Cytokinin-Inhibitor Antagonism in the Hormonal Control of α-Amylase Synthesis and Growth in Barley Seed

The effect of cytokinins and gibberellic acid on the inhibition of growth and α-amylase synthesis by germination inhibitors was investigated in intact and embryoless seed halves. The cytokinins, kinetin and benzyladenine, effectively reversed the inhibition of coleoptile growth and α-amylase synthesis by abscisic acid and courmarin in barley seed. An antagonism between cytokinins, kinetin and benzyladenine, effectively reversed the inhibition of coleoptile growth and α-amylase synthesis by abscisic acid and coumarins in barley seed. An antagonism between cytokinins and germination inhibitors was also shown in root growth. Abscisic acid inhibited coleoptile growth to a greater extent than the root growth while the opposite held true in the case of coumarin. The apparent increase in coleoptile growth and α-amylase synthesis by gibberellic acid plus abscisic acid (or coumarins) over abscisic acid (or coumarin) appears to be a result of the overall stimulation of growth and metabolism by exogenous gibberellic acid and probably does not involve an interaction of gibberellic acid with the inhibitors. Gibberellic acid reversed root inhibition to some extent. Abscisic acid inhibition of gibberellic acid induced α-amylase synthesis in the embryoless endosperm was not reversed by excess gibberellic acid or kinetin Cytokinin reversal of inhibition of growth and enzyme synthesis probably depends on some factor(s) in the embryo. Cytokinin reversal of inhibitor action leading to enzymen synthesis and growth may be at the level of genome or at the site protein assembly.     

Induced parthenocarpy-a way of manipulating levels of endogenous hormones in tomato fruits (Lycopersicon esculentum Mill.) 2. Diffusible hormones

Indol-3-acetic acid (IAA), gibberellin-like substances (GAs), and abscisic acid (ABA) were measured throughout the first 35 days of fruit development in agar diffusates from seeded and parthenocarpic tomato fruits. Parthenocarpic fruit growth was induced with either an auxin (4-CPA), morphactin (CME) or gibberellic acid (GA₃). IAA and GAs were at their highest levels in diffusates during the early stages of fruit growth, whereas diffusible ABA increased later. Most IAA was found in diffusates from auxin-induced and seeded fruits, whereas GAs were at their lowest levels in seeded fruits. There were only minor differences in ABA concentrations regardlesss of the treatments.Levels of diffusible hormones of tomato fruits may be easily manipulated by inducing parthenocarpic fruit growth. In spite of no obvious relationship between fruit growth and hormone levels in this study, induced parthenocarpy is considered a useful tool to further elucidate the role of hormones in fruit development and sink-source interactions.     

Effect of morphactin on stem growth in relation to auxin in precooled rooted tulip bulbs

Effect of morphactin IT 3456, an auxin transport inhibitor, on tulip stem elongation induced by indole-3-acetic acid (IAA) was investigated. Tulip stem growth induced by IAA 0.1 % in lanolin paste applied on the top internode after excision of flower bud and removal of all leaves was greatly inhibited by 0.2 % morphactin IT 3456 applied on the 4th, 3rd, 2nd and 1st internode. The inhibitory effect of the morphactin on tulips stem growth promoted by IAA was restored by additional application of IAA below the morphactin treatment place. Morphactin inhibited also the growth of all internodes induced by flower bud in the absence of leaves. These results suggest a crucial role of auxin in the control growth of all internodes in tulip stem.     

Effect of red light and gibberellic acid on lipid metabolism in germinating spores of the fern Anemia phyllitidis

The spores of the fern Anemia phyllitidis contain abundant quantities of lipid as reserve material. Germination of these spores can be induced either by red light or, even in the dark, by gibberellic acid. The effects of both these factors on lipid degradation, lipase and isocitrate lyase activities, and on the fatty acid composition have been studied in the course of the germination process. During germination in darkness with gibberellic acid, the fatty acid composition remained similar to that in the ungerminated spore. In contrast, when spores were germinated in red light, α-linolenic acid was synthesized. Little activity of lipase and isocitrate lyase could be detected in the dry spore. Red light or gibberellic acid affected a dramatic increase of the activities of these enzymes. Lipid breakdown and lipase activity were more active in red light, however. Permanent stimuli were necessary for growth and complete lipid degradation. Induction of germination simultaneously with both factors revealed an additivity of the effects of red light and gibberellic acid.     

Morphactin-kinetin interaction in lettuce seed germination and seedling growth

Summary Butylester of morphactin (n-butyl-9-hydroxy-fluorence-(9)-carboxylate) greatly inhibited seed germination and seedling growth of two strains of lettuce, Attraktion and Hohlblättriger Butter. The inhibitory effect of morphactin on seed germination was completely overcome by kinetin but the latter chemical was ineffective in reversing the morphactin induced inhibition of seedling growth. Thus it appears probable that the two substances effect seedling growth independently.     

The role of darkness, GA and fusicoccin (FC) in breaking photodormancy in Phacelia tanacetifolia seeds

The germination of the negatively photoblastic seeds of Phacelia tanacetifolia Benth. (cv. Bleu Clair) is promoted by gibberellic acid and fusicoccin. In the dark, or in the light in the presence of fusicoccin, seed germination is accompanied by an increase of gibberellic acid-like substances. In these conditions, the inhibition of the synthesis of gibberellic acid-like substances does not prevent seed germination, but it affects the growth and the survival of the seedlings. Seed germination, growth, and survival of seedlings are discussed in relation to phytochrome, fusicoccin, and gibberellic acid-iite substances.     

Effects of Germination-promoting Substances Given in Conjunction with Red Light on the Phytochrome-mediated Germination of Dormant Lettuce Seeds (Lactuca sativa L.)

Ethylene or thiourea can substitute for gibberellic acid but not for red light in breaking the secondary dormancy induced by extended dark storage of fully hydrated lettuce seeds (Lactuca sativa cv. Grand Rapids). After 10 days of storage, ethylene, thiourea, or gibberellic acid applied either separately or in any combination in conjunction with red light induced near maximal germination. When applied separately without red light, none of the substances promoted germination of seeds stored 10 days. Combinations of any two or all three of the substances in the absence of red light induced some germination but no combination was as effective as any single substance given with red light.     

The effect of some growth regulators on light-induced germination of Paulownia tomentosa seeds

Grubišié, D., Konjevié, R. and Neškovié, M. 1988. The effect of some growth regulators on light-induced germination of Paulownia tomentosa seeds. - Physiol. Plant. 72: 525–528.
The germination of Paulownia tomentosa Steud. (Empress tree) seeds can be induced either by red light (R) or by exogenously applied gibberellic acid (GA₃). The R induced germination is completely suppressed by far red irradiation, abscisic acid (ABA) or by growth retardants such as ancymidol, tetcyclacis and paclobutrazol, though not by AMO 1618 or chloro-choline chloride (CCC). The inhibition caused by far red light (FR) and growth retardants can be overcome by GA₃, while the ABA-induced inhibition can be reversed by fusicoccin (FC), which does not reverse the inhibition caused by FR or growth retardants. It is noteworthy that the germination of light insensitive wheat, corn, alfalfa and mung bean seeds is not inhibited by growth retardants.     

Developmental Differences Between Germinating After-ripened and Dormant Excised Avena fatua L. Embryos

Based on physiological and molecular differences associatedwith the germination of after-ripened and dormant caryopsesand excised embryos, it has been hypothesized that various methodsof after-ripening are the only treatments that facilitate thetransition of dormant wild oat embryos to a non-dormant state.To further investigate this hypothesis, analytical methods wereused to evaluate physical and temporal changes associated withgermination and subsequent growth of after-ripened and dormantexcised embryos (AR-embryos and D-embryos, respectively) inducedto germinate with fructose (Fru) and/or gibberellic acid (GA).While chemical treatments of Fru, GA, and Fru+GA have littleeffect on the germination and short-term growth of AR-embryos,they do induce germination of D-embryos. Growth following germinationof D-embryos varied according to treatment with the combinationof Fru+GA inducing the greatest growth over the duration ofthe experiment. Even considering differences in the time tocomplete germination, growth of D-embryos was not comparablewith that of AR-embryos. This provides physical evidence thatchemical treatments induce germination without fulfilling therequirements for normal after-ripening-enhanced germination/growth,and indicates that fructose and/or gibberellic acid do not removethe dormancy-block or rate limiting step in the same manneras after-ripening. Avena fatua ; after-ripening; dormancy; fructose; germination; gibberellic acid; wild oats     

Effects of SO2 on Photosynthesis and Nitrogen Fixation

Spikelets of Themeda triandra are dormant when mature and require an after-ripening period in dry storage of approximately 12 months before full germination potential is realized. Successful germination of spikelets entails the splitting of the tough upper glumes by radicles. Dormany appears to result from a combination of embryo dormancy and mechanically resistant glumes. Glume removal from dormant spikelets increases germination while glume removal plus gibberellic acid increases germination even more. During the after-ripening period, the growth potential of spikelets and caryopses increases as measured by their ability to germinate in the presence of the osmoticum polyethylene glycol 6000. The inhibition of germination by decreasing osmotic potential of the germination medium significantly interacts with the promotion caused by gibberellic acid indicating that both factors affect germination by altering the growth potential of the embryos. The increase in growth potential during after-ripening is probably related to the synthesis of gibberellin-like substances. It is hypothesized that dormancy breaking during after-ripening occurs because the growth potential of embryos increases and this consequently increases the ability of radicles to split the upper glumes during germination.     

Actions of gibberellic Acid and phytochrome on the germination of grand rapids lettuce seeds

Red light and gibberellic acid were about equally effective in promoting germination of Grand Rapids lettuce (Lactuca sativa L.) seeds. With initial far red light treatment more than 80% remained dormant in subsequent dark storage. After 2 days of dark storage, red light effectively promoted germination, while gibberellic acid action was weak. With between 2 and 10 days of dark storage, gibberellic acid had little effect, while promotion by red light decreased slowly and finally disappeared. After 10 days of dark storage, both gibberellic acid and red light were required for germination. The dark storage treatment interferes with phytochrome-independent germination processes and cannot be overcome by added gibberellic acid. However, storage may also decrease the effectiveness of endogenous gibberellins. Phytochrome-dependent germination seems to require only low levels of endogenous gibberellin activity or the addition of gibberellic acid. Gibberellins and red light appear to act on germination by regulation of sequential sites of a branched-looped pathway.     

Dormancy and Impotency of Cocklebur Seeds: IV. Effects of Gibberellic Acid, Benzyladenine, Thiourea, and Potassium Nitrate on the Growth of Embryonic Axis and Cotyledon Segments

Germination of nondormant but impotent small cocklebur seeds (Xanthium pennsylvanicum Wallr.) was promoted profoundly with thiourea or benzyladenine, and slightly with gibberellic acid. Gibberellic acid was ineffective in causing the germination of dormant cocklebur seeds, although thiourea and benzyladenine were effective. Experiments with excised seed pieces showed that the promotive effects of thiourea, benzyladenine, and gibberellic acid on cocklebur seed germination were associated with the enhancement of growth of seed parts; thiourea stimulated predominantly the axial growth, whereas benzyladenine stimulated predominantly the cotyledonary growth.     

Germination characteristics of some plant species from calcareous fens in southern Germany and their implications for the seed bank

Seeds of 25 plant species from calcareous fen hay meadows were exposed to different experimental conditions and their germination was characterised. Constant temperature inhibited germination especially in Cyperaceae . Both gibberellic acid and potassium nitrate failed to terminate dormancy. Increased germination rates were found in dicot species after treatment with gibberellic acid. Temperature fluctuations increased germination of Cyperaceae as well as dicotyledons. Treatment with gibberellic acid removed the chilling requirement in some of the species. Dormancy of small seeds with thin seed coats was broken by the application of gibberellic acid or fluctuating temperature; large thick-coated seeds were unaffected by gibberellic acid. No obligatory darkness requirement was found in any species; three species germinated irrespective of light treatments. All other species achieved higher percentage germination in daylight or in red (670 nm) light. Permanent darkness and far-red light (730 nm) reduced germination drastically. The results indicate that germination characteristics of the species investigated can be related to their seed bank types.     

Dependence of gibberellic acid-induced dark germination of lettuce seed on RNA synthesis

Summary Gibberellicacid-induced dark germination of Grand Rapids lettude seed was completely inhibited by 6-azauracil and partly by 2-thiouracil. Other inhibitors of nucleic acid and protein synthesis used were without effect. Inhibition of gibberellic acid-induced dark germination was reversed by uracil but not by thymine, deoxycytidine and orotic acid. The results suggest that gibberellic acid-induced dark germination is dependent on RNA synthesis and not on DNA synthesis.Gibberellic acid-induced lettuce hypocotyl growth was inhibited by all the inhibiters of nucleic acid and protein synthesis used, including actinomycin D, puromycin, chloramphenicol and p-fluorophenylalanine.Approved by the Director of the New York State Agricultural Experiment Station for publication as Journal Paper No. 1507.     

Induced parthenocarpy—a way of changing the levels of endogenous hormones in tomato fruits (Lycopersicon esculentum Mill.) 1. Extractable hormones

Ethylene, indol-3-acetic acid (IAA), gibberellin-like substances (GAs) and abscisic acid (ABA) were analysed in extracts from normal, seed-containing and parthenocarpic tomato fruits throughout fruit development. Parthenocarpic fruit growth was induced with an auxin (4-CPA), morphactin (CME) or gibberellic acid (GA₃) and compared with that of pollinated control fruits. Fruit growth was only affected by the treatment with GA₃, decreasing size and fresh weight by 60%. The peak sequence of hormones during fruit development was ethylene-GAs-IAA-ABA. Seeded fruits contained the highest levels of IAA and ABA but the lowest levels of GAs. Also, in seeded fruits, a high proportion of IAA and ABA was found in the seeds whereas this was not the case for GAs.Hormone levels of tomato fruits may be successfully, easily and reproducibly altered by inducing parthenocarpic fruit growth and thus eliminating development of seeds which are a major source of hormone synthesis. In spite of markedly changed hormone levels, there was no obvious relationship between fruit growth and extractable hormones per se. However, the results indicate that a high ratio of GAs: auxins is unfavourable for growth of tomato fruits.     

The physiological basis of seed dormancy in Avena fatua L. I. Action of the respiratory inhibitors sodium azide and salicylhydroxamic acid

The dormancy breaking effect of sodium azide was studied in seeds of several genetically pure lines of Avena fatua L. isolated from field populations. Sodium azide (0.8 and 1 m M ) induced germination in several dormant lines (characterized by long term dormancy) after two weeks of treatment. By about five weeks, germination was nearly complete in azide treated seeds as compared to little or no germination in controls. (2-chloroethyl) trimethylammonium chloride (an inhibitor of gibberellin biosynthesis) completely inhibited the azide effect suggesting that stimulation of germination by azide requires gibberellin biosynthesis. Azide was very effective in breaking dormancy in lines AN-51, AN-86, AN-127 and AN-265, but failed to induce germination in Montana 73. In this line there was a synergism between azide and gibberellic acid in promotion of germination. Thus, at least two metabolic blocks are involved in the stimulation of germination in this line. Salicylhydroxamic acid (an inhibitor of alternative respiration) at 3 m M completely inhibited the germination induced by 1 m M azide. At this concentration, salicylhydroxamic acid did not inhibit germination in 1) genetically nondormant seeds (line SH-430), 2) afterripened seeds of a dormant line (AN-51), and 3) gibberellic acid-treated dormant seeds. These findings suggest that salicylhydroxamic acid-sensitive process(es), presumably alternative respiration, is necessary for the stimulation of germination in the presence of azide, but not in the germination of genetically nondormant, gibberellic acid-treated dormant, or afterripened seeds.     

Metabolically active glucosides in oleaceae seeds: I. The effects of germination, growth, and hormone treatments

The seeds of six woody species of Oleaceae representing three genera, contain high concentrations of water-soluble glucosides, with major absorption maxima below 240 nanometers. In Fraxinus americana seeds three of these compounds, designated GL-3, GL-5, and GL-6, account for almost 10% of the dry weight. They are found in the endosperm and embryo but not in the pericarp. While the level of GL-5 is not particularly influenced by the physiological state of the embryo, that of GL-3 and GL-6 decreases as a result of germination and growth during a 10-day period. As the concentrations of GL-3 and GL-6 decrease, new ultraviolet-absorbing compounds are formed. The changes in the concentration of the ultraviolet-absorbing glucosides during cold temperature after-ripening, prior to germination, are small. When germination of dormant embryos is induced with gibberellic acid, the concentrations of GL-3 and GL-6 decrease in a manner similar to that observed with nondormant embryos. In the presence of abscisic acid no losses of GL-3 and GL-6 were observed. It is suggested that GL-3 and GL-6 fulfill some definite functions in the germination and growth of F. americana embryos, and that gibberellic acid and abscisic acid can exert a regulatory effect on the metabolism of these glucosides.     

Plant growth regulators and adventitious root development in relation to auxin

Adventitious root formation in stem cuttings of mung bean was enhanced by ethrel, which had an additive effect when employed simultaneously with indolebutyric acid (IBA). Abscisic acid (ABA) did not influence the number of roots per cutting whereas gibberellic acid (GA₃) and kinetin were without effect on rooting at lower concentrations but were inhibitory at higher concentrations. Nevertheless, all three of these chemicals showed synergistic interactions with IBA and/or indol-3-ylacetic acid (IAA) and thereby significantly promoted root formation. A localised application of morphactin to the epicotyl of cuttings totally inhibited root production irrespective of which of the foregoing growth regulators were suppliedvia the hypocotyl. Morphactin application also prevented root formation in cuttings treated with vitamin D₂. The various growth regulators employed had differing effects on growth of roots but there was no simple relationship between their effects on root formation and subsequent root growth.     

Effects of Dormancy Regulating Chemicals on Innate and Salinity Induced Dormancy in the Invasive <Emphasis Type="Italic">Prosopis juliflora</Emphasis> (Sw.) DC. Shrub

The effect of different types and concentrations of dormancy regulating chemicals (DRCs) on innate and induced dormancy was evaluated under optimal germination conditions in the invasive Prosopis juliflora shrub. Lower concentrations of gibberellic acid (0.3 mM) and kinetin (0.05 mM) were more effective in enhancing germination % and rate at higher concentrations of NaCl, but the reverse was true for thiourea. None of the DRCs alleviated innate dormancy of P. juliflora. Germination % and rate decreased as salinity increased. Percent final germination of non-treated seeds was significantly reduced at 500 mM NaCl and virtually inhibited in 600 mM NaCl. Germination reduction in 500 mM NaCl was not alleviated by any of the DRCs, but inhibition induced at 600 mM NaCl was partially alleviated by all the DRCs. Gibberellic acid had a significantly greater effect than kinetin in alleviating germination inhibition. For restoration of saline soil through the use of P. juliflora, results suggest using DRCs, particularly gibberellic acid and thiourea, as a preseeding treatment can overcome the problem of reduced germination.     

Inhibitors from Carob (Ceratonia siliqua L.) I. Nature of the Interaction With Gibberellic Acid on Shoot Growth

Concentrated whole extracts of the immature fruit of carob and 3 fractions derived from this extract have been shown to inhibit the gibberellic acid induced growth of pea seedlings. The inhibition can be completely reversed by increasing the amount of gibberellic acid. The inhibitors do not reduce the endogenous growth of seedlings but only that induced by gibberellic acid. One of the fractions is a newly separated one not previously reported.