The Relationship between Levels of Endogenous Gibberellins and the Response of Vigna Hypocotyls to Exogenous Indole-3-Acetic Acid

Segments excised from the upper and the lower parts of cowpea(Vigna unguiculata L.) hypocotyls were compared in terms oftheir responses to exogenous indole-3-acetic acid (IAA) in relationto their endogenous levels of gibberellin. Growth of the segmentswas measured continuously during xylem perfusion with a lineardifferential transformer. IAA induced a burst of elongationin the upper segments but only slight promotion of growth inthe lower segments. Treatment with uniconazole, a potent inhibitorof the biosynthesis of gibberellins, reduced the responsivenessof the upper segments to exogenous IAA to about one half ofthe control value. Pre-perfusion with GA₃ of such segments fortwo hours prior to application of IAA, partially restored theresponsiveness to IAA. Analysis by GC/MS identified GA₁, GA₄,GA₉ GA₂₀ and GA₅₁ as native gibberellins in the hypocotyls ofcowpea seedlings. Analysis by GC/SIM also showed that the physiologicallyactive gibberellins (GA₁ and GA₄) were located mainly in theupper part of the hypocotyl and the treatment with uniconazolemarketly reduced the endogenous level of gibberellins thereto less than 11% of the control level. These results suggestthat levels of endogenous gibberellins possibly control theresponse to IAA in these segments. (Received May 12, 1994; Accepted November 15, 1994)     

Gibberellin A3 Causes a Decrease in the Accumulation of mRNA for ACC Oxidase and in the Activity of the Enzyme in Azuki Bean (Vigna angularis) Epicotyls

Differential screening, aimed at the isolation of cDNA clonesof mRNAs whose accumulation is influenced by GA₃, resulted inthe isolation of a cDNA clone of an mRNA whose level was decreasedby GA₃ in segments of epicotyls of Vigna angularis. The putativeprotein encoded by this cDNA resembled the 1-aminocyclopropane-l-carbox-ylateoxidases (ACC oxidases) identified in other plant species (about80% homology at the amino acid level). Thus, the correspondinggene was designated AB-ACO1 (azuki bean ACC oxidase). GA₃ alsodecreased the activity of ACC oxidase in azuki bean epicotyls,but it did not decrease the rate of ethylene evolution. In fact,GA₃ increased the rate of ethylene evolution and the level ofACC. Thus, GA₃ seemed to increase the production of ethyleneby promoting the synthesis of ACC. (Received January 10, 1997; Accepted July 31, 1997)     

cDNA Cloning and Characterization of a Gibberellin-Responsive Gene in Hypocotyls of Cucumis sativus L.

A cDNA clone corresponding to a gibberellin-responsive gene(CRG16) was isolated from cucumber hypocotyls. CRG16 was deducedto encode an extremely hydrophobic protein of 65 amino acids.The deduced sequence exhibited no significant homology to otherproteins. Levels of CRG16 mRNA reflected the gibberellin-inducedelongation of cucumber hypocotyls. (Received December 16, 1995; Accepted April 22, 1996)     

Interaction of a Brassinosteroid with IAA and GA3 in the Elongation of Cucumber Hypocotyl Sections

A synthetic brassinosteroid, 22,23(S,S)-homobrassinolide (hBR),was examined for its interaction with IAA and GA₃ in the elongationof hypocotyl sections of light-grown cucumber (Cucumis salivusL. cv. Aonagajibai) seedlings. hBR alone was less active thanIAA. Its optimal concentration was around 10 µM and thelowest effective concentration between 10 and 100 µM,which is more than 100 times higher than that of brassinolide.hBR was more active in sections from younger seedlings. Itsgrowth-promoting effect was negated or greatly reduced by inhibitorsof auxin-induced elongation such as p-chlorophenoxyisobutyricacid and kinetin. hBR acted synergistically with IAA and 2,4-Dbut not with GA₃ showing only an additive effect. Sequentialtreatment of sections with hBR and then with IAA also resultedin synergistic enhancement of auxininduced elongation, but whenthe order of treatment was reversed, hBR was inactive. The synergisticeffect was obtained with 1 h pretreatment with hBR and couldbe reduced by subsequent washing with water. There was no sequentialinteraction between hBR and GA₃. The synergistic pretreatmenteffects of hBR and GA₃ were simply additive to each other. Amembrane-bound ATPase inhibitor, dicyclohexylcarbodiimide, inhibitedthe hBR-induced elongation, but did not affect GA₃-induced elongation.The findings led to the conclusion that brassinosteroids enhanceauxin action and possess growth-promoting activity which isindependent of that of gibberellin. (Received November 9, 1984; Accepted February 18, 1985)     

Gibberellin-Induced Changes in Starch Content in Isolated Chloroplasts of Light-Grown Cucumber Hypocotyls

Gibberellin A₃ (GA₃) was found to reduce the starch contentin chloroplasts isolated from light-grown cucumber (cv. Aonagajibai)hypocotyls. Chloroplasts incubated with 50 mM sucrose showedan increase in starch content. The GA₃-induced reduction occurredboth in the presence and absence of exogenous sucrose. GA₃ hadno effect on the level of starch already formed from exogenoussucrose. (Received April 4, 1984; Accepted June 7, 1984)     

Control by Light of Hypocotyl Elongation and Levels of Endogenous Gibberellins in Seedlings of Lactuca sativa L.

Four 13-hydroxygibberellins, gibberellin A₁ (GA₁), 3-epi-GA₁,GA₁₉ and GA₂₀ were identified by full-scan GC/MS in extractsof lettuce seedlings (Lactuca sativa L. cv. Grand Rapids). Theresults suggest that the early-13-hydroxylation biosyntheticpathway to GA₁ functions in the lettuce seedlings. It was alsofound that GA₁ is active per se in the control of hypocotylelongation in lettuce seedlings. To investigate the relationshipbetween control by light of hypocotyl elongation and levelsof endogenous GAs in lettuce, endogenous levels of GAs werequantified by radioimmunoassay in seedlings that had been grownfor 5 days in the dark (5D) and in those that had been grownfor 4 days in the dark and then under white light for 1 day(4D1L). The endogenous level of GA₁ in the upper and lower partsof hypocotyls in 5D seedlings was about four times higher thanthat in 4D1L seedlings. The response of explants (hypocotylsegments with cotyledons) from dark-grown seedlings to GA₁ isknown to be similar in the dark and under white light when theexplants are treated with inhibitors of the biosynthesis ofGA. Therefore, the above information suggests that the highlevel of GA₁ in hypocotyls of dark-grown seedlings is responsiblefor the rapid elongation of hypocotyl, while irradiation bywhite light decreases the endogenous level of GA₁ in the hypocotylswith a resultant decrease in the rate of hypocotyl elongation. (Received March 13, 1992; Accepted May 21, 1992)     

Auxin-gibberellin relationships in their effects on hypocotyl elongation of light-grown cucumber seedlings II. Effect of GA3-pretreatment on IAA-induced elongation

IAA-induced growth of light-grown cucumber hypocotyl sectionsis markedly enhanced by GA₃-pretreatment of the sections; thereis a distinct synergism between IAA and GA₃. Water pretreatmentalso enhances IAA-induced growth. On the other hand, IAA-pretreatedsections showed practically no further growth in response topost treatment with GA₃. The enhancing effect of GA₃ is obtainedwith only 30 min pretreatment, the maximum effect occuring with2 hr pretreatment. Pretreatment longer than 8 hr is less effective.This enhancing effect of GA₃ can be observed soon after posttreatment with IAA. The response of GA₃-pretreated sectionsto IAA is greater in pretreatment with higher concentrationsof GA₃, and higher degrees of synergism between IAA and GA₃are obtained at IAA concentrations less than 10^-4 M. This synergisticinteraction between GA₃ and IAA is more marked in aged hypocotylsections than in young sections. From these results we concludedthat gibberellin sensitizes hypocotyl cells to the subsequenteffect of auxin on cell elongation. (Received October 6, 1973; )     

The Interaction of Genetic, Environmental, and Hormonal Factors in Stem Elongation and Floral Development of Cucumber Plants

Hypocotyl length was found to vary between cucumber plants carryingdifferent genes controlling sex expression. Among lines havingonly unisexual flowers (genotype M/M), the homozygous monoeciousplants (st⁺/st⁺) had significantly longer hypocotyls than theirgynoecious counterparts (st/st), heterozygous gynoecious plants(st+/st) being intermediate. Similarly, hypocotyls of plantsof an andromonoecious line (st⁺/st⁺ m/m) were significantlylonger than in their hermaphrodite counterparts (st/st m/m).Differences in intemode length were also significant and inthe same direction. Since stem and particularly hypocotyl elongationin cucumber is known to be very sensitive to applied gibberellin,these findings suggest the existence of differences in the effectivelevels of endogenous gibberellins in the different sex types,higher levels being correlated with stronger male tendency.This conclusion is in good agreement with the known effect ofapplied gibberellin on sex expression (enhancement of the maletendency) in cucumber. Application of gibberellin (GA₄+GA₇) and exposure to ‘summer’conditions (long days and relatively high temperature) inhibitedthe development of pistillate flowers while ‘winter’conditions (short days, lower temperature) had a similar effecton staminate flowers. The effect was in either case specific,that is, limited to flower development. It is concluded thatexogenous and endogenous gibberellins affect not only the initiation,but also the further development, of flowers in the cucumber.     

The influence of various plant hormones on the stimulatory action of red light on greening in excised etiolated cotyledons of cucumber

In etiolated cotyledons of cucumber (Cucumis sativus L. cv.Aonagajibai), preillumination with a short pulse of red lighteliminated the lag phase and stimulated Chl formation in thelinear phase during subsequent continuous illumination. Thistwofold effect was clearly distinguishable by varying the lengthsof the dark periods after preillumination. Pretreatment of excisedcotyledons with BA, GA₃ ethylene, or IAA stimulated Chl formationduring subsequent illumination. The effects of BA and GA₃ seemedindependent of both kinds of red light effects. However, ethyleneand IAA interacted with red light in increasing the rate ofChl formation during the linear phase. This may provide someclue to the red light action on Chl formation through its probablestimulation of ethylene production. (Received June 7, 1978; )     

Gibberellin-Induced Suppression of Chloroplast Starch Formation from Exogenous Sucrose in Isolated Epidermis of Light-Grown Cucumber Hypocotyls

The effects of gibberellin A₃(GA₃) on chloroplast starch formationfrom exogenous sucrose in epidermal strips of light-grown cucumber(Cucumis sativus L. cv. Aonagajibai) hypocotyls were studied.Chloroplast starch formation was measured by counting microscopicallythe number of I₂KI stained chloroplasts. In the presence ofsucrose (1–50 mM) and in light, chloroplast starch formationoccurred rapidly for 5 hr and then the rate declined. GA₃ (100µM) simultaneously supplied with sucrose clearly suppressedboth the rate and the degree of starch formation. When the epidermiswas preincubated in the dark with sucrose in the presence orabsence of GA₃ and then post-incubated in light with bufferonly in the presence or absence of GA₃, starch formation wassuppressed to the same degree by GA₃ given either in the pre-or post-incubation period. When the epidermis was preincubatedin the dark with GA₃ alone and then transferred to light forpost-incubation with sucrose alone, GA₃ suppressed the initialrate of starch formation during the post-incubation period.The degradation of chloroplast starch formed in advance fromexogenous sucrose in light was not significantly affected byGA₃ These results are discussed in relation to the mechanismof the GA₃ action and also to the GA₃-induced decrease in theosmotic potential of the cell. (Received February 2, 1982; Accepted May 31, 1982)     

Comparative Effects of lndole-3-acetic acid, Abscisic acid, Gibberellic acid and 6-Benzylaminopurine on the Dark- and Light-induced Pulvinar Movements in Cassia fasciculata Michx

Effects of plant hormones were examined on the dark- and light-inducedmovements of Cassia fasciculata. Indole-3-acetic acid (IAA),gibberellic acid (GA₃) and 6-benzylaminopurine (6-BAP) inhibitedthe scotonastic movement whereas abscisic acid (ABA) enhancedit. After brief treatments (5 to 30 min), the ABA effect wasinhibitory rather than promotional. Hormonal treatment in theacidic range gave the best physiological response for ABA, butthe greatest efficiency of IAA, GA₃ and 6-BAP was obtained withpH values close to neutrality. Three to 5 h were needed beforeexpression of the physiological effect triggered by GA₃ and6-BAP, while 5 min treatments were sufficient for IAA and ABA.Light-induced movements were largely enhanced by IAA and slightlyby GA₃ but inhibited by 6-BAP and ABA. The results are discussedin relation to the ionic changes in the pulvinar motor cells,regulating leaflet movements. Key words: Abscisic acid, auxins, cytokinins, gibberellic acid, pulvinar movements     

Actinomycin D Inhibits the GA3-Induced Elongation of Azuki Bean Epicotyls and the Reorientation of Cortical Microtubules

Actinomycin D inhibited the elongation of epicotyl segmentsfrom azuki bean seedlings that was induced by simultaneous treatmentwith IAA and GA₃. The drug also inhibited the elongation ofthe segments that was caused by IAA alone when it was appliedtogether with IAA. When the segments were pretreated with GA₃and then incubated with IAA, GA₃ promoted the elongation causedby IAA and brought about a predominance of transverse corticalmicrotubules (MTs) in the epidermal cells of the segments. Thechange in the arrangement of MTs caused by pretreatment withGA₃ was evident 1 h after the start of subsequent incubationwith IAA when the effect of pretreatment with GA₃ on the elongationhad not yet become apparent. Pretreatment with GA₃ did not causeany change in the arrangement of MTs when GA₃-pretreated segmentswere not incubated subsequently with IAA. Although actinomycinD applied before treatment with IAA did not inhibit the IAA-inducedelongation, the drug diminished the promotion of the elongationcaused by pretreatment with GA₃ and prevented GA₃ from bringingabout a predominance of transverse MTs when the drug was appliedduring the pretreatment with GA₃. GA₃-induced synthesis of mRNA seems to be involved in the promotionby GA₃ of IAA-induced elongation and in the GA₃-induced rearrangementof cortical MTs. (Received June 15, 1993; Accepted August 16, 1993)     

Zinc Deficiency Affects the Levels of Endogenous Gibberellins in Zea mays L.

Zinc deficiency in Zea mays L. markedly reduced the level ofGA₁, but not GA₂₀, suggesting blockage of 3rß-hy-droxylation.The level of IAA was also decreased although not as markedly.Castasterone was affected less than IAA by zinc deficiency. (Received February 24, 1997; Accepted June 24, 1997)     

Hormonal Regulation of Gametangial Formation in the Moss Bryum argenteum Hedw

Phytohormones such as auxins, cytokinins, gibberellins, andabscisic acid differentially affect gametangial induction inmale and female clones of Bryum argenteum. Both IAA and GA³increased the percentage of fertile gametophores in the maleclone, and inhibited the response in the female clone. GA₃ wasmore effective than IAA in eliciting the response in the maleclone. Cytokinins, on the other hand, increased the productionof fertile gametophores in the female clone, and inhibited itslightly in the male clone. The two cytokinins tested (kinetinand DMAAP) were almost equally effective for the female clone. An Interaction of IAA and kinetin nullified their individualinhibitory effects on the female and male clones, respectively.Cyclic AMP prevented the inhibitory effect of kinetin in themale clone; whereas, in the female clone, it stimulated theresponse elicited by kinetin. Abscisic acid (ABA) acted as ageneral inhibitor of vegetative growth and gametangial inductionin this moss. However, the inhibition of gametangial inductionwas greater in the female clone which is also more sensitiveto ABA than the male clone.     

Mode of Action of IAA and GA3 on Root and Shoot Growth of Epiphyllous Buds of Bryophyllum tubiflorum

Darkness and GA₃ stimulate the elongation of the first internodebut inhibit the production of roots while IAA inhibits internodalelongation but promotes the production of roots on epiphyllousbuds of Bryophylhum tubiflorum. Cycloheximide inhibits both,implicating the synthesis of proteins in the growth of bothroot and shoot. Even pre-treatment of buds with cycloheximidefor 4 h inhibits rooting as well as internodal elongation whenthese are subsequently transferred to IAA or GA₃. On the otherhand, pre-treatment with IAA or GA₃ even for 8 h does not alleviatethe inhibitory effect of cycloheximide suggesting that thereis a lag period between the application of these regulatorsand the synthesis of proteins caused by them.     

Gibberellin-colchicine interaction in elongation of azuki bean epicotyl sections

In azuki bean (Azukia angularis = Vigna angularis) epicotylsections, gibberellin A₃ (GA₃) enhanced the growth promotingeffect of indoleacetic acid (IAA), but showed no growth effectwhen applied alone. Sections showed practically no cell division.The promoting effect of GA₃ on section growth seems to be dueto its promoting effect on cell elongation. The diameters of sections treated with IAA increased, but thediameters of sections treated with GA₃ together with IAA remainedconstant. GA₃ seems to suppress cell expansion in a directiontransverse to the cell axis. Colchicine at a concentration with no inhibiting effect on IAA-inducedelongation almost completely reversed the effect of GA₃ On the basis of these results, the participation of wall microtubulesin GA₃-induced elongation is discussed. (Received October 22, 1971; )     

Inoculation with Azospirillum lipoferum Affects Growth and Gibberellin Status of Corn Seedling Roots

Maize (Zea mays L., hybrid Cargill 147) seedlings, grown inaseptic conditions, were inoculated with three strains of Azospirillumlipoferum (Al op 33, Al iaa 320, and ATCC 29708) or culturedin different concentrations of indol-3-acetic acid (IAA) orgibberellin A₃ (GA₃). After 48 h, root length, root surfacearea, root dry weight, and shoot dry weight were measured inall treatments. Gibberellin content was evaluated in selectedroots of control and Azospirillum inoculated seedlings by gaschromatography-mass spectrometry-selected ion monitoring withthe use of deuterated gibberellins as internal standards. Thethree strains of A. lipoferum, IAA (2 ng ml^–1), and GA₃(40 to 400 pg ml^–1) significantly enhanced root growth.Improvement of root hair growth and density was obtained mainlywith A. lipoferum strain Al op 33 and GA₃ 40 pg ml^–1.GA₃ was identified by gas chromatography-mass spectrometry (byboth, full scan and selected ion monitoring) in a free acidfraction from roots of the seedlings inoculated with A. lipoferum.In the roots of the non inoculated seedlings GA₃ was found afterhydrolysis of a fraction expected to contain glucosyl conjugates. (Received April 26, 1993; Accepted September 27, 1993)     

Enhancement of Gibberellic Acid-stimulated Hypocotyl Elongation of Lettuce (Lactuca sativa L. cv. Grand Rapids) by Phlorizin and Light

The interaction of light, gibberellic acid (GA₃), and phlorizinin the growth of lettuce (Lactuca sativa L. cv. ‘GrandRapids’) hypocotyls was investigated. At all concentrationsof GA₃, phlorizin enhanced GA₃-induced growth at luminous intensitiesabove 50 ft-c (continuous light). Without GA₃, phlorizin hadno effect on hypocotyl growth in the light but it inhibitedgrowth in the dark. Both seedlings and hypocotyl sections respondedto phlorizin in the presence of GA₃. There was no iteractionbetween phlorizin and KCl. Water-growth was severly inhibitedby light. GA₃,-induced growth was slightly inhibited by light,and then only at luminous intensities above 50 ft-c. Thus, relativeto H₂O-growth, GA₃-induced growth increased with increasingluminous intensity up to 450 ft-c, where it reached saturation.It seems that a synergism may exist between light and GA₃ aswell as between phlorizin and GA₃. Lactuca sativa L, lettuce, hypocotyl elongation, gibberellic acid, phlorizin, light     

GA3和IAA对慈竹综纤维和叶绿素含量动态积累的调控效应

以慈竹为材料,研究不同浓度和配比的GA₃和IAA对综纤维和叶绿素含量动态积累的调控效应,为纸浆用竹的遗传改良研究提供理论依据。研究结果表明, GA₃和IAA处理对慈竹综纤维动态积累调控作用具有差异。处理前30 d内,GA₃50IAA200处理慈竹综纤维积累强度高于GA₃200IAA50处理,40~50 d时,则反之。GA₃和IAA处理的综纤维最终水平明显高于空白对照,差异达极显著水平。GA₃和IAA处理能提高慈竹叶绿素含量,GA₃200IAA50处理慈竹叶绿素含量高于GA₃50IAA200处理。相关分析结果表明,叶绿素含量与综纤维含量间呈不显著正相关关系。     

Effects of Fluorogibberellins on Plant Growth and Gibberellin 3r{beta}-Hydroxylases

3rß-Fluorogibberellin A₉ (3rß-fluoro-GA₉),3rßfluoro-GA₂₀, 3rß-fluorodeoxygibberellinC (3rß-fluoro-DGC) and 13-fluoro-GA₉ were prepared,and their effects on plant growth and gibberellin (GA) 3rß-hydroxyIaseswere examined. 3rß-Fluoro-GA₉ and 3rß-fluoro-GA₂₀promoted the growth of dwarf rice (Oryza sativa L. cv. Tan-ginbozu)seedlings to three times higher than the control seedlings ata dosage of 3 µ plant^–1, and 3rßfluoro-DGCto twice higher at the same dosage. 3rßg-Fluoro-GA₉was active in cucumber (Cucumis sativus L.) hypocotyl assay,its activity being about one-thirtieth as much as that of GA₄.3rß-Fluoro-GAs were active per se in promoting theshoot elongation of rice. 3rß-Fluoro-DGC inhibitedthe 3rß-hydroxylation of [³H₂]GA₉ to [³H]GA₄ by GArß-hydroxylase from bean (Phaseolus vulgaris L.),but 3rß-fluoro-GA₉ and 3rß-fluoro-GA₂₀ didnot show any effects on the enzyme activity. These 3rß-fluoro-GAsalso showed no or only a weak inhibitory effect on the rß-hydroxylasefrom pumpkin (Cucurbita maxima L.). 13-Fluoro-GA₉ promoted growthof rice and cucumber seedlings, and inhibited the 3rß-hydroxylasesfrom both bean and cucumber. 13-Fluoro-GA₉was converted into13-fluoro-GA₄ and 2,3-didehydro-13-fluoro-GA₉, in a cell-freesystem from bean, and conversion of 13-fluoro-GA₉ into 13-fluoro-GA₄was also observed in a cell-free system from pumpkin. Theseresults suggest that 13-fluoro-GA₉ is one of the substratesof GA 3rß-hydroxy-lases, and that 13-fluoro-GA₉ isactive as a result of the conversion to 13-fluoro-GA₄ in riceand cucumber seedlings. (Received October 27, 1997; Accepted March 13, 1998)