The control of flower initiation by gibberellin in Helianthus annuus L. (sunflower), a non-photoperiodic plant

The involvement of gibberellins in the control of flowering of sunflower was studied by direct application of GA₃ to the apex of the plants, analysis of the endogenous levels of gibberellin-like substances at different plant ages, and indirectly by the application of paclobutrazol, an inhibitor of gibberellin synthesis. GA₃ speeded-up flower initiation and floral apex development. The time of GA₃ application was more critical than the amount of GA₃ applied. The endogenous levels of gibberellin-like compounds increased significantly by day 15 after sowing. The application of paclobutrazol markedly delayed floral initiation and this effect was also depedent on plant age. Both GA₃ and paclobutrazol had their greatest effects between 10 and 20 days after sowing suggesting that an increase in gibberellins in that time period plays a role in floral initiation.     

Periodicity of bud bursting in willow (Salix viminalis) as affected by growth regulators

Saunders, P. F. and Barros, R. S. 1987. Periodicity of bud bursting in willow ( Salix viminalis ) as affected by growth regulators.
Lateral vegetative buds of willow ( Salix viminalis L.) were only innately dormant for 3–5 weeks in October; during this time their apices were correlatively inhibited by the bud leaflets. Exogenous gibberellins stimulated the opening of cultured buds when the plants were dormant or entering dormancy. As dormancy was being released, however, cultured buds became more responsive to exogenous cytokinins. Thus the demand for gibberellins and cytokinins for bud opening seemed to be sequential rather than simultaneous. Dormant buds cultured in the presence of abscisic acid remained unopened, but they opened after a chilling treatment. Subsequent growth of such buds as measured by dry matter accumulation, was observed only if a cytokinin was added to the medium.     

Gibberellin involvement in dormancy-break and germination of seeds of celery (Apium graveolens L.)

The temperature-dependent, primary dormancy of cv. Florida 683 celery seeds in darkness was partially broken by a 30 min light exposure on the third day of incubation at 20–22°C, resulting in c 50 percent germination after 20 days. This light stimulation was negated by including different inhibitors of gibberellin biosynthesis in the incubation medium. Subsequent addition of a solution of the gibberellins A₄ and A₇ or of the gibberellin-active compound (1-3-chlorophthalimido)-cyclohexane carboxamide (AC94,377) overcame the inhibitory effects on germination of these GA-biosynthesis inhibitors. It is suggested that light stimulates the biosynthesis of gibberellins which are essential for dormancy-break in celery seeds and that this biosynthesis is either directly or indirectly controlled through phytochrome.Abbreviations AC94,377 1-(3-chlorophthalimido)-cyclohexane carboxamide; ancymidol, -cyclopropyl--(4-methoxyphenyl)-5-pyrimidinemethanol - AMO1618 N,N,N-2-tetramethyl-5-(1-methyl ethyl)-4-(1-piperidinylcarbonyl)oxy-benzenaminium chloride - BTS44584 S-2,5-dimethyl-4-pentamethylenecarbamoyloxyphenyl-SS-dimethyl sulphonium - P toluenesulphonate; chlormequat chloride, 2-chloroethyltrimethylammonium chloride; daminozide - N dimethylaminoscuccinamic acid; paclobutrazol, (2RS, 3RS)-1-(4-chlorophenyl)-4,4-dimethyl-2-(1H-1,2,4-triazol-1-yl pentan-3-ol)     

Auxins,ABA and gibberellin-like activity in abscising and non-abscising flowers and pods of Vicia faba L.

Abscission probability varies among floral positions within inflorescences of Vicia faba L. Flowers from proximal positions have a greater chance to develop into mature pods than flowers from more distal positions which normally abscise either as older flowers or as young pods. In three field experiments with the indeterminate single stem variety Herz-Freya, changes in the contents of extractable auxins, abscisic acid (ABA) and gibberellins in flowers and pods during their development, and their possible influence on abscission were investigated.Inflorescences at different positions along the stem were divided into the two proximal and the remaining fruits. The content of all three hormones was at a low level during flower development, increased greatly in parallel with dry matter accumulation in the young pods, and then decreased to maturity. The first hormone to increase in the fruits was auxin and this took place when abscission from the distal positions began. ABA and gibberellins at this time were still at a low level. This ontogenic course of hormone production was very similar in fruits of both positions within an inflorescence, but in flowers and young pods from proximal positions, auxin content in most inflorescences was greater than in those from the abscising distal positions. No such positional differences were observed with ABA and gibberellins. Decapitation of the plants reduced flower and pod drop from the remaining reproductive nodes. Although decapitation resulted in less abscission among distal flowers and young pods from these nodes, it did not affect the ontogenic course of auxin and ABA production in these fruits.     

Development of fertilized ovules and their role in the growth of the pea pod

The histological development of fertilized ovules during fruit-set and development in pea ( Pisum sativum L. cv. Alaska) has been investigated. Killing the ovules on day 0 (anthesis) or day 1 prevented fruit-set and resulted in ovary degeneration. When the ovules were destroyed at later stages the ovaries developed, though the rate of growth of the pod was reduced significantly. Pollination in pea occurs normally the day before anthesis, and fertilization of the egg cell 32 to 48 h later. The first divisions of the zygote and endosperm nuclei started simultaneously (ca 48 h after pollination) but the endosperm developed more rapidly than the embryo; the embryo sac cavity was lined with free endosperm nuclei at the time of beginning suspensor elongation. Extracts of endosperm and ovule coats from ovules at day 7 after anthesis showed fruit-set activity in pea, the latter material having about 3 times more activity than the former per ovule basis. These results indicate that fertilization of the ovule is necessary for fruit-set in pea, and that compounds which induce fruit-set are probably synthesized in the ovules following fertilization.     

Hormonal changes associated with leaf senescence in cotton (Gossypium barbadense)

To study the hormonal regulation of foliar senescence in cotton ( Gossypium barbadense L. cv. Giza 68, long staple), the sequential changes in gibberellins (GAs), indoleacetic acid (IAA) and abscisic acid (ABA) were examined in the cotyledons from the completion of expansion through senescence (days 12-24 after sowing). The onset of senescence could be detected on day 20, the stage of maximum accumulation of leaf metabolites. At this stage, free GAs quickly lost more than 40% of their initial activity. Further decrease of free GAs was then characteristically observed in the senescent leaves. A remarkable increase in free IAA and free ABA between days 18 and 20 immediately followed by nutrient depletion, suggests the contribution by both hormones to the senescence system. The definite drop in free IAA below its initial level occurred on day 24, when most of the leaf protein and chlorophyll were already broken down.     

The effect of drought on levels of abscisic acid,cytokinins, gibberellins and ethylene in aeroponically-grown sunflower plants

Abscisic acid (ABA), cytokinins and gibberellin-like substances (GAs) were extracted from the roots and shoots of 17-day-old sunflower seedlings which had been droughted or were unstressed. Plants were grown in an aeroponic chamber which allowed for good control over degree of water stress and easy access to roots. Following methanolic extraction of lyophilized material, cytokinins were separated from the acidic growth-regulators on a cellulose PO₄ cationic exchange column. The cytokinins were analysed by paper chromatography and HPLC and the soybean hypocotyl section assay. Semipurified acidic regulators were chromatographed on SiO₂ columns and HPLC and aliquots assayed with the dwarf rice cv. Tan-ginbozu bioassay for GAs. Fractions known to contain ABA were purified by sequential reverse-phase HPLC of the acid and then of the methyl ester forms followed by quantitation as Me-ABA on GLC-EC. ABA losses were measured by using an internal standard [³H]-ABA). Ethylene production was also monitored in stressed and unstressed seedlings.The effect of drought on GAs and ethylene was minimal. The ABA levels were markedly higher in droughted plants. Stressed roots had 32 times more ABA than controls. The levels of cytokinins in the shoots of droughted plants were about half those in unstressed shoots, and qualitative differences occurred in the roots. Under stress a large peak of activity was present similar to zeatin glucoside which was not present in the unstressed condition. The results are discussed in relation to drought-effects on metabolism.     

The possible involvement of gibberellins and calcium in tipburn of Chinese cabbage: Study of intact plants and detached leaves

Spraying Chinese cabbage seedlings [Brassica pekinensis (Lour.) Rupr.] with the growth retardant daminozide (succinic acid-2,2-dimethylhydrazide) reduced tipburn of the mature plants. As the concentration of daminozide increased, the reduction in tipburn damage was correlated with increased calcium content in young susceptible leaves. This effect was much more pronounced in plants that were misted once a day during the head formation period.Incubation of detached Chinese cabbage leaves for 48 h (in the dark) in solutions which contained either EDTA or EGTA caused characteristic lesions at the leaf tips. The extent of the damage was reduced by including CaCl₂ in the solutions. Leaves which were incubated in a solution of EDTA+GA₃ or EGTA+GA₃ were severely affected, with the latter solution being the more harmful. GA₃ alone did not enhance tipburn. CaCl₂ greatly reduced the effect of a complex of chelating agents and GA₃. Leaves derived from daminozide-treated plants which were incubated in EDTA+GA₃ were less affected with tipburn lesions than leaves of control plants treated with the same solutions. When detached leaves were water-stressed for 24 h prior to incubation in these solutions, the severity of tipburn symptoms increased. The possible interactions between GA, calcium chelation and tipburn development are discussed.Contribution no. 1171-E, 1984 series, from the ARO, The Volcani Center Bet Dagan, Israel.     

Metabolism of gibberellins in a cell-free system from immature seeds of Phaseolus vulgaris L.

The biosynthetic steps from gibberellin A₁₂-aldehyde (GA₁₂-aldehyde) to C₁₉-GAs were studied by means of a cell-free system from the embryos of immature Phaseolus vulgaris seeds. Stable-isotope-labeled GAs were used as substrates and the products were identified by gas chromatography-mass spectrometry. Gibberellin A₁₂-aldehyde was converted to GA₄ via non-hydroxylated intermediates and to GA₁ via 13-hydroxylated intermediates. 13-Hydroxylation took place at the beginning of the pathway by the conversion of GA₁₂-aldehyde to GA₅₃-aldehyde. The conversion of GA₂₀ to GA₅ and GA₆ was also shown but no 2-hydroxylating activity was found. Endogenous GAs from embryos and testas of 17-dold seeds were re-examined by gas chromatography-selected ion monitoring using stable-isotopelabeled GAs as internal standards. Gibberellins A₉, A₁₂, A₁₅, A₁₉, A₂₃, A₂₄, and A₅₃ were identified for the first time in P. vulgaris, in addition to GA₁, GA₄, GA₅, GA₆, GA₈, GA₁₇, GA₂₀, GA₂₉, GA₃₇, GA₃₈ and GA₄₄, which were previously known to occur in this species. The levels of all GAs, except the 2-hydroxylated ones, were greater in the embryos than in the testas. Conversely, the contents of GA₈ and GA₂₉, both 2-hydroxylated, were much higher in the testas than in the embryos.Abbreviations GA_n gibberellin A_n - GC-MS gas chromatography-mass spectrometry - GC-SIM gas chromatography-selected ion monitoring - HPLC high-performance liquid chromatography - TLC thin-layer chromatography - m/z ion of mass     

Metabolism of [3H]gibberellin A4 in somatic suspension cell cultures of carrot

The native gibberellin A₄ (GA₄), in radioactive form ([1,2-³H]GA₄, 1.06 Ci/mmol), was fed to carrot somatic cell cultures (suspension and immobilized cell systems) and its metabolism over a 48 hr period was investigated. It was found that the [³H]GA₄ was metabolized to at least two GAs, [³H]GA₁ and [³H]GA₈, six GA glucosyl conjugates, [³H]GA₁-0(3)-glucoside, [³H]GA₁-0(13)-glucoside, [³H]GA₁-glucosyl ester, [³H]GA₄-glucoside, [³H]GA₄-glucosyl ester, a [³H]GA₈ glucosyl conjugate(s) and a previously unknown [³H]GA₁ glucosyl conjugate ([³H]GA₁-0(3,13)-diglucoside-like compound). The GA₁-diglucoside-like compound was found only in extracts of cells and was present in significant amounts (33 % of total extractable radioactivity). All other metabolites were present in both cells and medium. For extracts of the medium, no differences between the suspension and immobilized cultures existed in types of [³H]GA₄ metabolites although quantitative differences were apparent.