THE RELATIONSHIP OF GIBBERELLIN AND AUXIN IN PLANT GROWTH

No synergism was found between IAA and gibberellin in the Avenucurvature test and this bioassay thus measures changes in diffusibleauxin resulting from gibberellin treatment and not a synergisticaction of the gibberellin on the curvature response to auxin.Gibberellin treatment causes an increase in diffusible auxinfrom the stem apex of dwarf pea (Pisum sativum L. var. LittleMarvel) 24 to 48 hours before the elongation response in thestem. The increase in diffusible auxin in the stem apex of Centaureacyanus L. var. Blue Boy occurs four to six days before the boltingresponse to gibberellin treatment under short days. The stemtissues of both the dwarf pea and Centaurea show an elongationresponse to IAA when the IAA is applied in a manner simulatingthe stem apex. Thus the growth of the dwarf pea and the boltingof Centaurea brought about by treatment with gibberellin aredependent on an increase in diffusible auxin. ¹Present address: Biological Institute, College of General Education,University of Tokyo, Komaba, Meguro, Tokyo.     

Endogenous factors affecting the curved growth of seminal roots of Zea mays L. seedlings grown in liquid culture

Seminal roots of Zea mays L. show curved growth, i.e. waving,meandering and spiral growth, when water cultured. Root curvaturewas accelerated by exogenously applied indole-3-acetic acidat 10^–9 M and gibberellic acid at 10^–6M; this curvaturedisappeared when 10^–7 M p-chlorophenoxyisobutyric acidwas added. Roots curved more when the tops of seedlings wereexposed to light than when the tops of seedlings were covered.These results suggest that auxin may induce root curvature. (Received February 29, 1980; )     

The Effects of Oil-based Fungicides on Water Loss of Coleus blumei Leaves and Pelargonium Hybrid Petals

Effects of oil-based fungicides on plant surfaces were studiedby assessing water loss from excised sprayed leaves or petalsand by microscopy. Two fungicides (Turbair Zineb Fungicide andTurbair Copper Fungicide) were sprayed, using a Potter tower,onto the adaxial surfaces of excised leaves or petals, and weightloss was determined as a measure of water loss. Doses of approximately4–9 g m^–2 significantly increased water loss fromPelargonium hybrid petals and leaves of Coleus blumei Benth.The fungicides, their supernatants and the carrier oil increasedwater loss from the petals but effects of the supernatants andthe carrier oil on C. blumei leaves were less conclusive. LowTemperature Scanning Electron Microscopy (LTSEM) did not revealany scoring or marked erosion of the adaxial surface of leavesor petals 24 h after application of the fungicides. Coleus blumei Benth., Pelargonium hybrid, cuticle, fungicides, oils, LTSEM, water loss     

Calcium Involvement In the IAA-induced Leaflet Opening of Cassia fasciculata

Opening of Cassia fasciculata leaflets was induced in darknessafter application of indole-3-acetic acid (IAA). This movementwas obtained with concentrations from 10^–6 M to 10^–4M, after a corresponding time-lag ranging from 120 to 30 min.IAA (5x10^–5 M) allowed leaflet opening at all the pH valuestested (from 3·5 to 7·5), the largest aperturebeing obtained at pH 60 in MES 2·5 mM. Our data suggesta functional involvement of calcium in the regulation of theturgor variations occurring in the pulvinar motor cells duringIAA-induced leaflet opening which occurs in darkness: indeed,this movement was inhibited by the Ca²⁺ chelator EGTA (thisinhibition was reversed by CaCl²) or by antagonists (LaCl³,TMB-8); on the contrary, the IAA-opening was enhanced by ionophoreA 23187. Calcium mobilization through specific channels was tested usingantagonists such as verapamil and nifedipine: at physiologicaldoses, these compounds did not significantly affect leafletresponse. The possibility that calcium could originate frominternal stores was checked using lithium chloride which isknown to block the phosphatidylinositol cycle in animal cells.This compound hindered auxin-induced opening for concentrationshigher than 5x10^–4 M. The calcium-binding protein calmodulinwas shown to be implicated in the IAA-induced response sinceopening was inhibited in a concentration-dependent manner aftertreatment with compound 48/80 and with W-7. Key words: Cassia fasciculata, auxin, calcium, second messenger, turgor regulation     

Effects of Inhibitors of Protein Synthesis on Transmembrane Auxin Transport in Cucurbita pepo L. Hypocotyl Segments

Pretreatment of 2?0 mm segments of etiolated zucchini (Cucurbitapepo L.) hypocotyl with cycloheximide (CH) or 2-(4-methyl-2,6-dinitroanilino)-N-methylpropionamide(MDMP) eliminated the stimulation by N-1-naphthylphthalamicacid (NPA) of net uptake of [1-¹⁴C]indol-3yl-acetic acid ([1-¹⁴C]IAA),but had relatively little effect on the net uptake of IAA inthe absence of NPA. The efflux of [1-¹⁴C]IAA from preloadedsegments was not substantially affected by inhibitor pretreatmentin the absence of NPA, but CH pretreatment significantly inhibitedthe reduction of efflux caused by NPA. Pretreatment with CHor MDMP did not affect net uptake by segments of the pH probe[2-¹⁴C]5,5-dimethyl-oxazolidine-2,4-dione ([2-¹⁴C]DMO), or thenet uptake of [¹⁴C]-labelled 3-O-methylglucose ([¹⁴C]3-0-MeGlu),suggesting that neither inhibitor affected intracellular pHor the general function of proton symporters in the plasma membrane.Both compounds reduced the incorporation of label from [³⁵S]methionineinto trichloroacetic acid (TCA)-insoluble fractions of zucchinitissue, confirming their inhibitory effect on protein synthesis. The steady-state association of [³H]IAA with microsomal vesiclesprepared from zucchini hypocotyl tissue was enhanced by theinclusion of NPA in the uptake medium. The stimulation by NPAof [³H]IAA association with microsomes was substantially reducedwhen the tissue was pretreated with CH. However, CH pretreatmentdid not affect the level of high affinity NPA binding to themembranes indicating that treatments did not result in lossof NPA receptors. It is suggested that the auxin transport site on the effluxcarrier system and the receptor site for NPA may reside on separateproteins linked by a third, rapidly turned-over, transducingprotein. Key words: Auxin carriers, auxin efflux, Cucurbita pepo, phytotropin receptors     

Studies on the Geotropism of Roots: I.GROWTH-RATE DISTRIBUTION DURING RESPONSE AND THE EFFECTS OF APPLIED AUXINSI

Experiments are described in which the normal geotropic responsesof the roots of Pisum sativum seedlings have been compared withthose obtained in the presence of auxins (indole-3-acetic acidand 2:4-dichlorophenoxyacetic acid) in the external medium.The courses of positive curvature resulting from short exposures(40 minutes) and also subsequent recovery phenomena on a horizontalklinostat have been followed. A photographic recording techniqueallowed the determination of absolute growth-rates of both upperand lower sides of the root during the course of each experiment. Positive curvature started at its maximum rate (0.30–0.32deg./min.) after a reaction time of 11.5 minutes and continuedconstant at that rate for about 60 minutes after stimulationceased. Recovery took place at a similar rate of curvature andwas complete after a further 150–200 minutes. During thephase of positive curvature overall root growth-rates were considerablyreduced and were slowly restored to normal during recovery. Low concentrations (1 part in 10¹¹) of both auxins increasedthe rate of positive curvature by 30–40 per cent. andshortened the reaction time roughly in proportion. The growth-ratesof both sides of the root were increased to the same extentduring both curvature and recovery. High concentrations (10^–8IAA and 3.10^–8 2: 4-D)reduced the rates of curvature by 50 per cent., lengthened thereaction time, and inhibited the growth of both sides of theroot during both curvature and recovery. Neither concentration of either auxin otherwise affected thetime course of response and recovery. It is suggested that geotropic response is due to the de novoproduction of an endogenous inhibitor in the extending cellsof the lower side of the root whence it may later spread tothe upper side. The complete independence of the growth actionsof this inhibitor and of the applied auxins suggests that itis not indole-3-acetic acid or any similar compound. Recoverymay be very largely independent of both inhibitor and auxinsand due to the action of another growth factor limiting celllength. The implications of these findings and of the attendant theoriesare fully discussed.     

Effect of {alpha}-Tomatine on the Response of Wheat Coleoptile Segments to Exogenous Indole-3-acetic Acid

A concentration of 10^–5 M tomatine had no effect on leakagefrom, or elongation of, wheat coleoptile segments, but consistentlyreduced IAA-enhanced extension growth by c. 50 per cent. Therewas no evidence of chemical interaction between the alkaloidand the auxin in solution, and IAA action was not affected bypre-treatment for up to 3 h with 10^–5 M tomatine. Studieswith [2-¹⁴C]IAA revealed that 10^–5 M tomatine did notinhibit uptake of auxin into segments. The effect of pre-treatingsegments for up to 3 h with IAA could be virtually nullifiedby 10^–5 M tomatine, as could also IAA-induced changesin properties of coleoptile cell walls. Results are discussedin relation to the ability of tomatine to disrupt membrane functionand to current hypotheses implicating membranes in the primaryaction of auxin.     

Possible Roles of Methyl Glucoside andMyo-inositol in the Opening of Cut Rose Flowers

Methyl glucoside andmyo-inositol are present in all organs ofrose (Rosa hybridaL.). To investigate the possible role of thesecarbohydrates in the opening of cut roses, flowers with a 10,20 or 40-cm-long stem and a single flower bud (about 1.5 cmin diameter) were placed in water and flower opening and changesin sugar content in flowers and stems examined for 7 d. Thelonger the stem of the cut flower, the larger was the flowerdiameter. In stems, the concentration of carbohydrates, includingmethyl glucoside andmyo-inositol markedly decreased before floweropening. In petals, contents of glucose, methyl glucoside andmyo-inositolalso decreased before flower opening, but those of fructose,sucrose and xylose did not. When glucose and methyl glucosidewere added to the vase water (4%) flower opening was clearlypromoted; this was accompanied by an increase in methyl glucosideand fructose concentrations in petals. On the contrary,myo-inositolinhibited flower opening, and this was accompanied by an increaseinmyo-inositol and xylose concentrations in petals. These resultssuggest that methyl glucoside and/or its metabolites are transportedinto the petal cells, thereby lowering the osmotic water potentialand promoting flower opening.Myo-inositol is not readily metabolized,and exogenousmyo-inositol given at a high concentration mayact as an extracellular osmolyte, which inhibits water uptakeand flower opening.Copyright 1999 Annals of Botany Company Cut flowers, methyl glucoside,myo-inositol,Rosa hybrida,soluble carbohydrate.     

Two-Dimensional Protein Patterns of Arabidopsis Wild-Type and Auxin Insensitive Mutants, axr1, axr2, Reveal Interactions between Drought and Hormonal Responses

In order to detect gene products involved in Arabidopsis droughtadaptive strategy, 2D-PAGE protein patterns of two auxin-insensitivemutants, axr1, axr2, differentially affected in specific droughtresponses, were compared to the wild-type Columbia ecotype,in well-watered and drought-stressed conditions. Coupled tocomputer analysis of polypeptide amounts, 2D-electrophoresisrevealed subtle changes in protein expression induced by progressivedrought stress and/or mutations affecting the auxin responsepathway. The differential protein patterns of axr1 and axr2 were consistentwith their contrasting drought responses. The specific leafand root protein patterns of axr1 showed that this mutationdisrupts drought responses related to auxin regulation. In particular,the near absence of drought rhizogenesis in axr1 was associatedwith a root protein pattern closer to the well-watered thanto the water-stressed axr2 and Columbia wild-type root proteinpatterns. Also, the largely different effects of axr1 and axr2mutations suggest that they affect different pathways in auxinresponse. Several sets of polypeptides, whose regulation wasaffected by drought and/or mutation, were thus detected. Thesepolypeptides could play a role both in the auxin and the droughtresponse pathways. Their identification, through microsequencing,should be most informative. ⁴Current address: Laboratoire de BioénergétiqueCellulaire, Département d'Ecophysiologie Végétaleet de Microbiologie, Centre d'Etudes de Cadarache, 13108 SaintPaul lez Durance, France     

The Effects of Auxin on the Mechanical Properties in Vivo of Cell Wall in Hypocotyl Segments from Gibberellin-Deficient Cowpea Seedlings

Auxin-induced changes in the mechanical properties of cell wallwere examined by both positive and negative pressure jump methodsusing hypocotyl segments excised from the 3-day-old seedlingsof cowpea that has been treated with uniconazole, a potent inhibitorof the biosynthesis of gibberellins. In such segments (U-segments)that were deficient in endogenous gibberellin, auxin increasedonly the effective turgor (Pⁱ–Y) and did not change theextensibility () of cell wall. As a result, the extent of theauxin-induced promotion of growth was halved. However, auxinwas able to increase of U-segments that has been pretreatedfor two hours with GA₃ prior to the application of IAA. Measurementof intracellular pressure (P_i) with a pressure probe revealedthat auxin did not change Pⁱ in either U-segments or GA₃-pretreatedsegments. The results suggest that auxin can decrease the yieldthreshold of the cell wall (Y) independently of gibberellinbut can increase only in the presence of gibberellin. The differencebetween and Y in terms of their requirement for gibberellinto respond to auxin suggests that they are mutually separablemechanical properties that originate from different molecularprocesses that occur in the architecture of yielding cell walls. ³Present address: Ohishi, Enden, Mori-machi, Shuchi-gun, Shizuoka,437-02 Japan     

Transport and Accumulation of IAA-14C in Tumour-forming Nicotiana Hybrids

The polar transport of indol-3yl-acetic acid (IAA-2-¹⁴C) instem explants and decapitated shoots of tumour-prone Nicotianahybrids (2n, 3n, and 4n) was compared with that in the normal,non-tumorous parent species N. glauca and N. langsdorffii. Thetotal uptake of the auxin from donor blocks was greatest inthe hybrids and N. glauca. The velocity of the basipetal movementof IAA-¹⁴C was the same in all species tested, i.e. 8 mm/h.The transport capacity for the hormone, however, was decreasedin the three tumour-prone hybrids. Gas chromatography showedthat between 70 and 90 per cent of the transported auxin waspresent in the form of IAA, between 10 and 30 per cent in theform of indol-3yl-aldehyde (IAld). The basipetal transport exceeded the acropetal transport inyoung (third) intemodes of all plants studied, whereas in olderstem segments (tenth intenodes) the reverse was found. The polarity of auxin transport was less well expressed in thetumorous hybrids. Blocking the active transport by pre-treatment of stem cuttingswith 2,4-dinitrophenol (2,4-DNP) caused a drastic reductionin the polar IAA-¹⁴C movement; in all plants tested the auxintransport was reduced to the same low level. The accumulation of auxin at the base of cuttings was higherin N. glauca and the 2n hybrid than in N. langsdorffii, i.e.about seven times higher after 1-h and three times higher after12-h transport experiments. The release of ¹⁴C from the cuttinginto an agar receiver block, however, was markedly reduced inthe 2n hybrid, whereas in N. glauca the labelled substancesmoved more freely into the receiver blocks. Differences in the capacity for the accumulation and the releaseof IAA-¹⁴C in hybrid and N. glauca stem tissues were studiedusing decapitated greenhouse plants wounded by incision abovethe fourth internode. Accumulation of the auxin occurred onlyabove the wound-cut in hybrid plants. This observation is consistentwith the view that tumour formation on hybrid stems occurs atsites of wounding. Our data suggest an elevated auxin levelto be present during tumour initiation at these sites. These results on polar transport and accumulation of IAA-¹⁴Cin tumorous Nicotiana plants together with our previous dataon various endogenous auxins suggest that the induction of neoplasticgrowth in tobacco plants is correlated with increased auxinlevels and an accumulation of the hormone at sites of wounding.     

Distribution of Calcium, Potassium and Phosphorus in Helianthus annuus Hypocotyls and Zea mays Coleoptiles in Relation to Tropic Stimuli and Curvatures

Studies have been made of the distribution of ⁴⁵Ca, ⁴²K, totalK⁺ and ³²P between the concave and convex sides of segmentsof hypocotyl of Helianthus annuus and coleoptiles of Zea maysduring curvatures induced by gravity, unilateral illuminationor unilateral applications of indol-3yl acetic acid (IAA). Theelements were fed to the roots of seedlings for a 3–4h pretreatment period. Distributions in segments in intact seedlingswere compared with those in explanted segments deprived of acontinuing supply of the element concerned in order to separatepossible differential transport of the element from the rootsfrom any real movement across the organ from side to side. Withall three treatments, and in both explants and intact plants,⁴⁵Ca concentrations (on both fwt and dwt bases) were higheron the convex side. There was evidence of differential transportto the two sides and also of a direct movement across the parenchymafrom one side to the other. In organs where curvature was inhibitedby low temperatures (4 °C in geotropic experiments) or bythe antitropistic agent, N-1-naphthylphthalamic acid, no concentrationdifferences arose between the two sides. After the tropic stimulithe onset of the concentration differences preceded the onsetof curvature significantly, indicating that those differenceswere not caused by differential growth of the organ. The diuretic,mersalyl, applied unilaterally produced differences in elementconcentration of the same order and kind as similar treatmentwith IAA, but caused no growth curvatures. It is concluded that the movement of elements in tropicallycurving tissues, although apparently obligately-linked withcurvature, is not the result of that curvature or its cause,but is in some as yet undefined way an outcome of auxin gradientsin the tissue.     

Effect of kinetin on auxin uptake and distribution in normal and tumor-prone Nicotiana shoots

Stem segments of non-tumorous Nicotiana glauca and N. langsdorffiiplants and of their tumor-producing amphidiploid F₁ hybrid weretreated with 6-furfurylaminopurine (kinetin) prior to transporttests with applied labeled indoleacetic acid (IAA-2-¹⁴C). Kinetin-treatmentsincreased the uptake of IAA in non-tumorous shoots; the IAAuptake by N. langsdorffii segments was increased up to 3-fold.The auxin uptake in stem-segments of the tumor-forming hybrid,however, could not be increased significantly by kinetin. Theeven distribution of IAA-¹⁴C in segments of normal and tumorproneNicotiana shoots is stimulated by kinetin. Data are discussedin conjunction with previous results on auxin transport andtumorformation in Nicotiana. (Received August 8, 1972; )     

The Effects of Externally Applied 3-indolylacetic Acid on Phototropic Induction and Response in the Coleoptile of Avena

The effects of intermittent immersion of Avena seedlings insolutions of IAA on the response of the coleoptiles to unilateralillumination in the region of that producing the second positivecurvature were studied by means of automatic time-lapse photographywhich enabled the growth-rate and curvature to be recorded simultaneously. Phototropic induction occurred even after the coleoptiles hadabsorbed sufficient IAA from a 10^-4 M. solution to raise theirrate of elongation to about twice the normal value. Phototropiccurvature, which had been temporarily inhibited by a curvaturein the opposite direction induced by the IAA, became evidentas soon as this curvature had ceased to operate. In coleoptiles, supplied with IAA after the commencement ofa phototropic curvature, the response was temporarily suppressed.It was resumed as soon as the effects of the exogenous IAA haddisappeared. The ability of the coleoptiles to produce a slight phototropicresponse persisted even when their growth-rate had been greatlyreduced by previous removal of the endosperm. Increasing thegrowth-rate by supplying the starved seedlings with IAA or sucrose,separately or together, failed to increase the response. Decapitation did not prevent phototropic induction, but delayedthe onset of the response. Application of IAA by intermittentimmersion in a 0.1 mg./l. solution, after the decapitated coleoptileshad been exposed to unilateral illumination, increased the rateof growth but reduced the response. The results suggest that in these experiments phototropic inductionwas not mediated by any direct action of light on the displacement,inactivation, or rate of synthesis of an endogenous auxin. Theyare in agreement with the hypothesis that the stimulus causedan asymmetrical distribution of a co-factor of auxin.     

Effects of Morphactin on Indol-3yl-acetic Acid Transport, Growth, and Geotropic Response in Cereal Coleoptiles

The effects of the morphactin 2-ehloro-9-hydroxyfluorene-9-carboxylicacid methyl ester [CFM] on growth, geotropic curvature and transportand metabolism of indol-3yl-acetic acid [IAA-5-³H] in the coleoptilesof Zea mays and A vena saliva have been investigated. A strongcorrelation has been found to exist between the inhibition ofthe geotropic response and the inhibition of auxin transport.CFM supplied at concentrations sufficient to abolish auxin transporthas been shown to promote the elongation of Zea, but not ofAvena, coleoptile segments. CFM does not change the patternof metabolism of IAA in Zea coleoptile segments. In these segmentsIAA is metabolized when its concentration is high, but the radioactivitytransported basipetally, or laterally in geotropically stimulatedcoleoptiles, is virtually confined to the IAA molecule. Radioactivityexported into the basal receiver blocks is wholly confined toIAA. It is concluded that CFM inhibits the geotropic responsein coleoptiles by suppression of the longitudinal and lateralauxin transport mechanisms. The growth-promoting propertiesof this substance cannot be linked with its effects on eitherauxin metabolism or transport.     

The Role of Basipetal Auxin Transport in the Positional Control of Abscission Sites Induced in Impatiens sultani Stem Explants

If segments of Impatiens sultani stem are explanted and incubated,separation layers often form across them and lead to abscission.To test the suggested role of auxin concentration in controllingthe position of abscission sites, explants were labelled byapplying [¹⁴C]IAA to the shoot tip 4 h prior to explanting;transport of auxin applied in this way seems to resemble thatof endogenous auxin. During subsequent incubation of explantsfor 20 h, basipetal transport resulted in ¹⁴C accumulating justabove the base of the explants (nearly 80 % in the bottom 4mm of 24 mm explants). In internodal explants that had beenwounded at explanting by incising one side so as to sever avascular bundle, and in nodal explants with the leaf removed,the ¹⁴C also accumulated just above the wound or node to abouttwice the concentration otherwise expected; this accumulationwas probably due to basipetal transport being impeded by vasculardiscontinuity at the wound or node. Accumulation just abovethe base, or above a wound or node, resulted in gradients of¹⁴C concentration (presumably reflecting endogenous auxin concentration)decreasing in the morphologically upward direction at each ofthese three positions where abscission sites tend to occur. Impatiens sultani, abscission, auxin, IAA, node, polarized transport, positional control, separation layer, wounding     

The Effects of Cytokinins and ABA on Stomatal Behaviour of Maize and Commelina

Epidermal strips and leaf fragments of Commelina and leaf fragmentsof maize were incubated on solutions containing naturally-occurringor synthetic cytokinins and/or ABA. The effects of these treatmentson stomatal behaviour were assessed. Cytokinins alone did notpromote stomatal opening in either species but concentrationsof both zeatin and kinetin from 10^–3 to 10^–1 molm^–3 caused some reversal of ABA-stimulated closure ofmaize stomata. The reversal of the ABA effect increased withincreasing cytokinin concentration. Cytokinins had no effecton ABA-stimulated closure of Commelina stomata. When appliedalone, at high concentration (10^–1 mol m^–3), toCommelina epidermis or leaf pieces both zeatin and kinetin restrictedstomatal opening. Key words: ABA, Cytokinins, Stomata, Maize, Commelina     

Auxin Stimulates Cl-Uptake by Oat Coleoptiles

The effects of auxin on net ion fluxes near parenchyma of oatcoleoptiles were studied using the non-invasive MIFE systemto measure specific ion fluxes using ion selective microelectrodes.Application of 10 µM1-naphthaleneacetic acid (NAA) for3 h caused doubling of coleoptile segment growth, without changingthe pH of the unbuffered bathing solution from pH 5.4 duringthat time. Short term experiments revealed that auxin led toan immediate three-fold increase of chloride influx to 1200nmol m^-2s^-1, maintained for at least 1 h. In the first minutesafter auxin application, proton fluxes were small (-25 nmolm^-2s^-1, an efflux) and tended to decrease, whereas potassiumand calcium fluxes changed little, fluctuating from -100 to0 nmol m^-2s^-1and from -15 to 0 nmol m^-2s^-1, respectively. Itis suggested that one target of auxin action in plant cellsis the plasma membrane chloride transport system mediating increasedchloride uptake.Copyright 1998 Annals of Botany Company Auxin, chloride transport, ion flux,Avena sativaL., oat.     

Effect of cycloheximide and cordycepin on auxin-induced elongation and {beta}-glucan degradation of noncellulosic polysaccharides of Avena coleoptile cell wall

The effect of cycloheximide (10^–5 M) and cordycepin (10^–4M) used as protein and RNA synthesis inhibitors, respectively,on auxin action in noncellulosic ß-glucan degradationof Avena coleoptile cell wall was investigated. Both depressedauxin-induced ßglucan degradation of the cell wallas well as auxin-induced elongation and cell wall loosening,suggesting that the process of ß-glucan degradationof the cell wall is closely associated with cell wall looseningand that auxin enhances the activity of an enzyme for ß-glucandegradation through de novo synthesis of RNA and protein butnot through activation of the enzyme in situ. Kinetic studywith the inhibitors showed that RNA metabolism involved in ß-glucandegradation was stimulated by auxin treatment of only 15 minwhile a longer lag phase (about 1 hr) existed for the synthesisof the enzyme. (Received December 16, 1978; )     

Auxin and Ethylene-stimulated Adventitious Rooting in Relation to Tissue 9

We have previously shown that both endogenous auxin and ethylenepromote adventitious root formation in the hypocotyls of derootedsunflower (Helianthus annuus) seedlings. Experiments here showedthat promotive effects on rooting of the ethylene precursor,1-aminocyclopropane-l-carboxylic acid (ACC) and the ethylene-releasingcompound, ethephon (2-chloro-ethylphosphonic acid), dependedon the existence of cotyledons and apical bud (major sourcesof auxin) or the presence of exogenously applied indole-3-aceticacid (IAA). Ethephon, ACC, aminoethoxyvinylglycine (an inhibitorof ethylene biosynthesis), and silver thiosulphate (STS, aninhibitor of ethylene action), applied for a length of timethat significantly influenced adventitious rooting, showed noinhibitory effect on the basipetal transport of [³H]IAA. Theseregulators also had no effect on the metabolism of [³H]IAA andendogenous IAA levels measured by gas chromatography-mass spectrometry.ACC enhanced the rooting response of hypocotyls to exogenousIAA and decreased the inhibition of rooting by IAA transportinhibitor, N-1-naphthylphthalamic acid (NPA). STS reduced therooting response of hypocotyls to exogenous IAA and increasedthe inhibition of rooting by NPA. Exogenous auxins promotedethylene production in the rooting zone of the hypocotyls. Decapitationof the cuttings or application of NPA to the hypocotyl belowthe cotyledons did not alter ethylene production in the rootingzone, but greatly reduced the number of root primordia. We concludethat auxin is a primary controller of adventitious root formationin sunflower hypocotyls, while the effect of ethylene is mediatedby auxin. Key words: Auxin, ethylene, adventitious rooting, sunflower