Studies on Extension Growth in Coleoptile Sections: I. The Influence of Age of Coleoptile upon the Response of Sections of IAA

One of the problems involved in carrying out large-scale coleoptilecylinder straight growth assays is the effect of coleoptileage upon the behaviour of the sections. This effect, as measuredboth by the length of coleoptile and the time from sowing theseeds, has been investigated by an examination of the growthof sections cut from coleoptiles of several length grades onfive occasions 6–10 hours apart. The response of thesesections to a range of concentrations of ß-indolylaceticacid (IAA) was followed during the period of growth to ascertainthe most suitable time for measurement of sections in a routinetest. A number of general trends associated with coleoptile age (whethermeasured by length, or time from planting) were observed inamount of growth, growth-rate, period of growth, and sensitivity.It is suggested that these characteristics are associated withthe amount of the total growth already made by the parent coleoptileat the time of taking the section, and also that the sectionexhibits an ‘intrinsic growth-rate’ related to thegrowth-rate of the coleoptile at the time the section is cut. A period of growth of 17–20 hours seems satisfactory forroutine tests except where very young coleoptiles are used;in this case growth less than that in water is sometimes observedin very low concentrations of IAA.     

Studies in the Physiology of the Onion Plant: V. AN INVESTIGATION INTO THE GROWTH SUBSTANCE CONTENT OF BULBING ONIONS

Extracts have been prepared from induced and non-induced onionplants. These extracts have been fractionated and the ether-soluble,acidic components investigated using the wheat coleoptile straight-growthassay, colorimetric determination of 3-indolylacetic acid (IAA),and a new bioassay which has been introduced and modified togive reproducible results. This last is an assay of substanceswhich will cause ‘bulbing’ (swelling of the leafbases) of onion plants, and it has been used to demonstratea number of factors which influence the initiation of bulbingin the onion. It has been shown that substances are presentin extracts of onion tissue which will cause an increase inthe ‘bulbing ratio’ of test onion seedling sections. Results indicate that there is an increase in the IAA contentto a very high level during the first week following induction—beforethere is any visible sign of swelling of the leaf bases—butthat this falls off rapidly after 5–7 days and eventuallyfalls below the level found in non-induced plants.     

Factors Affecting the Abscission of Reproductive Organs in Yellow Lupins (Lupinus luteus L.): III. ENDOGENOUS GROWTH SUBSTANCES IN VIRUS-INFECTED AND HEALTHY PLANTS AND THEIR EFFECT ON ABSCISSION

Extracts of small and mature-size lupin pods yielded four substancesaffecting the growth of wheat-coleoptile sections: one acidpromotor (A), two acid inhibitors(B and X), and one neutralinhibitor(Y). Inhibitor B was extremely active, however, coleoptile sectionsshowed no signs of toxic effects; they resumed growth at a rapidrate after rinsing them and adding ß-indolylaceticand (IAA) to the medium. 1 µg of IAA was required to counteractthe effect of ‘B’ extracted from 230 mg. Of tissue.On an equal fresh weight basis the inhibiting action of ‘B’in lupin pods was 500–1,500 times more potent than thatof ‘inhibitor ß’ in etiolated pea seedlings. Small pods of plants infected with pea-mosaic virus yielded3 times the amount of ‘A’ of healthy plants (equivalentto 1 µg. IAA 0.3 µg. IAA per 25 g. of tissue respectively),and approximately the amount of ‘B’. Mature podsof virus-infected plants again yielded more‘A’,but also 2? times more ‘B’ than pods of healthyplants. Healthy pods yielded more ‘A’ than virus-infectedpods, and there was no difference in ‘X’. A lupin abscission test was developed and the effects of proximaland distal application of -naphthyl acetic acid (NAA) are presented,and discussed with respect to results of other abscission tests. ‘A’ accelerated abscission when applied proximally,and delayed or prevented it when applied distally. ‘B’strongly accelerated abscission when applied in either way.A possible mechanism explaining the abscission-inducing effectof developing pods on later flowers is discussed in terms ofthe substances ‘A’ and ‘B’. The partlyprevented abscission observed on virus-infected plants was foundto agree well with the proposed mechanism.     

The Growth Substances separated from Plant Extracts by Chromatography: II. THE COLEOPTILE AND ROOT ELONGATION PROPERTIES OF THE GROWTH SUBSTANCES IN PLANT EXTRACTS

1. 1. A method for the running of ‘strip’ chromatogramsof plant extracts, as large-scale sources of the naturally occurringgrowth substances accelerator () and inhibitor ß(ß), and the elution of these substances togetherwith indole-3-acetic acid (IAA), is described. A method is givenfor the testing of the pea root section extension propertiesof these growth substances.
2. 2. Coleoptile and root sectionextension tests over a completeconcentration range are donefor , ß, and eluted IAA,and mixtures of and ßwith IAA or indole-3-acetonitrile(IAN) are tested for coleoptilesection extension.
3. 3. promotes at low concentrations andinhibits at high concentrationsboth coleoptile and root sectionextension and the coleoptilesection extension induced by IAAor IAN. ß inhibitscoleoptile and root section extensionover the whole concentrationrange; it also inhibits IAA andIAN induced coleoptile sectionextension.
4. 4. The extensionof coleoptile sections in mixtures of or ßwith IAAis measured at a number of time intervals. , aloneand withIAA, has its greatest promoting effect in the earlystages andits greatest inhibiting effect in the later stagesof sectiongrowth. ß, alone, promotes the early stagesand inhibitsthe later stages of section growth and, with IAA,has its greatestinhibitory effects in the later stages.

     

Chelation in Auxin Action: I. A STUDY OF THE INTERACTIONS OF 3-INDOLYLACETIC ACID AND SYNTHETIC CHELATING AGENTS AS AFFECTING THE GROWTH OF WHEAT ROOTS AND COLEOPTILE SECTIONS

Factorial experiments have been carried out on the effects,upon growth of roots of intact wheat seedlings and growth ofwheat coleoptile sections, of different concentrations of 3-indolylaceticacid (IAA) and various known chelating agents. These have demonstrateda similar mutual antagonism between pairs of agents whetherthese are IAA and a single known chelating agent or two knownchelating agents. This interaction takes the form that eitheragent alone in ‘high’ concentration severely inhibitsgrowth but this inhibitory effect is almost or entirely removedby the presence of one-millionth the concentration of the otheragent; when both agents are present in ‘high’ concentrationthe inhibition is again severe. The substitution of a non-chelatinganalogue for one of the agents either destroys the mutual characterof the antagonism or entirely prevents either agent at low concentrationfrom reducing measurably the inhibition caused by high concentrationof the other. The fact that IAA interacts with known chelatingagents, in controlling the growth both of roots and coleoptilesections, in the same unexpected and symmetrical way that theseinteract with each other, is held strongly to support the hypothesisthat it is here itself acting as a chelating or complexing agent;the absence of such interactions with a non-chelating analoguemakes this the more convincing. These results are concernedwith the removal of growth inhibition, due to supra-optimalconcentrations of one agent, by minute proportions of another;it cannot be regarded as proven that the promotion of growthby IAA in the absence of another agent is also due to chelationor complex formation. This seems probable, however, when thefindings here presented are taken in conjunction with the accumulatingevidence that IAA and other auxins can form complexes or chelateswith metals in vitro, and with the finding already publishedin detail that the eight chelating agents tried promoted growthin the wheat coleoptile test. The main criticisms to which this hypothesis has been subjectedhave been concerned with the relative magnitudes of effectsof IAA and chelating agents upon growth, with the low stabilityconstants of metal complexes with IAA and other auxins, withthe lack of parallelism between stability constants and growth-promotingactivity, and with the fact that one chelating agent (ethylenediamine-tetraaceticacid; EDTA) has been found inactive in certain growth tests.A series of factorial experiments comparing the authors' techniques(which are here described in detail), chemicals, and strainof wheat with those used by Fawcett et al. (1956) demonstratethat the discrepancies found, both as regards magnitudes ofeffects of IAA and EDTA and optimal concentrations, were partlydue to differences in strain but mainly to differences of technique.It is considered that ‘foreign’ molecules such asEDTA are likely to have side effects, which may well differin different strains or tests; competition with internal chelators(Burstrom and Tullin, 1957) is also likely to differ; differencesin rate of penetration and steric hindrance may also be involved.For these reasons effective chelating activity in vivo may bevery different from that in vitro and in the first instancethe magnitudes of growth-promoting effects of chelating agents(which may indeed be the net result of stimulatory and inhibitoryprocesses) seem less important than the fact that they are foundin so many instances. Possible ways in which IAA and other growth substances may regulategrowth by chelation or complex-formation are discussed.     

IAA Amino Acid Conjugates Induce Differentiation of Tracheary Strands in Lettuce Pith Explants

Each of four amino acid conjugates of IAA was able to replacethe IAA requirement for xylogenesis in lettuce pith explants,when supplied at concentrations ten to 100 times those optimalfor IAA. Tracheary development induced by these conjugates tendedto be slightly slower and less in amount than with IAA, andthe tracheary strands shorter and less regular. Responses differedsomewhat among the four conjugates: IAA-D, L-aspartate gavedevelopment most like that with free IAA, and IAA-D, L-phenylalanineoften yielded the weakest tracheary development, while responsesto IAA-L-alanine and IAA-glycine were intermediate. The resultsare interpreted in terms of the ‘bound’ IAA conjugatesdiffusing into the pith explants and becoming xylogenic onlyon hydrolysis to ‘free’ IAA. As tracheary strandformation is believed to result from IAA fluxes, it seems thatthe free IAA also moved through the discs, presumably towardsthe surfaces where it degrades rapidly. Tracheary strand formationin these explants can be compared with vascular strand formationin the normal shoot tip, where IAA conjugates (auxin ‘precursors’)move acropetally and are hydrolysed to free IAA especially inthe young leaf primordia, we suggest, yielding local sourcesof IAA which may contribute both to the phyllotactic spacingof primordia and, moving basipetally, to the definition of theauxin pathways that develop as procambial strands behind individualleaf primordia. Lactuca sativa, lettuce, IAA conjugates, tracheary element differentiation, pith explants, xylem strands     

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.     

Effects of Flooding and Drainage and their Alternation on the Growth and Uptake of Nutrients by Rice (Oryza sativa L., indica, var. IR-8)

Continuous flooding of the soil (‘flooded’ treatment)gave best growth of IR-8 variety of rice whereas soil drainedfor 4 weeks and then flooded for 8 (‘drained and flooded’treatment) resulted in poorest growth and chlorotic plants.Plants grown in the continuously drained soil (‘drained’treatment) and those in the soil flooded for 4 weeks and thendrained for 8 (‘flooded and drained’ treatment)showed intermediate growth. There were no differences in therelative water content of plants growing in the various treatments.Analyses of plant tissues showed that a consideration of therelative concentration of Fe, Mn, and P in the shoots is mostclosely related to the performance of rice under various culturalconditions. An increase in the concentration of Fe in the planttissues following flooding was correlated with the best growth(‘flooded’ treatment) unless it was accompaniedby high level of Mn (as in the ‘drained and flooded’treatment) which may have proved toxic, e.g. by interferencewith Fe metabolism as was evidenced by chlorosis. Measurementsof oxidation-reduction potentials, oxygen diffusion rates, andthe concentration of exchangeable and soluble Fe and Mn in thesoils have shown that the ‘drained and flooded’treatment caused the most extreme reducing conditions. Floodingaccompanied by the development of extreme reducing conditionsled to a greater accumulation of Mn in the shoots (‘drainedand flooded’ treatment) whereas flooding accompanied bythe maintenance of oxidizing conditions (‘flooded’treatment) resulted in a lower uptake of Mn. Growth of riceplants for 4 weeks in the drained soil did not fit them forthe reduced conditions which developed during subsequent flooding(‘drained and flooded’ treatment).     

Effects of 2-Chloroethylphosphonic Acid on Growth, Plastid Pigments, and Sucrose Translocation in Radish

2-Chloroethylphosphonic acid (CEPA) caused a significant declinein chlorophyll content of radish plant within 5 d of treatment.Such effects were greater when plants were treated at the two-than at the four-leaf stage. In early treated plants, concentrationof CEPA increasing from 20 mg/1 progressively increased leafweight, while decreasing root (radish) weight. A concentrationof 10 mg/1, applied at the three-leaf stage, increased leafand root weights by 27 and 30 per cent respectively in the cultivar‘Cavalier’. Similar responses were obtained withthe cultivar ‘Cherry Belle’. While Cavalier showeda discrete 10 mg/1 optimum, ‘Cherry Belle’ exhibiteda range of concentrations (10-40 mg/1) optimal for growth. At relatively high concentrations, early application of CEPAcaused inverse changes in sucrose-¹⁴C in the leaves and theroot, so that decreased retention by leaves was accompaniedby increased transport to roots. Low concentrations of CEPAappear promising for growth stimulation in root-crop plants.     

Epidermal Growth Factor Interacts with Indole-3-Acetic Acid and Promotes Coleoptile Growth

We used coleoptile sections of Avena sativa, Sorghum bicolor,and Zea mays seedlings to examine interactions between epidermalgrowth factor (EGF) and indole-3-acetic acid (IAA) that mayaffect plant growth and development. Our 24-h bioassays employedthree controls ranging in dilution from 10^–4 to 10^–8g ml^–1: (1) 50 mM potassium-phosphate buffer solution(pH=6.0), (2) bovine serum albumin, a nonspecific protein; and(3) IAA; plus two treatments: (1) mouse epidermal growth factor(EGF) ranging from 10^–6 to 10^–10gml^–1, and(2) EGF + IAA. In all three species growth in IAA, EGF, andEGF + IAA treatments showed significant increases over controls;EGF+IAA showed significant increases in growth over IAA alone.As the concentrations of IAA decreased, the EGF and IAA interactionbecame more pronounced. At the highest IAA concentrations, EGF+ IAA increased growth rates ca. 2% to 39%, whereas at lowerIAA concentrations EGF + IAA promoted growth as much as 121%,thereby lowering the normal IAA physiological set point up tothree or four orders of magnitude. Our data suggest that aninteraction between EGF and IAA may allow plants to recognizeand respond to animal biochemical messengers, resulting in changesin plant cell elongation that ultimately may alter plant growthpatterns. (Received April 27, 1994; Accepted September 5, 1994)     

The Metabolism of 3-Indolylacetic Acid in Plant Tissues3

The nature of metabolic products of 3–indolylacetic acid(IAA) extracted from potato tuber disks treated with aeratedIAA solution has been investigated. Two major products, knownat first as ‘V’ and ‘P’ in these studieshave been isolated and ‘V’ has been identified as3-indolylacetylaspartic acid (IacAsp). The rapid uptake of IAA is inhibitited by metabolic poisonssuch as 10^–3 M. cyanide. The maximum mean internal concentrationexceeds the external concentration well–aerated cultures.The mean internal concentration, however only remains for aperiod and then falls off rapidly as a result of extrusion ofabsorbed IAA into the external solution. This extrusion is notinhibited by 10^-3 cyanide; when the mean internal IAA concentrationis 150 µ mol/ml. and the localized IAA concentration musttherefore exceed this value. We conclude therefore that theIAA concentration in the sites where it has accumulated exceedsthe concentration of IAA outside. Uptake of IAA and also its further conversion are inhibitedby indolylacetonitrile and promoted by aspartate, but this promotionis not associated with any gain in amount of indolylacetylaspartate(IacAsp). The data suggest that IacAsp may be formed in tissue from ‘boundIAA’ rather then free IAA. The ‘accelerator ’ found in potato and beans whichhas similar R_F to IAcAsp has been shown definity to be someother substance or substances and not IAcAsp as was at firstthought possible.     

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).     

Anoxia tolerance in rice seedlings: exogenous glucose improves growth of an anoxia-'intolerant', but not of a 'tolerant' genotype

This study demonstrated that, in rice seedlings, genotypic differencein tolerance to anoxia only occurred when anoxia was imposedat imbibition, but not at 3 d after imbibition. When seeds wereimbibed and grown in anoxia, IR22 (anoxia-‘intolerant’)grew much slower and had lower soluble sugar concentrationsin coleoptiles and seeds than Amaroo (anoxia-‘tolerant’),while Calrose was intermediate. After 3 d in anoxia, the sugarconcentrations in embryos and endosperms of anoxic seedlingswere nearly 4-fold lower in IR22 than in Amaroo. Sugar deficitin the embryo of IR22 is presumably due to the limitation ofsugar mobilization rather than the capacity of transport asshown by similar sugar accumulation ratios of 1.8 between embryoand endosperm in IR22 and Amaroo at 3 d in anoxia. With 20 molm^–3 exogenous glucose, coleoptile extension and freshweight increments in anoxic seedlings of IR22 were much closerto those in the two other genotypes, nevertheless protein concentrationremained lowest on a fresh weight basis in the coleoptiles ofIR22; indicating that protein synthesis has a lower priorityfor energy apportionment during anoxia than processes crucialto coleoptile extension. In contrast to these responses to anoxiaimposed at imbibition, IR22 had nearly the same high toleranceto anoxia as Calrose and Amaroo, when anoxia was imposed onseedlings subsequent to 48 h aeration followed by 16 h hypoxicpretreatment. In fact, coleoptiles of anoxic IR22 had highersugar concentrations and grew faster than Calrose, and exogenousglucose had no effect on the coleoptile extension of IR22. Excisedcoleoptile tips of IR22 and Amaroo with exogenous glucose hadsimilar rates of ethanol production and were equally tolerantto anoxia. In conclusion, much of the anoxia ‘intolerance’of IR22 when germinated in anoxia could be attributed to limitedsubstrate availability to the embryo and coleoptile, presumablydue to slow starch hydrolysis in the endosperm. Key words: Anoxia, coleoptile, embryo, endosperm, ethanol production, germination, growth, Oryza sativa L., solute net uptake or loss, sugar availability.     

Studies on the Geotropism of Roots: III. EFFECTS OF GEOTROPIC STIMULATION ON GROWTH-SUBSTANCE CONCENTRATIONS IN VICIA FABA ROOT TIPS

The auxins contained in 5-mm. tips of horizontal Vicia fabaroots have been compared with those in tips of vertical rootsafter cold ethanol extraction, paper-chromatographic separation,and Avena mesocotyl bioassay. At about the time curvature commencesin horizontal roots there is a marked increase in the contentof an auxin corresponding to ‘AP(ii)’ of pea roots(Rf 0.35–0.65 in isobutanol/methanol/water). There areindications that this is not due to its release from an inactivebound state but that it is either synthesized de novo or maybe converted from another auxin corresponding to ‘AP(iii)’of pea roots (Rf 0.75–1.0). The literature dealing with the auxins of geotropically stimulatedorgans is reassessed and it is concluded that, with the exceptionof the Avena coleoptile, there is very little evidence favouringa simple transport redistribution of auxin under gravity; themajority of the data favour an effect of gravity on auxin metabolism.     

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.     

The Effects of Indole-3-Acetic Acid and 2:4-Dichlorophenoxyacetic Acid on the Growth Rate and Endogenous Rhythm of Intact AvenaColeoptiles

The rates of elongation of the coleoptiles of Avena seedlings,subjected to intermittent immersion in solutions of IAA or 2:4-Dfor various total periods, were determined from measurementsof photographs taken every hour by infra-red radiation. Immersion in 17·5 mg./l. IAA for 1–5 hours causeda large increase in the growth rate followed by a depression.When the seedlings were immersed in 8·75 mg./l. IAA forperiods of 12 or 24 hours the depression was partially overcomeso long as the treatment was continued. Absorption of additionalIAA by the coleoptiles reduced their geotropic sensitivity. Penetration of 2:4-D (sodium salt) into the coleoptiles wasslower than that of IAA and the resulting stimulation of thegrowth rate was less, particularly in unbuffered solutions.After the treatment the growth rate declined slowly to aboutthe normal value. Results with coleoptiles were very similar to those previouslyobtained with rhizomes of Aegopodium and suggest that inhibitionof growth following stimulation by IAA may be of general occurrence.Possible causes of the inhibition are discussed and a comparisonis made between the results with intact coleoptiles and observationsmade by others on coleoptile sections. Temporary immersion of the seedlings in auxin solutions depressedthe rate of elongation of the primary leaf while it increasedthat of the coleoptile. It caused little disturbance of theendogenous rhythm induced by change from light to darkness.The suggestion that such rhythms can be explained in terms ofvariation in concentration of IAA-oxidase is not supported.     

The Growth Substances separated from Plant Extracts by Chromatography. I

Methods for the chromatographic separation on paper of indolecompounds and for the direct biological assay of the chrornatograinsusing the Avena coleoptile straight-growth method are described.Reagents for the detection of the indole-3-carboxylic acids,indole-3-acetonitrile, and gramirte as coloured spots on chromatogramsare compared and the areas of such spots are shown to be proportionalto the logarithms of the quantities of substance present. The procedure of chromatography described is shown not to involvea loss of indole-3-acetic acid activity if chromatography isdone in darkness and chrornatograms are not stored in lightand air. Methods are described for the extraction of growth aubstancesfrom plant materials, the purification and chromatography, onpaper, of the extracts and the bioassay of the chromatogramsusing Avena coleoptile sections. The ether extracts, containing acidic substances, of etiolatedbroad bean and pea shoots and roots, etiolated sunflower shoots,maize roots, and potato etiolated shoots and tuber have beenchromatographed and the chromatograms bioassayed. On all chromatogramsthree areas active in Avena coleoptile section growth are found.One area of growth promotion is shown due to indole-3-aceticacid [IAA]. Another area of growth promotion and, one of growthinhibition are due to unknown substances, which are named accelerator () and inhibitor ß (ß) respectively. On chromatograms of potato tuber a fourth growth-promoting area,in addition to those described above, is detected and is shownto be probably due to indole-3-acetonitrile [IAN]. IAN or indole-3-pyruvicacid may occpr together with IAA on chrormatograms of extractsof immature maize kernels and cauliflower head respectively. On cabbage extract chromatograms the growth-promoting activitycorresponding in position with IAA is shown to be due to IAAand to IAA alone. In etiolated broad bean shoots IAA is the predominating growthsubstance in the stem and ß predominates in the firstlateral bud. The latter is suggested as an explanation of apicaldominance, and the predominance of ß in potato tuberskin is suggested as an explanation of dormancy in tubers. In the broad bean root the acidic growth-substance patterns,for the whole root and for the sections 0–2 cm. and 2–4cm. from the tip, are the same. The acidic growth substances extractable from broad bean shootsare the same whether the plant material is boiled or frozenbefore extraction.     

Effects of the steroidal alkaloid tomatine in auxin bioassays and its interaction with indole-3-acetic acid

Summary The steroidal alkaloid tomatine did not enhance elongation of oat coleoptile and first internode sections, or of wheat coleoptile sections. Higher concentrations of the alkaloid inhibited elongation and interacted antagonistically with IAA. Although 10^-4 M tomatine alone did not influence elongation of oat coleoptile sections, it did reduce growth response to exogenous IAA. Tomatine concentrations less than 10^-4 M did not influence response to IAA. The auxin activity of tomatine, reported by Vendrig, was therefore not confirmed.     

The Galls on Forsythia intermedia Zab.

The galls on Forsythia intermedia Zab. consist of much-branched,root-like structures embedded in corky material which appearsto be sloughed-off from them. These gall ‘roots’have 7 to 14 vascular bundles compared with the 5 of normalroots and contain much more IAA. When galls were incubated in damp chambers the gall ‘roots’extended their growth. These extensions had a root-cap and root-hairsbut also had more vascular bundles than normal and they didnot respond geotropically like normal roots. Two fungi, Gibberella baccata (Wallr.) Sacc. (conid, stat. Fusarlumlateritium Nees.) and Phomopsis dominici Trav. were associatedwith die-back of gall ‘roots’ and two bacteria resemblingCorynebacterium fascians (Til.) Dowson and Agrobacterium tumefaciens(Sm. and Towns.) Conn respectively were isolated from galls.All produced IAA in culture media but their role in the etiologyof the gall, if any, remains in doubt.     

The Effect of Applied Growth Hormones on Cambial Division and the Differentiation of the Cambial Derivatives

When indole-3-acetic acid (IAA) is applied to woody shoots cambialdivision is stimulated and the cambial derivatives differentiateto produce xylem tissue. When gibberellic acid (GA) is applied,cambial division occurs but the resultant derivatives on thexylem side of the cambium remain undifferentiated. The relativelevels of applied IAA and GA are important in determining whethermainly xylem or phloem tissue is produced. High IAA/low GA concentrationsfavour xylem formation, whereas low IAA/high GA concentrationsfavour phloem production. The new phloem tissue produced asa result of hormone treatment is fully differentiated, containingsieve elements and sieve plates. IAA is important in promotingthe elongation of the cambial derivatives to produce xylem vesseland fibre elements, though in the case of xylem fibres appliedGA causes further elongation. IAA is an important factor indetermining vessel diameter in the ring-porous species Robiniapseudacacia, high levels of applied IAA giving wide springwood-typevessels and low levels giving narrow ‘summerwood’vessels.