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; )     

In vitro Responses of Embryoids ofEschscholzia californica

Thein vitro embryoids ofEschscholzia californica do not form normal plantlets in cultures. However, 6-benzylaminopurine and gibberellic acid, when added to the medium, partially alleviate this inhibition. Experiments involving decotylization, and culture of embryoids at different stages, indicated the cardinal role of cotyledons in plumular growth.     

Co-regulation Of ear growth and internode elongation in corn

Ear is the harvest part of corn (Zea mays L.) and we are interested in studying its growth and development in our effort in corn yield improvement. In our current study, we examined the relationship between ear growth and internode characteristics using different approaches. Correlations between stem growth rate and number of ears per plant (prolificacy) were assessed among several genotypes. Internode elongation of 2 genotypes was modified by plant hormones and by population density manipulations. Among the 7 genotypes examined that have different prolificacy levels, there was a general correlation of slower stem elongation at middle growth stages and larger ear number. When the internode elongation was enhanced by application of gibberellic acid (GA), ear growth was suppressed; and when a GA synthesis inhibitor uniconazole was applied at early stages, internode length was reduced and ear growth was promoted in terms of both ear size and visible ear number at silking stage. Higher population density caused longer internodes and fewer ears per plant and the effect of lower density was the opposite. Our results suggested that internode elongation in the middle section of corn plants was linked to suppression of ear development in corn.     

Growth and osmoregulation in Pisum sativum subhooks as affected by gibberellic acid and cotyledon excision

Growth stimulation by gibberellic acid (GA) of the Alaska pea ( Pisum sativum L.) subhook was observed within 6 h after its application; the stimulation being larger in cuttings with cotyledons than in decotylized ones. The osmotic potential in the subhook increased as it grew, the rate of its increase being faster in cuttings without than in cuttings with cotyledons. GA had no effect on the change in the osmotic potential until 8 h after GA application, but afterwards it suppressed the increase in cuttings with cotyledons. This GA effect was not observed in decotylized cuttings. Changes in the osmotic potential were well correlated with changes in the concentration of soluble sugars, but not with changes in amino acids and K⁺, Soluble sugars accumulated in the subhook of cuttings with and without cotyledons in proportion to growth, irrespective of the presence or absence of GA. Cotyledon excision suppressed sugar accumulation, and GA promoted it in cuttings with cotyledons but not in decotylized ones. These results suggest that GA stimulates the translocation of sugars from the cotyledons to the subhook and, thereby, maintains the osmotic potential low, resulting in enhanced growth.     

Osmoregulation in hypocotyls of etiolated mung bean seedlings with or without cotyledons in response to water-deficient stress

Effects of water-deficient stress and cotyledon excision on osmoregulation in hypocotyls of dark-grown mung bean seedlings were studied, and following results were obtained. Water-deficient stress inhibited hypocotyl elongation either in intact or decotylized seedlings. The inhibition was more conspicuous in decotylized seedlings than in intact ones. Water-deficient stress decreased osmotic potential in hypocotyls, while cotyledon excision increased it. The concentrations of soluble sugars, free amino acids and potassium ions in hypocotyls of intact or decotylized seedlings increased in response to water-deficient stress. Cotyledon excision reduced the concentration of soluble sugars and free amino acids, but it did not change the concentration of potassium ions, suggesting that a part of soluble sugars and free amino acids is transported from cotyledons. Unlike cotyledon excision, excision of the apex or roots had no influence on osmoregulation in response to water-deficient stress. Segments excised from hypocotyls had the ability to osmoregulate in response to water-deficient stress. Based on these results, the role of cotyledons in osmoregulation in response to water-deficient stress and quantitative relationships between osmotic potential and hypocotyl elongation in etiolated mung bean seedlings are discussed.     

Isolation and chemical identification of a lettuce cotyledon factor, a synergist of the gibberellin action in inducing lettuce hypocotyl elongation

Removal of cotyledons from intact lettuce seedlings retardedhypocotyle elongation caused by gibberellic acid. This inhibitoryeffect of cotyledon excision was alleviated by incubating decotylizedseedlings with a hot water extarct from excised cotyledons orintact seedlings. This active principle was identified as dihydroconiferylalcohol on the basis of its IR, NMR and mass spectra. (Received August 28, 1973; )     

Differences in Endogenous Levels of Gibberellin-Like Substances in Nodules of Phaseolus lunatus L. Plants Inoculated with Two Rhizobium Strains

Lima bean plants (Phaseolus lunatus L.) inoculated with Rhizobium sp. strain 127E14, which lacks constitutive nitrate reductase activity, were significantly taller after 4 weeks of age than plants inoculated with strain 127E15, which contains constitutive nitrate reductase activity. Plants inoculated with either strain responded to application of 5 micrograms gibberellic acid per plant with rapid internode elongation; plants inoculated with strain 127E15 became less responsive to gibberellic acid from 3 to 5 weeks of age, while plants inoculated with strain 127E14 did not. The height of plants inoculated with strain 127E14 was reduced by 20% with application of gibberellin biosynthesis inhibitors to the roots, while height of plants inoculated with strain 127E15 was unaffected.     

Effects of gibberellic Acid and sucrose on the growth of oat (Avena) stem segments

Gibberellic acid induced growth in Avena (oat) stem segments within 35 minutes after hormone application. The total elongation elicited by gibberellic acid was greater than 15 times the control growth. The sensitivity of the segments to low concentrations of gibberellic acid (1 pmole) and the specificity of the segments to the gibberellin class of hormones suggest that oat stem segments would be a valuable tool for gibberellin bioassays. Both gibberellic acid-induced growth and control growth are temperature-dependent and showed a Q₁₀ of two or greater. Although the most apparent effect of gibberellic acid was to promote the uptake of water into the internode, the hormone also promoted transport of endogenous substrate and the uptake of exogenous substrate into the growing region. The growth promotion was accomplished without an apparent increase in osmotic pressure.     

蒺藜苜蓿株高控制基因COSTIN的克隆及功能研究

株高是影响植物株型建成的重要农艺性状之一,直接决定作物的倒伏性和生物产量,但目前关于苜蓿等豆科牧草株高性状形成的分子调控机制尚不清楚。通过定向筛选豆科模式植物蒺藜苜蓿Tnt1逆转座子插入突变体库,分离鉴定了一个蒺藜苜蓿矮化突变体compact stalk internodes(costin),该突变体的矮化表型是由于茎节伸长受到抑制所致。通过基因表型连锁分析成功克隆了COSTIN基因,该基因编码一个钙离子交换蛋白,与拟南芥的CALCIUM EXCHANGER 7(CAX7) 基因高度同源。qRT-PCR检测发现COSTIN基因在茎、叶和果荚等组织中有较高的表达。进一步研究发现在costin突变体中赤霉素合成途径关键基因MtCPS、MtKAO1、MtGA20ox4、MtGA20ox7和MtGA3ox1表达下调;外施赤霉素GA3可以恢复costin突变体的矮化表型。上述研究表明COSTIN基因通过影响植物激素赤霉素的生物合成来调控蒺藜苜蓿的茎节伸长。     

The regulation of cambial division and secondary xylem differentiation in xanthium by auxins and gibberellin

Cambial division continued in decapitated Xanthium plants without concomitant xylem fiber differentiation. The application of indoleacetic acid to these plants did not affect the production of cambial derivatives or induce xylem fiber differentiation. When naphthaleneacetic acid was applied either to the second internode or to the stump of a lateral shoot, xylem fiber differentiation was induced in the newly formed cambial derivatives on the xylem side of the cambium in the stem. When naphthaleneacetic acid was applied unilaterally, xylem fiber differentiation was restricted to that side of the stem in the first internode and hypocotyl. Naphthaleneacetic acid also enhanced the production of cambial derivatives. Gibberellic acid enhanced cambial derivative production but did not affect the differentiation of xylem fibers. Similar numbers of cambial derivatives were produced in some naphthaleneacetic acid-treated plants in which xylem fiber differentiation was induced and in gibberellic acid-treated plants which did not differentiate xylem. When naphthaleneacetic acid was applied 72 hours after decapitation, the oldest of the cambial derivatives on the xylem side failed to develop into fibers although younger cells did. These results suggest that auxin has its direct effect on the induction of xylem differentiation rather than the induction of divisions prerequisite to differentiation.     

THE DEVELOPMENTAL MORPHOLOGY OF NICOTIANA TABACUM ‘WHITE BURLEY’ AS INFLUENCED BY VIRUS INFECTION AND GIBBERELLIC ACID

Stein , Diana B. (U. Montana, Missoula.) The developmental morphology of Nicotiana tabacum ‘White Burley’ as influenced by virus infection and gibberellic acid. Amer. Jour. Bot. 49(5): 437–443. Illus. 1962.—‘White Burley’ tobacco with Severe Etch Virus (SEV) displayed a reduction of plant height which was overcome to a limited degree by spraying with gibberellic acid (GA). Spraying with GA, while hastening maturity in terms of earlier elongation and flowering, also prolonged the life of treated plants. Infection with SEV caused an increased rate of leaf production, and since flowering was also delayed, the greater number of leaves is produced by infected plants. Spraying with GA also increased the rate of leaf production but did not increase the final number of leaves produced. All groups except the unsprayed virus-infected plants showed a spurt in leaf production just prior to flowering. The pattern of internode elongation was obtained by the periodic measurement of individual internodes. In general, this pattern reflected the stunting properties of the virus and the growth-promoting properties of the GA. Internodes which were mature at time of spraying with GA were not affected. Infection with virus generally delayed elongation and shifted the internode pattern. Infection with SEV tended to reduce the size of leaves already present prior to inoculation, but some leaves produced after infection were actually 1arger than the same leaves on the controls. Spraying a healthy plant with GA made older leaves longer and wider, while less mature leaves at time of treatment tended to be longer and narrower. Spraying with GA reversed the reduction in size caused by the virus only if the leaf was a very young primordium or was formed during the course of treatment with GA.     

Ethylene-induced Tropism of Trifolium fragiferum L. Stolons

The hypothesis that ethylene regulates prostrate stem growth was investigated using stolons of strawberry clover (Trifolium fragiferum L. var. Salina). Stolons became erect when treated with ethylene or 2-chloroethylphosphonic acid. Curvature was visibly detectable 2 hours after ethylene treatment, and subsequent stem elongation was rapid. Indoleacetic acid application to prostrate stolons caused only a small transitory curvature persisting less than 48 hours. Indoleacetic acid-stimulated curvature was accompanied by an increase in ethylene evolution. When stolon curvature was induced by placing strawberry clover plants in darkness or by applying gibberellic acid, ethylene production did not parallel stolon curvature.     

The Effect of Single and Repeated Gibberellic Acid Treatment on Internode Number and Length in Dwarf Peas

In long-term experiments comparing the results of single and repeated treatment of dwarf peas with gibberellic acid, both once-treated and weekly-treated plants formed more internodes than control plants. The initial high rate of internode formation in the once-treated peas dropped rapidly reaching that of control plants three weeks after treatment. Weekly-treated plants maintained a higher rate of internode formation. The ratio of internode lengths of once-treated plants to control plants was high (over 3) for the internodes which were elongating during or shortly after the single treatment but dropped rapidly and approached unity in later-developed internodes. The ratio of internode lengths of weekly-treated plants to control plants continued to be high throughout the experiment.     

Essai de remplacement de la réfrigération vernalisante par des applications d’acide gibbérellique chez la jusquiame noire bisannuelle (hyoscyamus niger L.)

Applications of various amounts of GA₃ onto the shoot apex of biennial rosette-plantHyoscyamus niger L., exposed to long days and non vernalized, caused internodes formation and stem elongation. The stem length was proportional to the amount of GA₃ applied. Number and length of developed internodes and the whole length of the shoot were maximal in plants treated with a greater amount of GA₃. In the end, stem elongation stopped and plants formed perchedrosettes without flowering. Hence, gibberellic acid participates in mechanisms of flowering only by indirect effect on stem elongation and not directly on flower formation itself.     

Proserpinaca: photoperiodic and chemical differentiation of leaf development and flowering

Proserpinaca palustris L. produced juvenile leaves on 8-hour photoperiods, adult leaves on 12-hour photoperiods, and adult leaves and flowers on 14-hour photoperiods. Treatment of plants growing on 8- and 14-hour photoperiods with gibberellic acid caused stem elongation and inhibited flowering. The treated plants on 8-hour photoperiods produced adult-like leaves.     

Control of Internode Length in Pisum sativum (Further Evidence for the Involvement of Indole-3-Acetic Acid)

The effects of altered endogenous indole-3-acetic (IAA) levels on elongation in garden pea (Pisum sativum L.) plants were investigated. The auxin transport inhibitors 2,3,5-triiodobenzoic acid (TIBA) and 9-hydroxyfluorene-9-carboxylic acid (HFCA) were applied to elongating internodes of wild-type and mutant lkb plants. The lkb mutant was included because elongating lkb internodes contained 2- to 3-fold less free IAA than those of the wild type. In the wild type, TIBA reduced both the IAA level and internode elongation below the site of application. Both TIBA and HFCA strongly promoted the elongation of lkb internodes and also raised IAA levels above the application site. The synthetic auxin 2,4-dichlorophenoxyacetic acid (2,4-D) also markedly increased internode elongation in lkb plants and virtually restored petioles and tendrils to their wild-type length. In contrast, treatment of wild-type plants with TIBA, HFCA, or 2,4-D caused little or no increase in elongation above the application site. The ethylene synthesis inhibitor aminoethoxyvinylglycine also increased stem elongation in lkb plants, and combined application of HFCA and aminoethoxy-vinylglycine restored lkb internodes to the wild-type length. It is concluded that the level of IAA in wild-type internodes is necessary for normal elongation, and that the reduced stature of lkb plants is at least partially attributable to a reduction in free IAA level in this mutant.     

The role of ethylene in the growth response of submerged deep water rice

We investigated the effect of partial submergence on internode elongation in a Bangladesh variety of floating or deep water rice (Oryza sativa L., cv. Habiganj Aman II). In plants which were at least 21 days old, 7 days of submergence led to a 3- to 5-fold increase in internodal length. During submergence, the ethylene concentration in the internodes increased from about 0.02 to 1 microliters per liter. Treatment of nonsubmerged plants with ethylene also stimulated internode elongation. When ethylene synthesis in partially submerged plants was blocked with aminooxyacetic acid and aminoethoxyvinylglycine, internode elongation was inhibited. This growth inhibition was reversed when ethylene biosynthesis was restored with 1-aminocyclopropane-1-carboxylic acid (ACC). Radio-labeling studies showed that ethylene in floating rice was synthesized from methionine via ACC. Internodal tissue from submerged plants had a much higher capacity to form ethylene than did internodal tissue from nonsubmerged plants. This increase in ethylene synthesis appeared to be due to enhanced ACC formation rather than to increased conversion of ACC to ethylene. Our results indicate that ethylene produced during submergence is required for the stimulation of growth in submerged floating rice plants.     

Elongation of Stem Internodes in the Japanese Morning Glory (Pharbitis nil) in Relation to Auxin Destruction

The relationship between auxin destruction and stem internode elongation was investigated in the vines of the Japanese morning glory (Pharbitis nil Choisy). In young plants an age-dependent gradient was demonstrated in which the decreasing rate of elongation of older internodes correlated with an increasing ability of such tissue to destroy indoleacetic acid. Fragments of tissue from old internodes when incubated with indoleacetic acid (IAA), destroyed the hormone immediately and rapidly; in contrast, young, rapidly elongating internode tissue destroyed IAA only after a lag of several hours. In older plants the gradient was more erratic towards the middle of the plant but old and young tissue behaved as in young plants, i.e., old internodes destroyed IAA rapidly whereas young internodes did not. It appears reasonable to conclude that cessation of elongation in maturing internodes is brought about by developing an internal environment in which auxin is rapidly destroyed.     

Relationship of boron to gibberellic Acid-induced proliferation in debudded tobacco plants

Stem applications of gibberellic acid (GA) to debudded tobacco plants (Nicotiona tabacum L., var. One Sucker) produce stem swellings that involve intense proliferation of, primarily, xylem tissue. Withholding boron from GA-treated debudded plants greatly reduces the GA-induced proliferation. This response offers a system for directly demonstrating the effect of boron on xylem formation and lignification that is unconfounded by the effect of boron on elongation growth.     

Involvement of indole-3-acetic acid in the circadian growth of the first internode of Arabidopsis

The extension rate of the first inflorescence node of Arabidopsis was measured during light/dark or continuous light exposure and was found to exhibit oscillations which showed a circadian rhythmicity. Decapitation induced a strong inhibition of stem extension. Subsequent application of IAA restored growth and the associated extension–rate oscillations. In addition, IAA treatments, after decapitation, re-established the circadian rhythmicity visible in the intact plants during free run. This indicates that the upper zone of the inflorescence has a major influence on the extension rate of floral stems and implies a role for auxin. Application of N-(1-naphthyl)phthalamic acid, an IAA transport inhibitor, to an intact floral stem inhibited growth and the rhythmicity in the extension rate oscillations, indicating that IAA polar transport may play a role in the dynamics of stem elongation. Furthermore, IAA-aspartate application, after decapitation, did not restore growth and rhythmicity. Nevertheless, biochemical analysis of IAA and IAA-aspartate demonstrated circadian fluctuations of the endogenous levels of both compounds. These observations suggest that IAA metabolism is an essential factor in the regulation of the circadian growth rhythm of Arabidopsis floral stems. Received: 21 September 1998 / Accepted: 23 January 1999