Effects of Abscisic Acid on the Growth Pattern of the Shoot Apical Meristem and on Flowering in Chenopodium rubrum L.

Abscisic acid (ABA) at 1 x 10^–4 M or 3 x 10^–4 Mwas applied to the apical buds of Chenopodium rubrum plantsexposed to different photoperiodic treatments and showing differentpatterns of floral differentiation. Stimulation of growth inwidth of the apical meristem of the shoot and/or inhibitionof growth in length was obtained under all photoperiodic treatments.This change of growth pattern was followed by different effectson flowering. In non-induced plants grown under continuous light ABA stimulatedpericlinal divisions in the peripheral zone and the initiationof leaves as well as the growth in width of bud primordia. Inplants induced by two short days reduced growth of the meristemcoincided with ABA application. Longitudinal growth of the meristemwas inhibited in this case and only a temporary stimulationof inflorescence formation took place. In plants induced ata very early stage, ABA exerted a strong inhibitory effect onflowering. A permanent and reproducible stimulatory effect onflowering was obtained in plants induced by three sub-criticalphotoperiodic cycles if ABA was applied to apices released fromapical dominance. In this case formation of lateral organs andinternodes was promoted by ABA and was followed by stimulatedinflorescence formation. Gibberellic acid (GA2) at 1x 10^–4M or 3 x 10^–4 M brought about a similar effect on floweringas ABA, although the primary growth effect was different, i.e.GA₂ stimulated longitudinal growth. The effects of ABA and GA₂ on floral differentiation have beencompared with earlier results obtained from auxin and kinetinapplications. These growth hormones are believed to regulateflowering by changing cellular growth within the shoot apex.Depending on the actual state of the meristem identical growthresponses may result in different patterns of organogenesisand even in opposite effects on flowering. Shoot apex, flowering, photoperiodic induction, abscisic acid, gibberellic acid, Chenopodium rubrum L.     

Regulation of lettuce hypocotyl elongation by gibberellic acid. Correlation between cell elongation, stress-relaxation properties of the cell wall and wall polysaccharide content

Lettuce hypocotyl elongation caused by gibberellic acid wasstrongly inhibited by coumarin and dichlobenil, known inhibitorsof cellulose biosyndiesis. Stress-relaxation analysis of thecell wall revealed that gibberellic acid induces a decreasein both minimum relaxation time (To) and relaxation rate (b)and an increase in maximum relaxation time (Tm), when gibberellicacid stimulates hypocotyl elongation. Both coumarin and dichlobenilnullified the effect of gibberellic acid on changes in To, Tmand b values. The content of pectic, hemicellulosic and cellulosic substancesin the cell wall increased per hypocotyl but decreased per unithypocotyl length, in response to gibberellic acid treatment.Particularly, gibberellic acid caused a substantial increasein cellulose content per hypocotyl but a decrease per unit length.A good correlation existed between the decrease in To and thedecrease in hemicellulose content per unit lengdi of the cellwall. The increase in Tm was correlated with the decrease incellulose content per unit length of the cell wall. The decreasein b was correlated with the decrease in the content of bothcellulose and hemicellulose per unit length. Based on these results, we discuss the role of polysaccharidemetabolism of the cell wall in gibberellic acid-induced lettucehypocotyl elongation and the nature of gibberellic acid-inducedbiochemical modifications of the cell wall, which are representedby changes in stress-relaxation properties of the cell wall. ¹Present address: Department of Anatomy, Aichi Medical University,Nagakutecho, Aichigun, Aichi 480-11, Japan. (Received September 22, 1975; )     

Studies on the physiology of hyacinth bulbs (Hyacinthus orientalis L.) the effect of plant growth regulators on metabolic activities in non-chilled hyacinth bulbs

The effect of gibberellic acid, benzyladenine and a mixture of these compounds on the activity of some hydrolytic enzymes was studied in hyacinth bulbs non-exposed to low temperatures. Plant growth regulators were applied on the heel of dormant bulbs in the middle of July. An intensive elongation of the inflorescence was observed only in the plants treated previously with GA₃ and grown in a warm greenhouse for 63 and 84 days. The activities of amylase, invertase and acid phosphatase were higher in the flower buds of unrooted bulbs treated with growth regulators than in the control plants, although growth regulators did not affect the level of extractable proteins. The elongation of the inflorescence in the plants treated with gibberellic acid was correlated with a sharp increase of invertase activity in this organ. The effect of GA₃ and BA on the activity of other enzymes in buds and scales varied with the period of plant growth.     

Vegetable Plant Part Relationships. IV. An Interpretation of Growth Regulator Experiments with Root Crops

A quantitative scheme to describe the growth of plant partsduring the vegetative phase of development is extended to includethe concept of hormone directed transport. The expected effecton shoot/storage root d. wt relationships of a single àxternalapplication of a growth regulating chemical is investigatedusing this approach. The theory predicts that the resultingchange in the pattern of assimilate partitioning will modifythe underlying relationship between shoot and storage root weightsin a simple measurable fashion. The theory is inevitably oversimplifiedand speculative in parts but when a derived equation was fittedto data from an experiment in which gibberellic acid and daminozidewere applied to carrots, close agreement was found between thepredictions and experimental data. Daucus carota, carrot, shoot weight, root weight, gibberellic acid, N-dimethylamino-succinamic acid (daminozide), growth analysis     

Laticifer Differentiation in Hevea brasiliensis: Induction by Exogenous Jasmonic Acid and Linolenic Acid

Laticifer differentiation of Hevea brasiliensis was investigatedby application of lanolin containing jasmonic acid (JA) or otherchemicals to the surface of young stems in epicormic shoots.The young stems had primary laticifers and no secondary laticifers.When applied to extending young stems, JA led to a significantincrease in primary laticifer number but did not induce secondarylaticifer differentiation. Secondary laticifer differentiationand a less significant increase in primary laticifer numberwere caused by JA application to the extended young stems. Theinduction of the secondary laticifers was dependent on the concentrationof JA applied. Cambium cell division leading to the formationof secondary phloem was not accelerated by JA treatment. Treatedbark tissues showed no visible changes except for the additionallaticifers, which were normal in ultrastructure. The secondarylaticifers were also induced by the application of linolenicacid, a precursor of JA biosynthesis. Abscisic acid, ethephonand salicylic acid had no detectable effect on laticifer differentiation.Copyright 2000 Annals of Botany Company Hevea brasiliensis, laticifer differentiation, jasmonic acid, linolenic acid, vascular cambium.     

In vitro Growth of Vegetative Tomato Shoot Apices

Explants from the shoot apex of the tomato, comprising the apicaldome and youngest primordium together with small amounts ofsub-apical tissue were cultured for periods of 1 to 4 plastochrons.By the use of a simple parameter, the axillary distance, thegrowth-rate could be accurately monitored throughout each plastochron. Gibberellic acid, coconut milk, and kinetin, in addition tosucrose and inorganic salts, all promoted growth of the apex;a combination of gibberellic acid and coconut milk gave thefastest growth. Temperature had a large effect on the growth-ratewith an in vitro Q₁₀ of 2.1 contrasted with an in vivo Q₁₀ of1.2 over the range of 15 to 25 ?C. On gibberellic acid and coconutmilk at 15 ?C two-thirds of the in vivo growth--rate was sustainedin culture for two plastochrons after which the growth-rategradually declined; at 20 and 25 ?C growth-rates slightly higherthan in vivo rates were sustained for 1 plastochron before amore rapid decline. The anatomy of these in vitro apices wasnormal for 1? plastochrons after which there were small increasesin cell volume in the developing primordium. Reducing the amount of sub-apical tissue drastically reducedthe growth rate but had little effect on the responses to gibberellicacid and coconut milk. Explants are considered to be useful material for studying thechanges that take place in the apex during the course of 1 or2 plastochrons, but inadequate on the media tested for experimentsinvolving longer periods of growth. Explants also provide asensitive assay system for the effects of growth factors onthe rate of shoot apical growth.     

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.     

Regulation of Floral Initiation and Development in an Orchid Hybrid Aranda Deborah

The effects of growth regulators on floral initiation and developmentin a monopodial orchid hybrid. Aranda deborah, were studied.Auxin, gibberellic acid and abscisic acid did not stimulateany floral initiation. Auxin antagonists and growth retardantsstimulated floral initiation but many of the initiated budsdid not continue to develop to maturity. Cytokinin (6-benzylaminopurine)stimulated not only bud initiation but also floral developmentto maturity. A distinction was made between the process of floral initiationand floral development. It was suggested that both these processeswere regulated by the correlative apical dominance effect.     

Invertase Activity, Soluble Carbohydrates and Inflorescence Development in the Tomato (Lycopersicon esculentum Mill.)

The concentration of reducing sugars in the developing firstinflorescence of the tomato (Lycopersicon esculentum Mill.)increased steadily between the macroscopic appearance of theflower buds and the initial stages of fruit expansion. Overthis period sucrose concentrations remained relatively constant.The rise in reducing sugar concentration was accompanied byan increase in the activity of an acid invertase. In individualflower buds invertase activity rose to a maximum shortly beforeanthesis and declined sharply as the anthers dehisced. Increased planting densities and removal of source leaves reducedthe rate of dry matter accumulation by the first inflorescenceand increased the incidence of flower bud abortion. These changeswere correlated with reductions in reducing sugar concentrations,in reducing sugar/sucrose ratios and in acid invertase levels.Removal of young leaves at the shoot apex significantly increasedthe relative growth rate of the inflorescence and led to a substantialincrease in its invertase content. These treatments had relativelylittle effect on sucrose concentration in the inflorescence. The data are consistent with the operation of an invertase-mediatedunloading mechanism for transported sucrose at sinks in theflower buds. It is suggested that the retarded development ofthe first inflorescence and the high incidence of flower budabortion observed under conditions of reduced photoassimilateavailability are causally related to the decline in invertaseproduction in the flower buds. Possible mechanisms for the regulationof invertase synthesis in the flowers are discussed. Lycopersicon esculentum Mill, tomato, inflorescence development, invertase, sink activity     

Requirement of sodium chloride for the action of gibberellic acid in stimulating hypocotyl elongation of a halophyte, Salicornia herbacea L.

NaCl stimulated hypocotyl elongation of the halophyte Salicorniaherbacea L. grown either in light or dark. Its optimal concentrationwas around 0.1–0.2 M and its promoting effect was muchmore prominent in the dark. Gibberellic acid at 10^–5 Mstimulated hypocotyl elongation in light but not in the dark.Indole-3-acetic acid and kinetin were ineffective in promotinghypocotyl elongation. In light, gibberellic acid and NaCl synergisticallyenhanced hypocotyl elongation when both were given simultaneously.The action of NaCl could be replaced by KCl, but not by mannitol.Osmotic pressure of the epidermis of the Salicornia hypocotylincreased in response to gibberellic acid and/or NaCl treatment.Na⁺ content in the hypocotyl increased with NaCl application.Gibberellic acid and NaCl when given alone increased the extensibilityof the hypocotyl cell wall. Synergistic interaction in increasingthe extensibility was observed between gibberellic acid andNaCl. Stress-relaxation analysis of mechanical properties ofthe hypocotyl wall revealed that gibberellic acid and NaCl actedsynergistically in decreasing minimum relaxation time. Basedon these results, a possible mechanism by which gibberellicacid and NaCl regulate hypocotyl elongation of Salicornia herbaceaL., a typical halophilic plant, is discussed. ¹ Present address: Laboratory of Biology, Tezukayama College,Gakuen Minami, Nara 631, Japan. (Received June 13, 1978; )     

Specificity of Gibberellin and Sucrose-promoted Flower Bud Growth in Gladiolus

A critical stage in flower bud growth in the spike of Gladioluswhich is initiated by gibberellic acid (GA₃) and sustained bysucrose has been identified. This corresponds to the stage atwhich separation of the outer bract occurs. In buds at differentdevelopmental stages isolated and held in water, it is the samebud stage that first shows increased growth. Buds not inducedby light were shown to respond more significantly to GA₃ andsucrose than those induced by light. Since the separation ofthe outer bract results in light-induced amylase productionand starch hydrolysis leading to petal growth, it is proposedthat growth promotion by GA₃ is related to light-induced petalgrowth at this specific stage. flower bud growth, Gladiolus natalensis, gibberellic acid, sucrose     

The influence of gibberellic acid and abscisic acid on cell and tissue differentiation of bean callus.

Bean callus was induced to form roots (tissue differentiation) and vascular nodules (cell differentiation) by lowering the ratio of auxin to cytokinin in the growth medium. Both types of differentiation were inhibited by the addition of abscisic acid (at concentrations greater than I muM) to induction medium. Initiation of differentiation was inhibited, but its subsequent development was not, and the inhibition was not affected by the addition of gibberellic acid. Addition of gibberellic acid (GA) alone to induction medium stimulated tissue differentiation, although cell differentiation was unaffected (30 muM GA) or inhibited (45 muM GA) and its onset was delayed at both concentrations. Root initiation was also stimulated by gibberellic acid (0.I-45 muM) at an auxin-to-kinin ratio 10 times that normally optimal for cell differentiation. The phenylalanine ammonia lyase (PAL) activity of the calluses was closely correlated with the amount of cell differentiation which had occurred, and measurement of this confirmed that gibberellic acid delayed the initiation of cell differentiation. The increase and subsequent decline of PAL and betaI leads to 3 glucan synthetase activities, normally induced by transfer to induction medium, was abolished by abscisic acid. Addition of gibberellic acid did not affect the betaI leads to 3 glucan synthetase activity.     

Runner Formation in Everbearing Strawberry as Influenced by Growth-Promoting and Inhibiting Substances

The interactive effects of gibberellic acid, abscisic acid,and benzyladenine were studied in relation to runner formationof the everbearing strawberry. In two of three cultivars studied,Ozark Beauty and Superfection, exogenous gibberellic acid stimulatedrunner formation and inhibited flowering. In the Geneva cultivar,a shy runner producer, gibberellic acid application as a foliarspray failed to induce runners. When applied in combinationwith benzyladenine, gibberellic acid greatly stimulated runnerformation Benzyladenine alone had no effect on runnering. Exogenous abscisic acid inhibited petiole length and runnerformation and had no influence on the number of inflorescencesinitiated. Response to exogenous gibberellic acid or abscisicacid varied according to the reproductive or vegetative stagethe plant exhibited at the time of treatment. Activity of endogenous gibberellin-like substances was not substantiallydifferent between flowering and non-flowering field-grown Genevaplants when sampled in long day lengths of August. Endogenousinhibitors were highly active in flowering Geneva plants andrelatively inactive in non-flowering plants The implications of these findings on hormonal balance in thestrawberry are discussed.     

Water Deficit and Inflorescence Development in Zea mays L.--The Role of the Developing Tassel

In the normal pattern of development of Zea mays (cv. Iochief)a single mature female inflorescence is produced at node 7.A brief episode of water deficit at the time of terminal maleinflorescence initiation induced the subsequent developmentof two to three mature female inflorescences at nodes 5–7.This growth of the inflorescences at lower nodes was accompaniedby a marked inhibition of the growth of the terminal male inflorescence.Removal of either the developing terminal inflorescence or ofthe axillary inflorescence at node 7 at this time also promotedthe growth of the lower axillary inflorescences. The growthof these inflorescences was further stimulated by a period ofwater deficit when only the inflorescence at node 7 was removed,but removal of the male inflorescence abolished the capacityof these inflorescences to respond to the water deficit Excisionof the male inflorescence immediately before or immediatelyafter the period of water deficit produced the same response.It is concluded that this response of the lower axillary inflorescencesto water deficit is mediated through an effect on the developingterminal male inflorescence. Zea mays, water deficit, inflorescence development, tassel, correlative inhibition     

The Role of Roots in Control of Bean Shoot Growth

Restriction of root growth by growing bean plants (Phaseolusvulgaris L.) in very small pots led to the development of dwarfplants. The leaves of those plants were smaller and their internodesshorter than those of control plants which were grown in largerpots and had developed a more extensive root system. A largequantity of starch—much more than in control plants —accumulated in the leaves and shoots of the dwarf plants. Increasingthe amount of minerals which was supplied to the roots, enhancedleaf growth of the control plants but failed to affect the dwarfones, in spite of the fact that in both cases the treatmentincreased the content of N, P and K in all the plant organs.The leaf water content was similar in both treatments, but theleaf water potential was higher in the dwarf plants. Exogenousapplication of gibberellic acid (GA₃) to the dwarf plants overcamethe reduction of stem growth completely, and that of the leavespartially. Application of the cytokinin, benzyladenine (BA)did not affect stem growth, but increased that of the primaryleaves. A combined supply of GA₂ + BA restored completely thegrowth of the stem and the primary leaves, and partially thatof the trifoliate leaves. It is concluded that a limited rootsystem restricts shoot growth through an hormonal system inwhich at least gibberellins and cytokinins are involved, andthat the dwarfing is not a consequence of mineral or assimilatedeficiency, or due to water stress. Phaseolus vulgaris L., leaf growth, stem growth, root restriction, gibberellic acid, benzyladenine, cytokinin     

Effects of Temperature and Growth Regulators on Formation of Anlagen, Tendrils and Inflorescences in Vitis vinifera L.

The effects of single, combined and sequential application ofgibberellic acid (GA), chlormequat and cytokinins on the formationof anlagen, tendrils and inflorescences were studied in grapevines(cv. Muscat of Alexandria) grown with natural illumination athigh temperature (30 °C day to 25 °C night) and at lowtemperature (21 °C day to 16°C night or 18 °C dayto 13 °C night). GA promoted the formation of anlagen andgrowth of tendrils regardless of temperature, but inhibitedinflorescence production. Chlormequat had the opposite effecton anlagen formation and tendril growth and promoted inflorescenceformation from pre-formed anlagen or from tendril initials.While low temperature is normally unfavourable for inflorescenceformation, this was induced by chlormequat even at low temperature,but only with summer light conditions. Cytokinin application to plants pre-treated with chiormequatcaused tendrils to grow into inflorescences regardless of temperatureregimes. Moreover, shoot primordia were also formed in place⁸oftendrils in cytokinin treated plants even without chlormequatpre-treatment. Vitis vinifera L., grapevine, gibberellic acid, chlormequat, cytokinins, benzyladenine, inflorescence, tendrils     

Growth and Graviresponsiveness of Primary Roots of Zea mays Seedlings Deficient in Abscisic Acid and Gibberellic Acid

Moore, R. and Dickey, K. 1985. Growth and graviresponsivenessof primary roots of Zea mays seedlings deficient in abscisicacid and gibberellic acid.—J. exp. Bot. 36: 1793–1798. The objective of this research was to determine if gibberellicacid (GA) and/or abscisic acid (ABA) are necessary for graviresponsivenessby primary roots of Zea mays. To accomplish this objective wemeasured the growth and graviresponsiveness of primary rootsof seedlings in which the synthesis of ABA and GA was inhibitedcollectively and individually by genetic and chemical means.Roots of seedlings treated with Fluridone (an inhibitor of ABAbiosynthesis) and Ancymidol (an inhibitor of GA biosynthesis)were characterized by slower growth rates but not significantlydifferent gravicurvatures as compared to untreated controls.Gravicurvatures of primary roots of d-5 mutants (having undetectablelevels of GA) and vp-9 mutants (having undetectable levels ofABA) were not significantly different from those of wild-typeseedlings. Roots of seedlings in which the biosynthesis of ABAand GA was collectively inhibited were characterized by gravicurvaturesnot significantly different from those of controls. These results(1) indicate that drastic reductions in the amount of ABA andGA in Z. mays seedlings do not significantly alter root graviresponsiveness,(2) suggest that neither ABA nor GA is necessary for root gravicurvature,and (3) indicate that root gravicurvature is not necessarilyproportional to root elongation. Key words: Abscisic acid, Ancymidol, Fluridone, gibberellic acid, root gravitropism, Zea mays     

Requirement of cotyledons for gibberellic acid-induced hypocotyl elongation in lettuce seedlings. Isolation of the cotyledon factor active in enhancing the effect of gibberellic acid

The role of cotyledons in hypocotyl elongation caused by gibberellicacid was studied using young seedlings of lettuce, Lactuca saliva,var. ‘Grand Rapids’. Removal of cotyledons fromintact seedlings resulted in a depression of hypocotyl elongationcaused by gibberellic acid. Gibberellic acid-induced hypocotylelongation in decotylized seedlings, was however, substantiallyenhanced by incubating the seedlings together with excised cotyledons.The exudate from excised cotyledons also enhanced the effectof gibberellic acid on hypocotyl elongation in decotylized seedlings.This active principle (named the cotyledon factor) in the cotyledonexudate was stable against heating at 100?C for 15 min, permeatedthe dialysis membrane, and was extractable with ethyl acetate.Biological activity of the cotyledon factor was not replacedby indole-3-acetic acid, kinetin, cyclic AMP, vitamins, sucroseor inorganic nutrients. The biological significance of the cotyledonfactor is discussed in relation to the action of gibberellicacid. (Received February 14, 1973; )     

Factors Affecting Shedding of Flowers in Soybean (Glycine max (L.) Merrill)

Flower shedding in soybean, Glycine max (L.) Merrill, was studiedusing cultivar ‘Clark’, isoline E₁t, which has relativelylong racemes for convenient identification and observation ofindividual flowers. On each raceme studied, pod set was greatestat the proximal (basal) positions, whereas shedding was greatestat the most distal positions. When proximal flowers were removedas they reached anthesis, pod set increased at the more distalpositions. Pod set was increased in some instances by applicationof water directly to the ovaries as a drop in the calyx cup.Peroxidase activity changed in parallel with ovary development,increasing rapidly in growing pods but not in shedding flowers.Increases in flower peroxidase was mainly in ovary walls. Flowerstaken at or near anthesis from positions with high percent podset could be grown in vitro with especially good ovary enlargement,whereas ovaries in flowers taken from positions of low pod setdid not enlarge in culture. Unidentified substances were extracted from young pods which,when incorporated into lanolin and tested in an in situ bioassay,could mimic the effect of proximal flowers in inducing sheddingof distal flowers. Indole-3-acetic acid resembled the extractedmaterials in inducing shedding, but differed by eliciting side-effectsthat extracts did not. The growth substances abscisic acid,gibberellic acid, and benzyladenine did not promote sheddingin the in situ test. The evidence was taken to indicate that soybean flower sheddingis induced in distal flowers by substances from the more proximal,fertilized ovaries, and that this is possibly due to interferencewith some of the intense metabolic changes that follow pollinationand fertilization.     

Abscisic Acid and Apical Dominance in Phaseolus coccineus L. The Role of Tissue Age

Abscisic acid (ABA) applied to the decapitated second internodeof runner bean plants enhanced outgrowth of lateral buds onlywhen internode stumps were no longer elongating. Applied toelongating internodes of slightly younger plants, ABA causesinhibition of bud outgrowth. Together with 10^–4 M indol-3-ylacetic acid (IAA), ABA stimulated internode elongation and interactedadditively in the inhibition of bud outgrowth. A mixture of10^–5 M ABA and 10^–6 M gibberellic acid (GA₃ ) causedsimilar effects on internode growth as IAA + ABA, but was mutuallyantagonistic in effect on growth of the lateral buds. Abscisic acid, apical dominance, gibberellic acid, indol-3yl acetic acid, Phaseolus coccineus, bean