Abscisic Acid Stimulation of the Formation of an Ageing-specific Nuclease in Avena Leaves

In excised Avena leaves, depending on the duration of treatment,abscisic acid (10^–5 M) had two distinctly different effectson the level of individual nucleases. In short-term experiments(3-h treatment, abscisic acid increased the level of a relativelypurine (guanine)-specific ribonuclease, in comparison with thewater control. Accumulation of the abscisie acid-induced ribonuclease,however, levelled off rapidly during incubation and the amountof the enzyme approached a plateau in about 6 h. As the accumulationof this ribonuclease became retarded, abscisic acid induceda striking increase in the level of another nuclease, an enzymenon-specific in relation to the sugar moiety but exhibitinga relative adenine specificity. This latter nuclease also wasshown to accumulate slowly in intact Avena leaves during ‘natural’senescence. The Avena leaves contain, in small concentrations,a chromatographic variant of the sugar non-specific nuclease.This minor variant, despite its identical enzymological properties,was found to be physiologically different from the main componentin that its concentration did not depend on the age of the tissuesand was not affected by abscisic acid.     

The in vitro simulation of IAA-induced modification of Avena cell wall polysaccharides by an exo-glucanase

Treatment of Avena coloeptile segments with auxin promotes adecrease in the noncellulosic glucose component of the cellwalls. The decrease in glucan may be simulated in these cellwalls in vitro by an exo-glucanase which produces glucose directlyas the sole reaction product. These results also reveal thatglucans of Avena cell wall polysaccharides are readily susceptibleto exo-enzyme attack. Nojirimycin, a potent inhibitor of ß-glucosidasesand exo-glucanases, inhibits the enzymatic release of glucosefrom Avena cell walls in vitro. Since nojirimycin inhibits IAA-inducedgrowth of Avena coleoptiles, the evidence presented supportsthe hypothesis that IAA-induced growth may be mediated by anexo-glucanase. (Received February 14, 1975; )     

Growth Accelerators and Inhibitors in Lemon Buds Infested by Aceria sheldoni (Ewing) (Acarina: Eriophyidae)

The biological activities of growth accelerators and inhibitorsin lemon buds both infested and uninfested with the citrus budmite, Aceria sheldoni (Ewing), were examined by the Avena test.The growth-promoting activity of the purified ether extractcontaining the auxin was diminished in proportion to the degreeof infestation. Paper chromatography fractions of extracts obtainedfrom infested buds exhibited a strong inhibiting activity onAvena coleoptile elongation in the presence of 0.1 ppm indol-3yl-aceticacid. This inhibiting activity seems to be due to the presenceof a high level of phenolic compounds. The phenol level andits biological activity in both infested and uninfested budswere examined. Infested buds exhibited a higher amount of phenolsthan uninfested ones, the level of the phenols increasing withbud age. The phenols from infested buds inhibited Avena coleoptileelongation to a much greater extent than those from uninfestedbuds. Our results suggest that the presence of the citrus budmite in lemon buds can increase the level of phenols and possiblyother growth depressors in the buds, and that they, in turn,may cause the observed inhibition of growth and developmentof the infested citrus plant.     

Effect of Thiolactomycin on Lipid Synthesis in Higher Plants

The effect of thiolactomycin (TLM), an inhibitor of type IIfatty acid synthase, on lipid synthesis in greening tissueswas examined. Pulse-chase experiments with Na[1-¹⁴C]acetatefor greening Avena leaves showed that continuous administrationof TLM (100µg/ml) decisively reduced phosphatidylcholine(PC) synthesis from acetate and blocked the subsequent conversionof PC to monogalactocyldiacylglycerol (MGDG), whereas temporaladministration of TLM (100 µ/ml) reduced PC synthesisfrom acetate by only 50% and did not block the conversion ofPC to MGDG. In the reduced PC synthesis, the ratio of oleicto palmitic acid decreased at earlier stages of greening, reflectingmore suppression of oleic acid synthesis. In later greeningstages the modulated fatty acid composition recovered to thenormal composition. In further steps, the fatty acid compositionwas not affected by TLM throughout the greening stages. Greeningof either etiolated Avena leaves or etiolated Brassica cotyledonsin the presence of TLM led to a marked decrease in the contentsof MGDG, digalactosyldiacylglycerol (DGDG) and phosphatidylglycerol(PG), but only a small change in the fatty acid compositionof their lipids. The only inhibition characteristic of TLM wasthe desaturation of palmitic to 3-trans-hexadecenoic acid inAvena leaf PG. These results suggest the presence of a mechanismby which the modulated fatty acid composition of lipids is normalizedin the flow of the synthesis. Electron microscopic observationsshowed that Avena chloroplasts developed into round forms ratherthan normal ellipse forms and the thylakoid membranes of Brassicachloroplasts were abnormally swollen everywhere in the presenceof TLM. Photosynthetic oxygen evolution in both tissues wasnot inhibited. (Received December 26, 1986; Accepted April 24, 1987)     

Effect of Peeling on IAA-induced Growth in Avena Coleoptiles

The act of peeling removes the epidermis exclusively from Avenacoleoptiles. Peeling inhibits IAA-induced growth, by inhibitingthe growth of segments incubated in the presence of IAA, andpromoting that of those incubated in water. The magnitude ofthe inhibition of IAA-induced growth is proportional to theamount of epidermis removed. It is shown that neither lateralswelling, wounding, anaerobiosis, nor exposure to supraoptimalconcentrations of IAA cause the inhibition. It is concludedthat in Avena coleoptiles the epidermis regulates the rate ofexpansion of the underlying parenchyma cells and is the principaltarget of IAA-action. Avena sativa L., oat, coleoptile, indol-3-ylacetic acid, auxin, extension growth     

Relationship between hormone content and autonomy in various autonomous tobacco cells cultured in suspension

Various autonomous cultured tobacco cells including crown gallwere examined for their contents of growth regulators by meansof Avena curvature test, cell-division induction test, and tobaccopith callus test. The crown gall cells derived from cv. Hicks produced auxin andcytokinin in the high levels of 300–500 µg IAA equivalentsand 40–80 µg kinetin equivalents per kg, respectively.The major auxin was identified as indole-3-acetic acid basedon mass spectrometry and gas chromatography. These cells alsoproduced methyl indole-3-acetate as a minor component. One ofthe cytokinins was identified as ribosyl-trans-zeatin by meansof both gas chromatography-mass spectrometry and high performanceliquid chromatography. Auxin and cytokinin activities were not detected in the followingthree suspension cultured tobacco cells: cells requiring neithercytokinin nor auxin derived from the callus of N. tabacum cv.Bright Yellow and cells requiring auxin but not cytokinin derivedfrom the calluses of cv. Bright Yellow and cv. Hicks. Theirauxin and cytokinin contents per kg were less than 1 µgIAA equivalent and less than 0.1 µg kinetin equivalent,respectively. The results obtained in this study indicate that enhanced hormonalcontent is not the only reason for autonomous growth. (Received August 16, 1979; )     

Growth Substance Interactions during Uptake by Coleoptile Segments of Avena sativa and Hypocoty1 Segments of Phaseolus radiatus

Further studies have been made on the interactions of plant-growthregulators during uptake by Avena sativa coleoptile and Phaseolusradiatus hypocotyl segments. 2, 4-Dichlorophenoxyacetic acid(2, 4-D) had no effect on the uptake of either indol-3yl-aceticacid (IAA) or -naphthylacetic acid (NAA) by Avena. On the otherhand, a-(i-naphthylmethylthio)-propionic acid (NMSP) stronglyinhibited IAA uptake non-competitively but was much less effectiveon NAA uptake by Avena. The ‘metabolic’ uptake ofIAA by hypocotyl segments of Phaseolus radiatus was very stronglyinhibited by 2, 3, 5-tri-iodobenzoic acid (TIBA).     

Some Growth Regulators of Tobacco in Relation to the Symptoms of the Physiological Disease 'Frenching'

Extracrts of the shoot tips of normal and ‘frenched’tobacco plants were chemically separated into acidic, neutral,and basic ether–soluble fractions. On chromatograms ofthese, some plant growth regulators were assayed using the Avenacoleoptile section extension test. The acidic auxins and an acids and a neutral growth inhibitorwere found. One auxin, with the samew R_F value as indole-3-aceticacid, was four times more concentrated on normal as in ‘frenched’plants. No differences could be established between the twotypes of plants in regard to other growth regulators detected. It is argued that the symptoms of the physiological disease‘frenching’ could be explained in terms of a auxindeficiency.     

Studies on Plant Growth Hormones: II. FURTHER BIOLOGICAL PROPERTIES OF 3-INDOLYLACETONITRILE

1. 3-Indolylacetonitrile is more active than 3-indolylacetic acidin the Avena straight-growth test, but less active in the Avenacurvature test at comparable concentrations. Reasons for thisare discussed, and results of previous work on plant extractsusing the curvature test as a means of assay are considered.
2. Transport of both the acid and the nitrile is polar, fromapexto base of the coleoptile. The nitrile can reach the growingcells as easily, and possibly more easily, than the acid. Thesignificance of these findings for a theory on the mechanismof action of the nitrile is discussed.
3. The nitrile is inactivein the pea curvature test and straight-growthof pea stem sectionsexcept at high concentrations. It is alsoinactive or only slightlyactive in lateral bud inhibition,root initiation, and petioleabscission at the concentrationstested.
4. It is less activethan the acid in root inhibition in cress,but approximatelyas active in Avena. It is approximately asactive as the acidin parthenocarpic fruit development, andinitiation of cambialactivity.
5. The significance of these results is discussed.

     

Studies on Plant Growth Hormones: I. BIOLOGICAL ACTIVITIES OF 3-INDOLYLACETALDEHYDE AND 3-INDOLYLACETONITRILE

1. Two neutral plant hormones, one isolated recently from plants(3-indolylacetonitrile) and the other (3-indolylacetaldehyde)reported to be present in plants, are avaible as pure syntheticcompounds for investigation of their biological activities.This paper is mainly concerned with their effects on cellelongationin the Avena coleoptile
2. 3-Indolylacetaldehyde is considerablyless active than 3-indolylaceticacid in the Avena straight-growthtest; for example, a 1.0 mg./l.solution of the aldehyde showsan activity equivalent to thatof a 0.1 mg./l. solution of theacid
3. An acidic substance is produced in solutions of the aldehydeduring the period of assay. In some experiments it accountsfor all of the activity shown by the aldehyde solutions, onthe assumption that it is 3-indoylacetic acid, and in otherexperiments it shows a greater activity than that of the aldehydesolutions from which it was obtained. Therefore, it is concludedthat 3-indolylacetaldehyde, itself is either inactive or inhibitory.Acid production in aldehyde solutions in vitro is much lower,a fact which suggests that there is enzymatic oxidation of aldehydeto acid in the presence of coleoptiles.
4. The activities of3-indolylacetaldehyde in the pea test andin root-inhibitionand of 3-indolylacetone in the straight-growthtest are brieflyreported.
5. 3-Indolylacetonitrile is considerably more activethan 3-indolylaceaticacid in the Avena straight-growth test;for erample, a 0.1 mg./l.solution of the nitrile shows an activityequivalent to a 1.0mg./l. solution of the acid. The inhibitoryeffect at concentrationsabove 1.0–10.0 mg./l. is lesswith the nitrile than withthe acid.
6. There is negligible productionof acid in solutions of the nitrileboth in vitro and in thepresence of Avena coleoptiles at temperaturesranging from –18?to 25? C. for varying lengths of time.The possibility of enzymaticconvesion of nitrile to acid insidethe cells of the coleoptileis discussed
7. The activities of 3-indolylacetamide and of 2:4-dichlorophenoxyaceticacid and the corresponding nitrile are considered in this connexion
8. The nitrile is destroyed by treatment with alkali but notbyacid. In the light of these results, it is desirable to re-examineprevious work on identification of auxins in plants by theiracid and alkali sensitivity. Evidence for the existence of thenitrile in a number of other plants is presented.

     

Effects of Applied Growth Regulators on Pod Growth and Seed Protein Composition in Pisum sativum L.

Plants of Pisum sativum L. raised from seed of an isogenic lineselected from cv. Greenfeast were grown under glasshouse conditions.The plant growth regulators naphthalene-acetic acid, benzyl-adenine,abscisic acid and gibberellic acid (GA₃) were administered todeveloping fruits by daily injections into the pedicels of podsbetween 2 d and 32 d after full bloom, thereby spanning thetime of maximum protein synthesis. Changes were observed ingrowth rates and dry weights of pods at maturity. Total proteincontent per cotyledon increased in naphthalene-acetic acid,benzyladenine and abscisic acid treatments. Legumin increasedin response to naphthalene-acetic acid and benzyladenine whilevicilin increased in response to abscisic acid. The albumincontent was not affected. Gibberellic acid (GA₃) caused no changesin total protein content or in levels of individual proteinfractions. The level of legumin was further increased by applicationof a one to one mixture of naphthalene-acetic acid and benzyladenine;this treatment also resulted in a marked increase in the albuminfraction but a considerable decrease in vicilin content. Theresults imply that hormones play a role in regulating proteinsynthesis and accumulation in Pisum. Key words: Hormones, Seed, Protein, Composition     

EVIDENCE ON THE SITE OF ACTION OF GROWTH RETARDANTS

1. The ability of five growth retardants to inhibit the GA-inducedand endogenous growth of Avena leaf sections has been investigated.The retardants vary in effectiveness. The order, from most effectiveto least, is Phosfon D, Amo-1618, C011, CCC and B995. 2. The inhibition of growth caused by Phosfon D and Amo-1618is not reversed by GA. It is apparent that the retardants donot compete with GA at the site of GA-action. 3. Addition of IAA will partially reverse the inhibition inducedby Phosfon D or Amo-1618. It is concluded that the retardantsact in part in Avena leaf sections by interfering with the auxinmetabolism of the tisssue. ¹ Supported in part by grants G-14578 and GB-1950 from the NationalScience Foundation ² Present address: Department of Botany, University of Washington,Seattle, Washington     

Effect of Growth Regulators and Light on Pollen Germination and Pollen Tube Growth in Pinus roxburghii Sarg

Pine (Pinus roxburghii) pollen grown in suspension cultureswas used to study the effects of growth regulators and lightconditions on germination and pollen tube growth. Indol-3-ylacetic acid, gibberellic acid, ethylene, abscisic acid and cyclicAMP (cAMP) at low concentrations (1–10 mg 1^–1) promotedgermination and tube growth. Addition of 1 and 10 mg 1^–1cAMP to any of the growth regulators had a promotory effect.Pollen tube growth decreased in white light as compared to thedark, and was increased in red light. Far-red light counteractedthe effect of red light. The effect of growth regulators incausing the enhanced tube growth appears to be manifested throughsubstances such as cAMP, and phytochrome seems to be involved. Pinus roxburghii, pine, pollen germination, pollen tube growth, growth regulators, cyclic AMP, phytochrome     

Development of Lipid Synthesis from CO2 in Avena Leaves during Greening of Etiolated Seedlings

The development of the lipid synthesizing system in Avena leafsections was examined in connection with carbon fixation duringthe greening of etiolated seedlings under light. During theinitial 2 h illumination there was a low level of CO₂ fixationby PEP carboxylation, but its products, malate and citrate,did not serve as a carbon source for lipid synthesis, althoughlipid synthesis from acetate had already been established. Withthe initiation of Calvin cycle activity after the initial 2h illumination, lipid synthesis began, with CO₂ fixed by RuBPcarboxylation serving exclusively as the carbon source. Fattyacid synthesis in the leaves during the initial 3 h illumination,unlike the fatty acid synthesis thereafter, was insensitiveto thiolactomycin, an inhibitor of type II fatty acid synthetasecontained in the plastids, and was not dependent on light, incontrast to light-dependent activity in greened leaves. The distribution of ¹⁴C incorporated into lipid molecules fromNaH¹⁴CO₃ showed an equal ratio of ¹⁴C in fatty acid, glyceroland choline moieties of labeled phosphatidylcholine, but a denserradioactivity in the galactose moiety than in the residual moietyof mono- and di-galactosyldiacylglycerols. This suggests a regulatedsupply of glycerol, choline and fatty acid moieties for phosphatidylcholinesynthesis, and an excess supply of galactose to diacylglycerolmoiety for galactosyldiacylglycerol synthesis in Avena leaves. (Received October 31, 1984; Accepted January 25, 1985)     

The Physio1ogical Activity of 2 : 6-Substituted Phenoxyacetic Acids

Anumber of 2 : 6-substituted phenoxyacetic acids in which theside chain had been substituted by ailcyl groups to form -propionic,-n-butyric and -n-valeric acids were investigated to assesstheir ability to act as growth-regulators. Besides employingstandard tedmiques of bioassay, further experiments were undertaken to determine the effects of these compounds on the vegetativegrowth and development of intact plants of Helianthus annuus. It has been established that all the compounds tested inducedcurvature in the Went pea curvature test and that without exceptionthe activity of the parent phenoxyacetic acid (2:6-dichloro-,2:4:6-trichloro-,2:6-dimethyl-, and 2:4-dichloro-6-methyl-)was increased by side chain substitution. In the Avena straight growth assay, the a 2:6-dichloro- and2:6-dimethyl- phenoxypropionic and butyric acids brought aboutstatistically significant increases in length of the coleoptilesections, when measurements were made at the end of 24 hours.Their activity was of the same order as that exhibited by a2:4-dichlorophenoxyacetic acid. Investigations were carried out on the uptake of water by sectionsof pea internode and the extension growth of Avena coleoptileaectiona when both the concentration and the length of treatmentwere varied. For some compounds it was found that over a certainrange of concentration water uptake and extension growth wereaccelerated in the initial 6–8 hours. Subsequent to this,inhibition occurred so that no significant increases above controlvalues were apparent at the end of 24 hours, and in some casesan actual loss of water or shrinkage in length took place. Itwas thus possible to demonstrate that 2:6-dimethylphenoxyaceticacid acts as a growth regulator in pea extension growth andthat 2:6-dichiorophenoxyacetic acid is active in the Avena test. The changes in the leaf area of individual pairs of leaves,together with the lengths of the internodes and shoot weightwere followed after application of measured amounts of eachcompound to the first pair of leaves of H. annuus. A numberof the 2:6-compounds were capable of modifying growth in wayssimilar to 2:4-dichlorophenoxyacetlc acid. However, much higherconcentration had to be applied in order to produce effectscomparable to those caused by the 2:4-dichloro- compound. Measurementsof the percentage of applied compound which penetrated intothe leaf showed that there were no marked differences in thisrespect between the different phenoxy acids. On the other hand,experiments in which the treated leaves were left on the plantfor varying periods of time led to the conclusion that the a: 6-substituted compounds are less readily translocated than2:4-dichlorophenoxyacetic acid.     

Physiological activity of a viridicatin derivative, 3-(4-phenylcarbostyriloxy) acetic acid

A carboxymethylene derivative (V-OCH₂COOH) of viridicatin (V-OH)promoted the root growth of rice and sesame seedlings. V-OCH₂COOHhad no known hormonal activities, per se, but did have an inhibitoryeffect on IAA and 2,4-D-induced growth of Avena coleoptile sectionsand of carrot root callus. However, inhibition by VOCH2COOHof 2,4-D-induced growth in carrot root callus was to some extentreversed by increasing the concentration of 2,4-D. V-OCH₂C0OHseemed to competitively inhibit IAA-induced elongation of Avenacoleoptile sections. (Received September 14, 1970; )     

Steroidal Saponins are not Main Building Units of the Prolamellar Body in Etioplasts

Sugar-containing lipids were analyzed by thin layer chromatographyin various cell fractions of etiolated Aoena leaves, Auena intactetioplasts and prolamellar bodies isolated from Cucurbita etioplasts.We confirmed the presence of steroidal saponins, avenacosidesA and B in etiolated leaves and crude etioplast fraction ofAvena, but scarcely detected them in Avena intact etioplastspurified by Percoll density gradient centrifugation. Saponinswere hardly detected in the paracrystalline prolamellar bodiesfrom Cucurbita etioplasts. We concluded that steroidal saponinsare not main building units of the prolamellar body in the etioplasts. (Received August 5, 1982; Accepted February 15, 1983)     

Adventitious Bud Formation from Mature Embryos of Picea chihuahuana Martinez, an Endangered Mexican Spruce Tree

Zygotic embryos of Picea chihuahuana Martínez were cultivatedin vitro to determine the time of organogenic competence andto maximize adventitious bud induction. The induction mediumconsisted of modified B5 substrate supplemented with N⁶-benzyladenine(with or without naphthalene acetic acid) or kinetin (with orwithout 2-4, dichlorophenoxyacetic acid) at different concentrationsand induction times. The minimum induction time required forbud formation was 14 d with kinetin and 17 d with N⁶-benzyladenine.After induction embryos were transferred to the proliferationmedium (modified B5 substrate with 50% of its components andwithout growth regulators) for 30 d. The subsequent buds weretransferred every 15 d to Schenk and Hildebrandt medium at halfits concentration without growth regulators. The most effectivetreatments were 3 and 5 mg l^-1kinetin or N⁶-benzyladenine whichproduced five to seven buds per embryo. The largest shoots weresubjected to rooting trials with pulses of different concentrationsof indole butyric acid resulting in only one bud developinga root. Histological analysis revealed clusters of three tofour cells that became more evident as induction time increased.Kinetin promoted the development of an organized structure priorto adventitious buds formation sooner than N⁶-benzyladenine.Copyright 2000 Annals of Botany Company Competence, plant tissue culture, micropropagation, Picea chihuahuana, endangered species, spruce     

Repetitive DNA, Genome and Species Relationships in Avena and Arrhenatherum(Poaceae)

Repetitive sequences have been widely used for examining genomeand species relationships by in situ and Southern hybridization.In the present study, double-stranded DNA sequences, from denaturedDNA reannealed to Cot = 1, from Avena strigosa(2 n = 2x = 14;A genome; referred to as CotA) and Avena sativa(2n = 6 x =42; ACD genome; referred to as CotACD) were isolated with ahydroxyapatite column, and were used for in situ hybridizationon hexaploid A. sativa chromosomes. Probe CotACD labelled allchromosomes evenly throughout their length at the same intensity.Probe CotA labelled the 28 A and D genome chromosomes stronglyand the 14 C genome chromosomes weakly. Three cloned repetitivesequences, pAvKB9 (126 bp), pAvKB26 (223 bp) and pAvKB32 (721bp) were characterized in the A, B, C and D Avena genomes andthe genus Arrhenatherum using molecular and cytological methods.Clones pAvKB9 and pAvKB26 were absent from the Avena C genome,while both could identify the presence of the D genome by Southernhybridization. In situ hybridization to diploid and tetraploidAvena species revealed that the probes showed a dispersed genomicorganization and that they are present on both arms of all chromosomes.These sequences were excluded from areas where tandem repeats,such as rRNA genes and telomeres, are present. These resultsindicate the close relationship between A and D genomes andthe presence of common DNA sequences between A and C Avena genomes.All three clones hybridized to Southern blots containingArrhenatherumdigested genomic DNA, indicating Arrhenatherum’s closeaffinity to A, B and D Avena genomes. Copyright 2000 Annalsof Botany Company Cereals, DNA, hydroxyapatite, in situ hybridization, oats, reassociation kinetics, repetitive DNA     

The Relationship between the Growth of the Primary Leaf and of the Coleoptile in Seedlings of Avena and Triticum

Partial inhibition of extension growth of the primary leaf occurswhen whole Triticum seedlings are immersed in aerated solutionsof IAA but is replaced by growth promotion when sucrose is addedto the external solution. In seedlings in which the coleoptilehas been excised, IAA increases the growth of the leaf bothwith and without additional sucrose. Inhibition of the leaf by moderate concentrations of IAA nolonger occurs when the seedling is detached from the endosperm.Sucrose added to the external solution raised the percentageelongation of the coleoptile almost to the level of that attainedin intact seedlings without additional carbohydrate. It alsoenabled the leaf to show a positive growth response with IAA. The results indicate that in intact seedlings treated with IAAthe growth of the primary leaf is markedly diminished owingto diversion of carbohydrate to the coleoptile if the growthof the latter is promoted as a result of the treatment. Whenthe competition of the coleoptile for carbohydrate is diminishedor eliminated, acceleration of the growth of the primary leafby IAA becomes apparent. In addition to the endogenous rhythm, with a period close to24 hours, induced in the growth-rate of the coleoptile whenseedlings of Avena are transferred from red light to darkness,a similar rhythm, with a slightly longer period, is inducedin the growth-rate of the primary leaf. This rhythm persistsin elongating leaves so long as they remain within the coleoptile.It can be recorded for at least 100 hours in deseeded seedlings. When intact seedlings of Avena are immersed for one hour inrelatively high concentrations of IAA and then transferred todistilled water for 18 hours, the elongation of the coleoptileis greater and the inhibition of the leaf is less than whenthey are transferred to humid air. Sections of the leaf of Triticum showed a slight increase inelongation in concentrations of IAA up to 5 mg./l., but no evidencewas obtained that sections of leaf and coleoptile exert any.influenceon each other's elongation when floated together on solutionsof IAA.