Gibberellic acid and the inhibition of aerial tuberisation in Solanum tuberosum L.

The sensitivity of aerial and subterranean tuberisation to photoperiod was studied in potato (Solanum tuberosum cv. Aracy). Although photoperiodic sensitivity varied with the position along the stem, all buds could be induced to develop tubers under SD. Gibberellic acid (GA₃) applied to induced (30 short days) cuttings inhibited the photoperiodic effect. No tubers were formed and orthotropic shoots developed instead. The GA₃ caused a reduction in starch content in induced buds, lowering it to the same level as found in long-day treated plants. However, -amylase activity of buds of induced plants was not affected by GA₃, suggesting that GA₃ does not inhibit tuberisation by promotion of starch hydrolysis.     

Stem elongation and floral initiation on in vitro chicory root explants: influence of photoperiod

Chicory root explants (Cichorium intybus L.) were cultured in vitro under different photoperiods. In complete darkness, strong stem elongation, but no flowering induction was observed. We suggest that this stem elongation could be homologous to the pit growth in chicory heads in vivo. Under a photoperiod of 12 h (LI=±40 E m^–2 s^–1), only vegetative growth was observed. Photoperiods of 16 h or more light a day induced the in vitro explants to develop stems bearing flower buds. When the in vitro cultures were kept in the dark for different durations starting from the first day of culture and afterwards transferred to long-day conditions, 4 days dark were sufficient to cause a decrease in flowering induction. We suggest that during the dark culture, a flowering inhibitory process was started.     

Inhibition of stem growth and gibberellin production in Agrostemma githago L. by the growth retardant tetcyclacis

The effects of the new growth retardant tetcyclacis (TCY) on stem growth and endogenous gibberellin (GA) levels were investigated in the long-day rosette plant Agrostemma githago. Application of TCY (10 ml of a 5·10^-5M solution daily) to the soil suppressed stem elongation in Agrostemma grown under long-day conditions. A total of 10 g GA₁ (1 g applied on alternate days) per plant overcame the growth retardation caused by TCY.Control plants and plants treated with TCY were analyzed for endogenous GAs after exposure to nine long days. The acidic extracts were fractionated by high-performance liquid chromatography. Part of each fraction was tested in the d-5 maize bioassay, while the remainder was analyzed by combined gas chromatography-selected ion monitoring. The bioassay results indicated that the GA content of plants treated with TCY was much lower than that of untreated plants. The data obtained by gas chromatography-selected ion monitoring confirmed that the levels of seven GAs present in Agrostemma were much reduced in TCY-treated plants when compared with the levels in control plants: GA₅₃ (13%), GA₄₄ (0%), GA₁₉ (1%), GA₁₇ (33%), GA₂₀ (15%), GA₁ (4%), and epi-GA₁ (13%). These results provide evidence that TCY inhibits stem growth in Agrostemma by blocking GA biosynthesis and thus lowering the levels of endogenous GAs.Abbreviations AMO-1618 2-isopropyl-4-dimethylamino-5-methylphenyl-1-piperidine-carboxylate methyl chloride - GA(s) gibberellin(s) - HPLC high-performance liquid chromatography - TCY Tetcyclacis (5-[4-chlorophenyl]-3,4,5,9,10-pentaaza-tetracyclo-5,4,1,0^2,6,0^8,11-dodeca-3,9-diene)     

The control of in vitro direct main stem formation of Lilium longiflorum derived from receptacle culture, and rapid propagation by using in vitro stem nodes

The control of in vitro direct main stem formation by culturing receptacles, and a protocol for the micropropagation of Lilium longiflorum using in vitro main stem nodes derived from receptacle culture were developed. Receptacles from flowers cultured on MS medium containing 1.0 mg l^–1 gibberellic acid (GA₃) and 0.5 mg l^–1 6-benzyladenine (BA) resulted in direct main stem formation after 3 months culture. These stems were isolated and cut into nodal stem segments, which were then cultured on MS medium supplemented with 0.2 mg l^–1 BA. Shoots formed on each node after one month culture. These shoots were subcultured on MS medium containing 0.5 mg l^–1 BA for their mass propagation. An average of 30 vigorous and uniform shoots were formed per single shoot after each subculture. A cyclic and continuous system of propagation by multiplication of shoots was developed. Shoots were rooted on 1/2 MS medium containing 0.2 mg l^–1-naphthaleneacetic acid (NAA). One hundred plantlets that were acclimatized in the greenhouse had a 100% survival. A comparison was made with the traditional culture of explants derived from bulb-scales and with that from main stems.     

Further studies on the metabolism of gibberellins (GAs) A9, A20 and A29 in immature seeds of Pisum sativum cv. progress No. 9

Seed maturation of Pisum sativum cv. Progress No. 9 proceeds more slowly in winter than in summer even when the parent plants are grown in greenhouse conditions with light-and heat-supplementation. For parent plants grown under summer and winter conditions the metabolism of [³H]GA₉ in cultured seeds is qualitatively different in seeds of equivalent age and qualitatively the same in seeds of equivalent weight. 13-Hydroxylation of [³H]GA₉[³H]GA₂₀ is restricted to early stages of seed development. 2-Hydroxylation of [³H]GA₉2-OH-[³H]GA₉ has only been observed at a stage of development after endogenous GA₉ has accumulated. 2-OH-GA₉ has been shown to be endogenous to pea and is named GA₅₁. H₂-GA₃₁ and its conjugate have not been shown to be present in pea and may be induced metabolites of [³H]GA₉. The metabolism of GA₂₀GA₂₉ is used to illustrate a technique of feeding [²H][³H]GAs in order to distinguish a metabolite from the same endogenous compound. The in vitro conversion of [³H]GA₂₀[³H]GA₂₉, and the virtual non-metabolism of [³H]GA₂₉ have been confirmed for seeds in intact fruits. These results are discussed in relation to the apparent absence of conjugated GAs in mature pea seeds.Abbreviations GA_n gibberellin A_n - GC gas chromatography - GC-MS combined gas chromatography-mass spectrometry - GC-RC combined gas chromatography-radio counting - Me methyl ester - R_T etention time - SICM selected ion current monitoring - TLC thin layer chromatography - TMS trimethyl silyl ether The author is née Frydman     

Gibberellic acid causes earlier flowering and synchronizes fruit ripening of coffee

The effect of 100 mgl^–1 gibberellic acid (GA₃) on flowering and fruit ripening synchrony, fruit set, fruit fresh weight, and vegetative growth were studied for different size classes of coffee (Coffea arabica L. cv. Guatemalan) flower buds. Flower buds that were > 4 mm, but not developed to the candle stage at the time of GA₃ treatment, reached anthesis 20 days earlier than the controls, and their development was independent of precipitation, unlike the controls. Fruit from buds that were treated with GA₃ at the candle stage showed earlier and more synchronous ripening than the control, although no differences in flowering were found during anthesis. Buds that were smaller than 4 mm at the time of treatment did not respond to GA₃ applications. Treatment with GA₃ did not affect fruit set, fresh weight of fruits, or vegetative shoot growth.     

Comparison of de-novo flower-bud formation in a photoperiodic and a day-neutral tobacco

Regeneration of flower buds in thin tissue layers from pedicels of photoinduced short-day (SD) tobacco, Nicotiana tabacum L. cv. Maryland Mammoth, is described. Up to seven flower buds per explant were obtained in a medium containing Murashige and Skoog's macro- and microclements, 100 mg/l myoinositol, 0.1 mg/l thiamine-HCl, 6% glucose, 5 M N⁶-benzylaminopurine, and 0.5 M -naphthaleneacetic acid. Usually some vegetative buds were also formed in the pedicel thin tissue layers. Thin tissue layers from other positions in the induced SD tobacco regenerated vegetative buds only. A comparative study with a day-neutral (DN) tobacco, Samsun, showed that the capacity to form de-novo flower buds was more localized and less strongly determined in photoperiodic than in the DN tobacco. The differences between the photoperiodic and DN tobaccos in flower-bud regeneration capacity are thus quantitative and not qualitative. The basis for this quantitative difference is not known, but may depend on factors controlling production of floral stimulus (florigen) and competency of cells to respond to florigen, and-or stability of the determined state to form flower buds in vitro.Abbreviations BAP N⁶-benzylaminopurine - DN day-neutral - GA₃ gibberellic acid - LD long-day - MM Maryland Mammoth - NAA -naphthaleneacetic acid - SD short-day     

Dormancy in peach (Prunus persica L.) flower buds

Summary Peach buds (floral and vegetative) were periodically collected from midsummer until the spring flowering and sprouted under continuous light, 100% relative humidity and 20–25°C. Treatments with 200 ppm gibberellin A₃ (GA₃) or chilling (2–4°C for 30 days before planting) were applied. Vegetative buds showed well-defined phenological stages: pre-dormancy, true dormancy, and end of dormancy. Both GA₃ and chilling treatments shortened the sprouting times of vegetative dormant buds close to those in predormancy. Isolated floral buds were irresponsive under all conditions and did not sprout even with the GA₃ or chilling treatments. In a comparative study with buds immediately after collection anatomical analysis demonstrated that vegetative buds were almost completely developed by midsummer/early automn and remained in a resting state until the end of winter. Floral buds developed continuously over the same period. Both types of verticils began to differentiate in midsummer. Sepals and petals developed mainly in late summer, androecious floral parts developed throughout the resting period, while gynoecious floral parts showed differentiation in late winter. The flower was completely formed a few days prior to blossoming. Thus, in isolated peach buds fertile verticils are not sufficiently developed during the resting time to allow sprouting.     

Light and ethylene effects on assimilate distribution,acid invertase activity and keeping quality of begonia

Flowering plants of Begonia × cheimantha cv Emma and Begonia x hiemalis cv Schwabenland Red were exposed to different light levels (0, 40, 80 M m^–2S^–1) and to ethylene (150 nl 1^–1) in growth cabinets. Increasing irradiance level increased the number of flower buds in both begonia species. The amount of ¹⁴C-assimilates translocated to flower buds and the acid invertase activity in flower buds and flowers also increased with increasing irradiance level. Conversely, treatment with ethylene decreased the accumulation of ¹⁴C in flowers and flower buds, but did not affect acid invertase activity. Ethylene accelerated abscission of flowers and flower buds and increased the number of cup shaped and small flowers.     

Stimulation of in vitro shoot proliferation from nodal explants of cassava by thidiazuron, benzyladenine and gibberellic acid

Multiple shoots were produced from nodal explants of cassava (Manihot esculenta Crantz) by a two-step procedure: a 6- to 8-day exposure to 0.11–0.22 µM thidiazuron (TDZ) in liquid Murashige and Skoog (MS) medium followed by culture on agar-solidified MS medium supplemented with 2.2 µM 6-benzyladenine (BA) and 1.6 M gibberellic acid (GA₃). TDZ caused the nodal explants to expand and this expansion (growth) continued during culture with BA and GA₃. From this expanded explant, clusters of buds and fasciated stems developed continuously and these gave rise to shoots. The shoot proliferation process was open-ended, yielding an average of 31.5 shoots per nodal explant after 10 weeks of culture with genotype CG 1–56. A positive response was also obtained from seven other genotypes evaluated with this protocol.Abbreviations BA 6-benzyladenine - BM basal medium - DPU 1,3-diphenylurea - GA₃ gibberellie acid - 2iP isopentenyladenine - MSM multiple shoot medium - NAA 1-naphthaleneacetic acid - PGR plant growth regulator - TDZ thidiazuron - Z zeatin     

Effects of ascorbic acid on axillary shoot induction in Tylophora indica (Burm. f.) Merrill.

A procedure for rapid in vitro multiplication of Tylophora indica (Burm. f.) Merrill., an important indigenous medicinal plant, has been developed. Addition of ascorbic acid was essential to induce sprouting of axillary buds. Optimum multiplication was observed on MS medium containing 6-benzylamino purine (5.0 mg l^–1), -naphathalene-acetic acid (0.5 mg l^–1) and ascorbic acid (100 mg l^–1). Rooting of in vitro produced shoots was readily achieved with indole-3-acetic acid alone (1.0 mg l^–1) in MS. The plantlets thus obtained were successfully transferred to pots in large numbers which grew normally.Abbreviations BAP 6-benzylamino purine - 2,4-D 2,4-dichlorophenoxyacetic acid - GA₃ gibberellic acid - IAA indole-3-acetic acid - IBA indole-3-butyric acid - 2ip 2-isopentenyladenine - Kn kinetin - MS Murashige & Skoog media - NAA -naphthalene acetic acid     

Interactions of daminozide, 2, 2′-dipyridyl,and gibberellins A3, A9 and A20, in stem extension inChrysanthemum morifolium Ramat: an indication that daminozide may not inhibit the responses to GA9 or GA20 by blocking gibberellin hydroxylation

Interactions between the growth retardant daminozide (a substituted succinamic acid) and a subsequent application (1 or 10 g) of either gibberellin A₃, A₉ or A₂₀, on stem extension inChrysanthemum morifolium cv. Bright Golden Anne, indicated that pre-treatment of plants with daminozide largely prevented the response to GA₂₀ as well as to GA₉. The daminozide-GA₃ interaction on total stem length was dependent upon the dose of GA₃ such that, by flowering time, 1 g of GA₃ had virtually eliminated the retardant effect, while 10 g of GA₃ increased stem length to a value similar to that achieved by control shoots receiving 10 g of GA₃. In contrast, prior application of 2, 2-dipyridyl (an inhibitor of hydroxylation in some plant and animal systems) had no significant influence on the time courses of response to any of the GAs. In the absence of daminozide (and 2, 2-dipyridyl) all three GAs were very active in promoting internode extension soon after their application. If 2, 2-dipyridyl can block hydroxylation reactions in chrysanthemum tissues, the results do not support the hypothesis that daminozide restricts GA₉- (or GA₂₀-) induced stem elongation by preventing the hydroxylation of GA₉.     

In vitro vegetative propagation of Chinese cabbage

Explants from cotyledons, axillary buds, inflorescence stems and flower buds of Brassica campestris ssp. pekinensis (Lour.) Olsson (Chinese cabbage, cv. Wongbok) were cultured on MS medium with growth regulators. Multiple shoots were obtained from cotyledons, axillary buds and flower buds but not from inflorescence stems. Propagation of shoots from cotyledons was more successful than from axillary buds and flower buds. The vegetative propagation rates varied amongst clones derived from cotyledons of the same cultivar and seed lot. The propagation rates of the cotyledon-derived material followed a normal distribution with an average propagation rate of 2.6 shoots per two weeks subculture when cultured on MS media plus 44.4 m benzyladenine (BA) and 14.8 m -indolebutyric acid (IBA). Shoots from three clones were cultured on MS medium with nine different concentrations of BA. The concentration of BA which promoted the highest rate of shoot propagation varied for the three clones and was in the range 44.4 to 177.6 m.     

The control by gibberellic acid of stem elongation and flowering in biennial plants of Centaurium minus Moench

Summary Application of a small amount of gibberellic acid (GA₃) to unvernalized rosettes of a biennial strain of Centaurium minus Moench brings about immediate stem elongation under both long days (LD) and short days (SD), but the rate of stem elongation falls after the cessation of treatment. Under LD, but not SD, a second period of rapid and prolonged stem elongation may subsequently take place, associated with flowering. Extended GA₃ treatment under SD leads to the formation of a long stem but not to flowering; after the treatment the plants revert to vegetative aerial rosettes unless transferred to LD prior to the cessation of stem elongation; after such a transfer, rapid stem elongation and flowering may be initiated. If flower primordia are initiated under LD, stem elongation and formation of flower primordia continue after transfer to SD, though flowers do not develop fully. It is suggested that under LD but not SD applied GA₃ may bring about the production of endogenous gibberellin, and that this synthesis of endogenous gibberellin occurs in the flower primordia.     

The effect of light quality and gibberellic acid (GA3) on photosynthesis and respiration rates of pea seedlings

CO₂ exchange were measured on pea seedlings (Pisum sativum L. var. Bördi) cultivated from seeds imbibed either in water (C-plants) or in gibberellic acid (GA₃) at the concentration of 25 g/1 (GA-plants), and then grown under 17 W/m² blue light (B-plants) or 11 W/m² red light (R-plants).When measured under the same light conditions as during growth the net photosynthesis (APS) rate in B-plants was about twice higher than that in R-plants. Dark respiration (DR) rate was 70% higher in B- than in R-plants. Red light retarded the development of photosynthetic activity, but GA₃ suppressed this effect. The hormone enhanced net photosynthesis and dark respiration to the same extent.When measured under saturating white light net photosynthesis rate of C-plants was also two times higher in B-plants than in R-plants. Growth conditions had only a slight effect on the APS of GA-plants under white light. APS rates of GA-plants grown under red light were higher under white light than those of C-plants, but lower than those of plants grown under blue light.We assume that blue light induced formation of plants that were adapted to higher light intensity: red light had an opposite effect, whereas gibberellic acid induced formation of plants that were adapted to medium light intensity.     

Quantitation of gibberellins and the metabolism of [3H]gibberellin A1 during somatic embryogenesis in carrot and anise cell cultures

In a carrot (Daucus carota L.) cell line lacking the ability to undergo somatic embryogenasis, and in carrot and anise (Pimpinella anisum L.) cell lines in which embryogenesis could be regulated by presence or absence of 2,4-dichlorophen-oxyacetic acid (2,4-D), in the medium (+2,4-D=no embryogenesis,-2,4-D=embryo differentiation and development), the levels of endogenous gibberellin(s) (GA) were determined by the dwarfrice bioassay, and the metabolism of [³H]GA₁ was followed. Embryos harvested after 14 d of subculture in-2,4-D had low levels (0.2–0.3 g g^-1 dry weight) of polar GA (e.g. GA₁-like), but much (3–22 times) higher levels of less-polar GA (GA_4/7-like); GA₁, GA₄ and GA₇ are native to these cultures. Conversely, the undifferentiated cells in a non-embryogenic strain, and proembryos of an embryogenic strain (+2,4-D) showed very high levels of polar GA (2.9–4.4 g g^-1), and somewhat reduced levels of less-polar GA. Cultures of anise undergoing somatic embryo development (-2,4-D) metabolized [³H]GA₁ very quickly, whereas proembryo cultures of anise (+2,4-D) metabolized [³H]GA₁ slowly. The major metabolites of [³H]GA₁ in anise were tentatively identified as GA₈-glucoside (24%), GA₈ (15%), GA₁-glucoside (8%) and the ¹⁽¹⁰⁾GA₁-counterpart (2%). Thus, high levels of a GA₁-like substance and a reduced ability to metabolize GA₁ are correlated with the absence of embryo development, while lowered levels of GA₁-like substance and a rapid metabolism of GA₁ into GA₈ and GA-conjugates are correlated with continued embryo development. Exogenous application of GA₃ is known to reduce somatic embryogenesis in carrot cultures; GA₄ was found to have the same effect in anise cultures. Thus, a role (albeit negative) in somatic embryogenesis for a polar, biologically active GA is implied.Abbreviations 2,4-D 2,4-dichlorophenoxyacetic acid - GA gibberellin(s) or gibberellin-like substances - GC-RC gas chromatography-radiochromatogram counting - HPLC high-presare liquid chromatography - Rt retention time - TLC thinlaver chromatography     

Gibberellin physiology of safflower: endogenous gibberellins and response to gibberellic acid

Endogenous gibberellins (GAs) were extracted from safflower (Carthamus tinctorius L.) stems and detected by capillary gas chromatography-mass spectrometry from which GA₁, GA₃, GA₁₉,, GA₂₀, GA₂₉, and probably, GA₄₄ were detected. The detection of these GAs suggests that the early 13-OH biosynthetic pathway is prevalent in safflower shoots. Deuterated GAs were used as internal standards and GA concentrations were determined in stems harvested at weekly intervals. GA₁ and GA₁₉ levels per stem increased but concentrations per gram dry weight decreased over time. GA₂₀ was only detected in young stem tissue.Gibberellic acid (GA₃) was also applied in field trials and both GA₃ and the GA biosynthetic inhibitor, paclobutrazol, were applied in growth chamber tests. GA₃ increased epidermal cell size, internode length, and increased internode cell number causing stem elongation. Conversely, paclobutrazol reduced stem height, internode and cell size, cell number and overall shoot weight. In field tests, GA₃ increased total stem weight, but decreased leaf weight, flower bud number and seed yield. Thus, GA₃ promoted vegetative growth at the expense of reproductive commitment. These studies collectively indicate a promotory role of GAs in the control of shoot growth in safflower, and are generally consistent with gibberellin studies of related crop plants. Author for correspondence     

The quantitative relationship between gibberellin A1 and internode growth in Pisum sativum L.

The metabolism and growth-promoting activity of gibberellin A₂₀ (GA₂₀) were compared in the internode-length genotypes of pea, na le and na Le. Gibberellin A₂₉ and GA₂₉-catabolite were the major metabolites of GA₂₀ in the genotype na le. However, low levels of GA₁, GA₈ and GA₈-catabolite were also identified as metabolites in this genotype, confirming that the le allele is a leaky mutation. Gibberellin A₂₀ was approximately 20 to 30 times as active in promoting internode growth of genotype na Le as of genotype na le. However, the levels of the 3-hydroxylated metabolite of GA₂₀, GA₈ (2-hydroxy GA₁), were similar for a given growth response in both genotypes. In each case a close linear relationship was observed between internode growth and the logarithm of GA₈ levels. A similar relationship was found on comparing GA₂₀ metabolism in the three genotypes le ^d, le and Le. The former mutation results in a more severe dwarf phenotype than the le allele (which has previously been shown to reduce the 3-hydroxylation of GA₂₀ to GA₁). These results indicate that GA₂₀ has negligible intrinsic activity and support the contention that GA₁ is the only GA active per se in promoting stem growth in pea.Abbreviations GA_n gibberellin A_n - GC-MS gas chromatography-mass spectrometry - HPLC high-pressure liquid chromatography     

Persistence of 14C-gibberellin A3 on the surface of Citrus fruit peel and on inert glass surfaces

The persistence of gibberellin A₃ on plant surfaces was examined using fruit of Marsh seedless grapefruit (Citrus paradisi Macf.) and an inert glass model system. ¹⁴C-gibberellin A₃ was applied to surfaces in aqueous treatment solutions or in waxing solutions. Dried-out treatment residues were removed by washing and analyzed for total and GA₃-like radioactivity. Gibberellin A₃ persisted without significant loss for at least 7 d in aqueous treatment solutions (pH 4.0 or 6.2) but was less persistent in the pH 10.4 waxing solution (t1/2=7 d).Loss of total peel surface radioactivity was fast during the first 3 days, slowing down afterwards. After 14 days 73% of the initial radioactivity could still be recovered from fruit peel surface and 70% of the recovered radioactivity was still in the form of gibberellin A₃. Gibberellin A₃ was somewhat more persistent in residues from pH 4 than pH 7 treatment solutions. Light had a slight enhancing effect on gibberellin A₃ decomposition on fruit peel under growth chamber conditions. After 12 d at 100% relative humidity, 88% of the radioactivity on glass surfaces was still in the form of gibberellin A₃, as against 45% at a relative humidity of 50%. Simulated field conditions, combining daily fluctuations in light, temperature and relative humidity, markedly enhanced gibberellin A₃ decomposition on glass surfaces (t1/2=2 d). Gibberellin A₃ was very persistent (90% after 9 d) in the waxing residues on fruit peel surface.Abbreviations GA₃ gibberellin A₃ - RH relative humidity     

Synergistic promotion of gibberellin and cytokinin on direct regeneration of floral buds from in vitro cultures of sepal segments in sinningia speciosa hiern

Summary This study reports the direct regeneration of flower buds from cultured sepal segments of Sinningia speciosa Hiern. Two types of floral bud regeneration were observed: regeneration of floral buds only (designed as B^F) and regeneration of both floral and vegetative buds (designed as B^F+V). The capacity of B^F regeneration was closely related to the location of sepal segments and the concentration of exogenous gibberellin (GA₃) and cytokinin in the medium. On the medium containing 1.0mgl^−1 GA₃, the addition of 6-benzyladenine (BA) significantly increased the frequency of total flower bud (B^F+B^F+V) formation, with the frequency up to 91.5% in the presence of 0.4mgl^−1 BA. On the medium containing 0.1mgl^−1 BA, the addition of GA₃ also increased the frequency of total flower bud regeneration, with the frequency up to 74.3% in the presence of 1.0mgl^−1 GA₃, but no further increase in regeneration was observed when the GA₃ concentration was higher than 1.0mgl^−1. The capacity of B^F regeneration from different locations of sepal segments was differential. The adaxial part of sepal segments gave rise to the highest frequency of 56.7 and 84.3% for B^F and B^F+B^F+V, respectively.