. 24:407-412. JACOBS, W. P. 1980. Plant hormonesand . --. 1977. action in the whole life of plants. CambridgeUniversity Press, Cambridge. Universityof MassachusettsPress, Amherst.