Antagonistic and Synergistic Interactions between Ancymidol and Gibberellins in Shoot Growth of Cucumber (Cucumis sativus L. )

Effects of the plant growth retardant, ancymidol, on the growthand morphology of the shoot system of cucumber (Cucumis sativusL. ) were investigated. Ancymidol inhibited stem elongation,reducing both number and length of internodes. Reduction inleaf area, attributable to a reduction in both cell size andnumber, was accompanied by an increase in chlorophyll per unitarea. The retardant decreased apical dominance and delayed anthesis.Gibberellic acid fully reversed ancymidol-induced inhibitionof stem elongation, internode length and production, and leafexpansion. GA_4/7 and ancymidol gave a synergistic promotionof stem elongation by increasing elongation of younger internodesand increasing internode production. Synergistic promotion ofpetiole elongation by this combination was also observed. Ancymidol,applied 7 d previously either to the shoot or root, severelyreduced the level of gibberellin-like activity in bleeding sapcollected from decapitated plants.     

Interactions of the Growth Retardants Daminozide and Piproctanyl Bromide, and Gibberellins A1, A3, A4+7, A5 and A13 in Stem Extension and Inflorescence Development in Chrysanthemum morifolium Ramat

Interactions between the growth retardants daminozide (a substitutedsuccinamic acid) or piproctanyl bromide (a quaternary ammonium,piperidinium compound), and a subsequent application of a singledose (40 µg) of either gibberellin A₁, A₃, A₄₊₇ or A₁₂,showed that, in Chrysanthemum morifolium Ramat. cv. Bright GoldenAnne, a strong interdependence exists between elongation ofthe lateral shoot and the rate of development of its terminalinflorescence. A₁, A₃, and A₄₊₇ were highly active in overcoming the restrictionson both internode extension and the rate of flower-bud developmentimposed by either retardant, suggesting that these two retardanteffects are caused by a deficiency of active gibberellins (GN).In the absence of retardant, A₁, A₃, and A₄₊₇ markedly increasedstem elongation, and flowering occurred earlier than in plantsreceiving neither retardant nor GN. A₁₃ the only 20-carbon GNtested, was much less active, while A₅ had a relatively greatereffect on the time of flowering than on shoot elongation. Thus,it is not necessarily the rate of stem extension which determinesthe rate of inflorescence development. The response to different amounts of A₁, A₃ or A₁₃ (1, 5, 10,20, or 50 µg per shoot) neither suggest that different‘threshold’ levels of a particular GN are requiredto induce increases in either stem elongation or in the rateat which inflorescences develop, nor did a change in the dosegiven lead to any consistent differential effect on these twoprocesses. Chrysanthemum morifolium Ramat., stem extension, inflorescence development, growth retardants, gibberellins     

Evidence that Daminozide, but not Two Other Growth Retardants, Modifies the Fate of Applied Gibberellin A9 in Chrysanthemum morifolium Ramat

Interactions between three growth retardants and gibberellinA₉ (GA₉) in Chrysanthemum morifolium Ramat. cv. Bright GoldenAnne grown in short days have revealed that the particular retardantemployed modifies the response to this gibberellin. When plants were given a foliar spray of daminozide (a substitutedsuccinamic acid), the effects of a subsequent application ofGA₉ to each lateral shoot, on both stem length and the rateof inflorescence development, were relatively small. However,GA₉ was highly active on plants previously sprayed with piproctanylbromide (a quaternary ammonium, piperidinium compound) or onthose given a compost drench of chlorphonium chloride (a quaternaryphosphonium retardant). In the absence of GA₉ all three retardantsreduced stem length and delayed flowering. Irrespective of the extent of the responses to various dosesof GA₉ (1–50 µg per shoot), a close relationshipwas maintained between internode extension and earliness offlowering, as in previous studies with retardants and othergibberellins. On plants which had received chlorphonium chlorideGA₃ and GA₁₃ were highly active and poorly active, respectively. The data suggest that daminozide could act as a retardant notonly by blocking the biosynthesis of gibberellins but also,wholly or partly, by restricting the metabolism or action ofendogenous gibberellins.     

Gibberellin-Dependent Root Elongation in Lactuca sativa: Recovery from Growth Retardant-Suppressed Elongation with Thickening by Low concentration of GA3

Higher concentrations of growth retardants, ancymidol and AMO-1718,were required to suppress root growth than hypocotyl growthin lettuce seedlings. Gibberellic acid (GA₃) counteracted theeffect of these growth retardants, but complete recovery ofroot growth was obtained only in a narrow range of growth retardantconcentrations. A much lower concentration of GA₃ (1 nM) wasneeded for recovery of root growth from ancymidol suppressionthan that for hypocotyl growth (100 (µM). GA₃ synergisticallypromoted root growth at moderate concentrations (10–100nM) with either ancymidol or AMO-1618. Ancymidol not only suppressed root elongation but also causedthickening of the elongation zone of the root, actions whichGA₃ completely canceled. Microscopic observation showed theseeffects were mainly due to the lateral expansion and shorteningof epidermal and cortical cells. Growth kinetics of roots recorded by a computer-regulated rhizometerindicated that the lag times of both growth suppression by ancymidoland growth recovery by GA₃ were about 4 h. -Naphthaleneacetic acid (NAA) did not counteract ancymidol suppressionof root and hypocotyl growth. These results support the concept that gibberellins play anindispensable role in root elongation at an extremely lowerconcentration than in hypocotyl elongation. (Received January 7, 1987; Accepted May 14, 1987)     

Invertase Activity, Carbohydrate Metabolism and Cell Expansion in the Stem of Phaseolus vulgaris L.

In the stem of Phaseolus vulgaris L. the specific activity ofacid invertase was highest in the most rapidly elongating internode.Activity of the enzyme was very low in internodes which hadcompleted their elongation, in young internodes before the onsetof rapid elongation, and in the apical bud. From shortly afterits emergence from the apical bud the elongation of internode3 was attributable mainly to cell expansion. Total and specificactivities of acid invertase in this internode rose to a maximumat the time of most rapid elongation and then declined. Transferof plants to complete darkness, or treatment of plants withgibberellic acid (GA₃), increased the rate of internode elongationand final internode length by stimulating cell expansion. Bothtreatments rapidly increased the total and specific activitiesof acid invertase in the responding internodes; peak activitiesof the enzyme occurred at the time of most rapid cell expansion. In light-grown plants, including those treated with GA₃, rapidcell and internode elongation and high specific activities ofacid invertase were associated with high concentrations of hexosesugar and low concentrations of sucrose. As cell growth ratesand invertase activities declined, the concentration of hexosefell and that of sucrose rose. In plants transferred to darkness,stimulated cell elongation was accompanied by a rapid decreasein hexose concentration and the disappearance of sucrose, indicatingrapid utilization of hexose. No sucrose was detected in theapical tissues of light-grown plants. The results are discussed in relation to the role of acid invertasein the provision of carbon substrates for cell growth. Key words: Cell expansion, Acid invertase, Hexose, Sucrose, Phaseolus     

Gibberellin-Growth Retardant Interactions on the Growth and Flowering of Clerodendrum thomsoniae

Gibberellin-growth retardant interactions on the vegetative growth and flowering of the vine Clerodendrum thomsoniae Balf. were studied using both exogenous treatments and biologically testing the acid fraction attained from the plant extract. The growth retardant, ancymidol, greatly retarded stem elongation and markedly increased flowering under inductive environments. Gibberellin A₃ (GA₃) application to the shoot tip stimulated vine growth, prevented flowering under inductive environments, and completely overcame ancymidol-induced effects. In contrast to GA₃, treatment with GA₇ had little effect on vegetative growth but increased flowering under inductive environments. The elevated activity of gibberellin-like compounds, as determined by bioassay, were similar except for a marked increase in levels in ancymidol-treated plants grown under inductive environmental conditions. Microscopic examination of the stem tip indicated that the action of the growth regulators involved the induction of floral buds. Thus, in Clerodendrum, ancymidol appears to stimulate an unknown gibberellin(s) and simultaneously acts antagonistically with GA₃.     

Gibberellin Regulation of Root Growth with Change in Galactose Content of Cell Walls in Pisum sativum

Root elongation of Alaska pea seedling was suppressed by higherconcentrations of growth retardants, CCC and ancymidol, thanthose required for shoot elongation. Gibberellic acid (GA³)led to recovery of ancymidol-inhibited elongation, with theconcentration (1 nM) required for roots being lower than thatfor shoots (10 µM). Ancymidol caused swelling of corticalcells in the elongating zone of the root, while GA³ completelycanceled this. These results suggest that roots require muchless gibberellin than shoots for normal elongation growth. Growth kinetics recorded by a computer-regulated rhizometerindicated that the lag periods for growth suppression by ancymidoland growth recovery by GA³ were about 10 h and 7 h, respectively. The composition of the cell wall sugars changed remarkably alongthe root axis from the tip to the base. The arabinose contentwas highest in the tip and rapidly decreased toward the base,whereas galactose complementarily increased toward the base.The thickened zone of ancymidol-treated roots had a higher galactosecontent than GA³-treated slender roots. Other neutral sugarswere not significantly influenced by ancymidol and/or GA³. Theseresults suggest that ancymidol makes cells short and thick withgalactose-rich cell walls while GA3 keeps cells extensible andslender with galactose-poor cell walls. (Received March 3, 1987; Accepted December 4, 1987)     

Internode Length in Pisum. A New Allele at the le Locus

In Pisum sativum L. a third, more severe, allele at the internodelength locus le is identified and named le^d. Plants homozygousfor le^d possess shorter internodes and appear relatively lessresponsive to GA₂₀ than comparable le (dwarf) plants. Gene le^dmay act by reducing the 3ß-hydroxylation of GA₂₀ tothe highly active GA₁ more effectively than does gene le. Theresults indicate that le is a leaky mutant and therefore thatendogenous GA₁ influences internode elongation in dwarf (le)plants. Pisum sativum, peas, internode length, genetics, gibberellin, dwarf elongation     

A Quantitative Study of Shoot Development in Vicia faba: II. The Elongation of Internode and Petiole

The elongation of the internodes and petioles of Vicia fabahas been studied in the plumules of normal seedlings, in seedlingsfrom which part or all of the cotyledonary reserve has beenremoved, and in axillary shoots developed on seedlings of variousages. The curves obtained by plotting the lengths of the internodesagainst their plastochrone ages reveal constant differencesin behaviour between plumules and axillary branches. As thegrowth of any shoot progresses a greater contribution to thetotal elongation rate cornea to be made by the internodes fartherremoved from the apex. The length of each internode depends throughout its developmenton its position in the stem as well as on the length of theinternode below. The extent to which the elongation of an internodelags behind that of the one below increases upwards, a relationshipsimilar to that previously shown to exist in respect of thevascularization of the internodes. In plumules the length of petiole corresponding to any givenlength of internode undergoes a decrease followed by an increaseas the plumule is traversed from base to apex, a relationshipexactly oppsite to that previously demonstrated between thevascularization of a leaf-trace bundle and that of the internodein which it runs. The effects of age and of removal of cotyledonary reserves aredescribed, and it is concluded that it is unlikely that thecharacteristic difference in internode length within the limitsof a single shoot are wholly due to changes in the availabiltyof reserve substances.     

Influence of growth retardants on the internode and ethylene production of sunflower plants

The growth-retarding activity of the norbornenodiazetine tetcyclacis and the di-oxanylalkenyl triazole LAB 150 978 as well as the ethylene-forming compounds 2-chloroethyl-phosphonic acid (ethephon) and 1-amino-cyclopropane-l-carboxylic acid (ACC) on stem histogenesis and ethylene production of sunflower plants ( He-lianthus annuus L. cv.Spanners Allzweck) has been studied. The shoot growth of plants hydroponically grown and treated was reduced by the compounds. The shortening in the length of the 1st internode caused by tetcyclacis and LAB 150 978 was mainly induced by inhibition of cell division (the internode possessed fewer cortical cells per cell file). In contrast, ethephon and ACC decreased internode elongation mainly by reducing the rate of cell enlargement.
The ethylene production of sunflower seedlings cultivated on agar nutrient medium rose with increasing concentrations of ethephon and ACC, the shoot length of the plants being progressively reduced.
Tetcyclacis and LAB 150 978 inhibited both the formation of ethylene and shoot growth. It is suggested that in contrast to ethephon and ACC, tetcyclacis and LAB 150 978 do not achieve their growth-retarding effect by influencing the production of ethylene.     

Effects of Ancymidol (a Growth Retardant) and Triarimol (a Fungicide) on the Growth, Sterols, and Gibberellins of Phaseolus vulgaris (L.)

The effect of the two substituted pyrimidines, ancymidol (a growth retardant) and triarimol (a fungicide) on Phaseolus vulgaris was studied. Both compounds retarded shoot and root elongation as well as increases in fresh weight. Both compounds caused production of ethylene-like responses when given in high dosages or when applied shortly after germination. As growth retardation was shown to occur in the absence of net increase in sterol levels, neither ancymidol nor triarimol apparently retards growth by inhibiting sterol synthesis.     

Apical Dominance Control in Ipomoea nil: The Influence of the Shoot Apex, Leaves and Stem

The outgrowth of lateral buds is known to be controlled by theupper shoot tissues, which include the apex, the young leavesand the upper stem. An analysis of the influence of these plantparts on axillary bud elongation in Ipomoea nil was carriedout by various treatments on these specific tissues. A restriction of elongation in the main shoot due to eitherdecapitation or shoot inversion resulted in the release of apicaldominance A non-linear type of compensating growth relationshipwas observed between the 13 cm apical growing region of thestem and the lateral buds. It was determined by decapitation,defoliation and AgNO₃ treatments that both the 13 cm stem-growthregion and the young leaves (1–5 cm in length) had a muchgreater inhibitory influence on the outgrowth of specified lateralbuds than did the stem apex (consisting of the terminal 0.5cm of the shoot). The specified lateral buds which were analyzedfor outgrowth were located a number of nodes below the shootapex. The intervening nodes were debudded. Although the importanceof young leaves in the control of apical dominance has beenpreviously recognized, the most significant result from thepresent study with Ipomoea was the strong influence of the 13cm apical growth region of the stem on the out growth of thelateral buds. Apical dominance, Ipomoea nil L., Pharbitis nil, growth region, lateral bud outgrowth, decapitation, defoliation, shoot inversion     

Comparative Effects of Ancymidol and Its Analogs on Growth of Peas and Ent-Kaurene Oxidation in Cell-Free Extracts of Immature Marah macrocarpus Endosperm

The plant growth retardant alpha-cyclopropyl-alpha-(4-methyoxyphenyl)-5-pyrimidine methyl alcohol (ancymidol) and a series of analogs of this substance in which one or more of the substituents were varied were tested for their comparative biological activity. The compounds were tested as inhibitors of internode elongation in peas and as inhibitors of the oxidation of ent-kaurene catalyzed by microsomal preparations from the liquid endosperm of Marah macrocarpus seeds. The relative effectiveness of a substance was generally the same as an inhibitor of the two processes. Ancymidol was the most effective. Substitution of the alcohol group of ancymidol by either methoxy or hydrogen groups reduced the activity only slightly. Substitution of the cyclopropyl group by an isopropyl moiety also had little effect on the activity. However, substitution of the cyclopropyl group with a phenyl or other aryl substituent greatly reduced the effectiveness of the analog as an inhibitor. Replacement of the 4-methoxyphenyl substituent with a similar substituent such as 4-chlorophenyl had little effect on activity, but replacement with a 2-methoxyphenyl group greatly reduced activity. Analogs in which the pyrimidyl moiety of ancymidol was modified were inactive in whole plants, but moderately active in the cell-free ent-kaurene oxidation system. The application of gibberellic acid can overcome the growth inhibitions due to treatment of the test plants with 10(-5)m or lower concentrations of the inhibitors. However, the inhibitory effects of 10(-4)m or higher concentrations of inhibitors on test plants were not overcome by the applications of exogenous gibberellic acid. These results support the idea that the effects of low concentrations of these substances on plant growth are primarily a consequence of their ability to inhibit ent-kaurene oxidation and gibberellin biosynthesis. Other modes of inhibition may operate at higher inhibitor concentrations.     

The Effect of Gibberellins on Growth and Flowering of Fragaria and Duchesnea

In a series of experiments petiole lengths were increased, steminternode elongation induced, runner formation promoted, andflower initiation inhibited both in the perpetual-fruiting andthe seasonal-fruiting varieties of strawberry by applicationsof gibberellic acid. Runners were induced to form in Fragariavesca semper-florcns var. Baron Solemacher, which does not normallyrunner. Thus the physiological processes which lead to the morphologicaldifferences between perpetual and seasonal fruiting types wereoverruled by treatment with gibberellic acid. Gibberellins A₁, A₄, A₇, and A₉, like gibberellic acid (A₃),induced elongation of petioles (a normal photoperiodic response),elongation of internodes on the main stem, and inhibition offlower formation in Baron Solemacher (responses not inducedby photoperiod). When applied to the cut stump of a debladed petiole, gibberellicacid inhibited flower formation at the growing apex of the stem,thus substituting for the leaf blade, which in long photoperiodsinhibited flower formation. A morphological study suggested that in Duchesnea indica, arelated genus, flower initiation is not regulated by environmentalcircumstances, but is the inevitable consequence of growth.Although promoting increase in petiole length and in elongationof lateral growths as in strawberry, gibberellic acid did notinhibit flower initiation in this species, except in so faras it caused a retardation in the growth of certain axillarybuds, so that a lower proportion of them reached the stage offlower initiation within the duration of the experiment. These results are discussed in relation to the hypothesis thatflower formation is regulated by an inhibitory hormone in seasonal-fruitingstrawberries.     

Effect of gibberellic acid on starch content of soybean (Glycine max L.) and its correlation with extension growth

This investigation was undertaken to study the effect of GA₃on extension growth of Glycine max L. and on starch contentof its individual internodes at maturity. The effect on hydrolyticactivity of the extract of different internodes was also studied.GA₃ stimulates the extension growth of stem by increasing theelongation of those internodes which are either in the processof elongation or being differentiated at the time of treatment.Starch content decreases with the position of the internode(from base upwards) on the intact plant. Corresponding internodeshave minimum starch content in 100 ppm GA₃-treated plants andmaximum in the controls. Internodes which show the maximum elongationdue to GA₃ treatment, show the least starch content and alsoshow maximum hydrolytic activity during the period of elongation.It is suggested that enhanced extension growth is brought aboutby enhanced mobilization of reserve food by GA₃. (Received November 21, 1967; )     

Changes in Endogenous Gibberellin and Auxin Activities during First Internode Elongation in Tulip Flower Stalk

Dark treatment during the most active period of tulip shootgrowth induced rapid elongation of the first internode. Endogenousfree-form gibberellin and diffusible auxin in the first internodeincreased while bound-form gibberellin decreased after the darktreatment. Alternating dark and light treatments at 24-h intervalscaused increases in elongation of the first internode and theamounts of free-form gibberellin and diffusible auxin in thedark but their decreases in the light. TIBA treatment at thefirst node inhibited both the elongation and the increase indiffusible auxin, but did not affect the gibberellin amount.Ancymidol application prior to the dark treatment inhibitedthe increase in both free-form gibberellin and diffusible auxin.Application of gibberellin A₃ increased both elongation of thefirst internode and the amount of diffusible auxin. It alsocaused recovery from ancymidol-mediated reduction in elongationand diffusible auxin content. Dark-induced elongation of thefirst internode was inhibited when all organs above the firstinternode were excised, but endogenous free-form gibberellinincreased and bound-form gibberellin decreased. After excision,elongation of the first internode occurred only when both GA₃and IAA were applied exogenously, or when IAA was applied withdark treatment. These results indicate that dark-induced elongationof the first internode of tulip is promoted by auxin, whichis transported from the upper organs into the first internodedue to stimulation from the dark-induced increase in free-formgibberellin. Free- and bound-form gibberellins changed complementarilywith the dark and light treatments. An interconversion systembetween the two forms in the first internode and its dependenceon light conditions are also discussed. (Received June 23, 1984; Accepted March 5, 1985)     

Inhibition of growth of microcultured <Emphasis Type="Italic">Hancornia speciosa</Emphasis> shoots by 3β-hydroxylated gibberellins and one of their C-3 deoxy precursors

Gibberellins (GAs) A(1), A(3), A(4) and A(7), all 3beta-hydroxylated, growth-active GAs, significantly inhibited shoot elongation and the formation of nodes in in vitro-grown Hancornia speciosa, as did GA(20), a 3-deoxy precursor of GA(1). Ancymidol, an early-stage inhibitor of GA biosynthesis, significantly retarded shoot elongation without affecting the formation of nodes. Co-application of ancymidol and GA(1 )did not overcome the ancymidol-induced growth retardation. Trinexapac-ethyl, which can inhibit 3beta-hydroxylation (GA activation) and 2beta-hydroxylation (GA inactivation), gave no significant response on either shoot elongation or node formation, while two isomers of 16,17-dihydro GA(5), also inhibitors of GA 3beta-hydroxylation, significantly inhibited both shoot growth and the formation of nodes. These unusual results may indicate a unique metabolism for GAs in microcultured shoots of H. speciosa.     

Factors Influencing the Distribution of Growth Between Stem and Axillary Buds in Decapitated Bean Plants

Phaseolus multiflorus plants at three stages of developmentwere decapitated either immediately below the apical bud orlower down at a point 1 cm above the insertion of the primaryleaves. Growth regulators in lanolin were applied to the cutstem surface. IAA always inhibited axillary bud elongation anddry-matter accumulation, and enhanced internode dry weight butnot elongation. GA₃ applied below the apical bud greatly increasedinternode elongation and dry weight, but simultaneously reducedbud elongation and dry-weight increase. Application of GA₃ 1cm above the buds had no effect on bud elongation in the youngestplants, but enhanced their elongation in the two older groups.IAA always antagonized GA₃-enhancement of internode extensiongrowth, whereas its effects on GA₃-enhanced dry-matter accumulationdepended on the stage of internode development. Bud elongationwas greater in plants treated with GA₃+IAA than in plants treatedonly with IAA, except in the youngest plants decapitated immediatelybelow the apical bud, where GA₃ caused a slight increase inIAA-induced bud inhibition. GA₃ increased inhibition of buddry weight by IAA in the two youngest groups of plants, butslightly reduced it in the oldest plants. No simple compensatorygrowth relationship existed between internode and buds. It wasconcluded that, (1) auxin appears to be the principal growthhormone concerned in correlative inhibition, and (2) availabilityof gibberellin to internode and buds is of importance as a modifyingfactor in auxin-regulated apical dominance by virtue of itslocal effects on growth in the internode and in the buds.     

Interaction of growth retardants,daylength, and gibberellins A19, A20, and A1 on shoot elongation in birch and alder

Gibberellins A₁₉, A₂₀, and A₁ were applied to seedlings of birch (Betula pubescens Ehrh.) and alder (Alnus glutinosa (L.) Gaertn.) in order to test their ability to counteract growth inhibition induced by growth retardants (ancymidol and BX-112) or short day (SD, 12 h) photoperiod. Ancymidol inhibits early and BX-112 inhibits late steps in gibberellin biosynthesis. BX-112 inhibited stem elongation in both species while ancymidol, applied as a soil drench, was effective in alder only. Growth retardants affected stem elongation mainly by inhibiting elongation of internodes. All three gibberellins were equally active when applied to seedlings treated with ancymidol; however, only GA₁ was able to counteract the growth inhibition induced by BX-112. SD-induced cessation of elongation growth in birch was counteracted by GA₁, and to some degree, by GA₂₀, while GA₁₉ was inactive. SD treatment did not induce cessation of apical growth in alder. These results are consistent with the hypothesis that of gibberellins belonging to the early C-13 hydroxylation pathway, GA₁ is the only active gibberellin for stem elongation.