Floral initiation in sorghum hastened by gibberellic acid and far-red light

Combinations of far-red light (FR) (4 min) and gibberellic acid (GA₃), given at the beginning of a daily 12-h dark period in a growth room, were used to study floral induction in four maturity genotypes of the milo group of sorghum (Sorghum bicolor (L.) Moench). The 12-h dark period without GA₃ application or FR induced flowering in only the early genotype; FR hastened initiation in the early genotype, while GA₃ hastened floral initiation in the two intermidiate-flowering genotypes. GA₃ and FR together had a strong synergistic effect, hastening floral initiation by 30 to more than 80 d in the early and intermediate genotypes. Red light (R) did not hasten flowering; FR preceded by R gave the same effect as FR alone. GA₃ promoted stem elongation equally whether floral initiation occurred or not; thus, its effect on stem elongation was independent of floral initiation. The capacity of GA₃ to induce flowering in sorghum, a short-day plant, seems to be enhanced by phytochrome being in the P_R form at the beginning of the night when GA₃ was applied.Abbreviations FR far-red light - GA(s) gibberellin(s) - GA₃ gibberellic acid - R red light     

Studies on Flowering Responses of Urena lobata

Urena lobata L. is a qualitative short-day plant with a critical dark period of about 12 hr. A minimum of 12 short days are required for floral initiation. Gibberellic acid (GA₃) sprayed onto the leaves promoted flowering. The growth retardant, (2-chloroethyl)-trimethylammonium chloride (CCC) markedly inhibited flowering and stem elongation. This inhibition was reversed by subsequent application of GA₃.     

Exogenous GA<Subscript>3</Subscript> and flowering induce the conversion of artemisinic acid to artemisinin in <Emphasis Type="Italic">Artemisia annua</Emphasis> plants

The contents of artemisinin and artemisinic acid were monitored in the Artemisia annua plants treated with GA₃ at vegetative and flowering initiation stages. The highest artemisinin content was observed at full bloom. The decrease in artemisinic acid content occurred during the transition from the vegetative stage to the beginning of flowering. Endogenous GA₃ content in the leaves peaked at full bloom. At the vegetative stage, in plants treated with various concentrations of GA₃ , the content of artemisinin increased while that of artemisinic acid decreased. Apparently, the rate-limiting step in artemisinin biosynthesis was from artemisinic acid to artemisinin. The bottleneck of artemisinin biosynthesis was probably unlocked during the flowering or in the vegetative plants treated with GA₃ , which triggered off the conversion of artemisinic acid to artemisinin.From Fiziologiya Rastenii, Vol. 52, No. 1, 2005, pp. 68–73.Original English Text Copyright © 2005 by Zhang, Ye, Liu, Wang, Li.This article was presented by the authors in English.     

Floral induction by gibberellic acid in Impatiens balsamina,a qualitative short-day plant

Summary In the qualitative short-day plant Impatiens balsamina, gibberellic acid (GA₃) not only promoted the formation of floral buds in response to suboptimal photoinductive conditions and reduced the number of SD cycles that are required for their development into flowers, but also caused initiation of floral buds under non-inductive photoperiods. In plants treated with repeated applications of GA₃, the floral buds developed into flowers irrespective of whether the apex was left intact or was removed. In those that received a single application of GA₃ the floral buds developed into flowers only in decapitated plants.     

Flowering of Cultivated Green and SAN 9789-Treated Chenopodium rubrum Plants Exposed to White,Blue, and Red Light

Green plants and plants devoid of photosynthetic pigments were compared with regard to their ability to flower under various growth conditions. Green plants of Chenopodium rubrum L. and plants treated with norflurazon SANDOZ-9789 (SAN) were grown on sucrose-containing media with or without hormones (GA₃, BA, IAA, ABA) under short-day photoperiodic or continuous illumination with white, blue, or red light. Green and SAN-treated albino plants produced flowers only under short-day conditions. The flowering of green plants was independent of the presence of sucrose and hormones in the medium as well as of the light quality. The albino plants produced flowers under white and blue light but did not flower in red light. The addition of GA₃ or BA to the medium induced flowering of albino plants exposed to red light. The functional interaction of photoreceptors in the flowering control is discussed.     

The Interaction of Plant Growth Regulators and Vernalization on the Growth and Flowering of Cauliflower (Brassica oleracea var. botrytis)

The growth and flowering response of a cold-requiring cauliflower (Brassica oleracea var. botrytis cv. 60 day) to a range of temperatures under 10 h photoperiod and to growth regulator application were investigated. Endogenous gibberellin A₁(GA₁) concentrations were also assessed under these treatments. Flowering and growth of the inflorescence stalk were correlated with plant developmental stage at the time of a vernalizing cold treatment. Temperature and its duration also affected flowering and inflorescence development. The most effective temperature for inflorescence induction was 10 °C. Flowering did not occur in non-vernalized plants (25 °C) even though they had been treated with GA₃. Application of GA₃ promoted inflorescence stalk elongation greatly in vernalized plants (10 °C), but less so in partially vernalized plants (15 °C or 20 °C). Paclobutrazol (PP₃₃₃) sprayed at the 8–9 leaf stage significantly suppressed inflorescence stalk length and slightly delayed flower bud formation and anthesis. Vernalization at 10 °C increased endogenous GA₁ content in both leaves and the inflorescence stalk irrespective of GA₃ or PP₃₃₃ treatment. Application of GA₃ tended to increase GA₁ levels, while PP₃₃₃ significantly reduce GA₁, both irrespective of vernalization. Vernalization is an important factor for flowering, but not curd formation in this cauliflower cv. 60 day and GA₁ is likely a causal factor in inflorescence stalk elongation.     

GA3 induced flowering in Podophyllum hexandrum Royle: A rare alpine medicinal herb

Podophyllum hexandrum Royle, an important alpine herb, is the source of highly valued podophyllotoxin. The effect of some plant growth substances (GA₃, BAP & ABA), uniconazole (an inhibitor of GA biosynthesis), and a combination of GA₃ and uniconazole were examined in respect to influence on sprouting in rhizomes of P. hexandrum and on induction of flowering at a lower altitude. Amongst the various chemicals tested, GA₃ had a marked effect resulting in uniform sprouting and also induced flowering in about half of the treated rhizomes. While BAP also promoted early sprouting, delayed sprouting was seen in rhizomes treated with ABA. Uniconazole treatment, either alone or with GA₃ was found to inhibit flowering and also resulted in reduced plant height. GA₃ treatment of rhizomes from plants that was maintained for up to 30 months at a lower altitude also induced flowering thus replacing the normal chilling requirement of plants. These results suggest that treatment of GA₃ could be effectively used for inducing uniform sprouting and flowering in rhizomes of P. hexandrum grown at lower altitudes.     

The Effects of Growth Regulators on Flowering of Chenopodium murale Plants in vitro

In vitro culture of Chenopodium murale L. (ecotype 197) green and herbicide SAN 9789 - treated "white" plants was established and the effects of benzylaminopurine (BAP), indole-3-acetic acid (IAA) and gibberellic acid (GA₃) on growth and flowering were tested. Green plants did not flower on glucose free media, while 17 % of plants flowered on 5 % glucose-containing medium. SAN 9789 (10^–5 M) inhibited growth and flowering. BAP and IAA (0.1 – 5 mg dm^–3) also inhibited growth and flowering of green and "white" plants. GA₃ (10 mg dm^–3) stimulated leaf development in green plants, but had no significant effect on "white" plants, and stimulated flowering of green (41 %) and "white" (33 %) plants.     

Promotion of Flowering in Sagittaria pygmaea Miq. by 2,6-Diisopropylphenoxyacetic Acid

The flowering of Sagittaria pygmaea Miq. was promoted by 2,6-diisopropylphenoxyacetic acid, as well as by gibberellic acid (GA₃). Uniconazole canceled the promotive effect of the phenoxy-acetic acid, while prohexadione shortened the period required for flowering. Endogenous GAs seem to play an important role in the flowering of S. pygmaea, and 2,6-diisopropylphenoxyacetic acid might affect GA biosynthesis or metabolism.     

GA3和Spd对杜鹃开花期光合特性和抗氧化系统的影响

为探讨GA_3和Spd对杜鹃(Rhododendron simsii)开花花期和开花品质的影响,研究了外源GA_3和Spd对杜鹃开花期光合特性和抗氧化系统的变化。结果表明,外源GA_3对花期有显著的提前作用,Spd对花期有明显的延迟作用,但两者均使花期延长、花径增大且成花率提高。GA_3和Spd处理提高了花期叶片的光合色素含量和净光合速率(Pn)、气孔导度(Gs)和胞间CO_2浓度(Ci);GA_3处理提高了叶片的蒸腾速率(Tr),而Spd使叶片的Tr下降,两者均有效缓解了末花期叶绿素含量的下降。GA_3和Spd处理显著降低了花瓣MDA含量,提高了抗氧化酶SOD、POD和CAT活性,并减缓了末花期SOD的下降,有效延缓了衰老进程,延长花期。以1 600 mg L~(–1) GA_3和0.10 mmol L~(-1) Spd处理效果较好,能有效提高杜鹃花的观赏品质。     

Effect of Darkness on Growth and Flowering of Chenopodium rubrum and C. murale Plants in vitro

Chenopodium rubrum, a short-day plant, and C. murale, a long-day plant, were grown in vitro in continuous darkness. Control C. rubrum plants exposed to continuous darkness for 15 d at cotyledonary phase, did not flower, while 80 % of plants flowered on the medium with 5 % glucose and 10 mg dm⁻³ GA₃. Control C. murale plants exposed to continuous darkness for 10 d at the age of 4^th pair of leaves, did not flower, while GA₃ (1 – 5 mg dm⁻³) stimulated flowering up to 65 %. This revised version was published online in July 2006 with corrections to the Cover Date.     

Increased photosynthetic rates following gibberellic acid treatments to the roots of tomato plants

This study was conducted to evaluate the effects of root applications of gibberellic acid (GA₃) on photosynthesis in tomato plants grown hydroponically. Photosynthetic rates (mg CO₂/dm²/hr) determined using an open infrared CO₂ gas exchange system showed a 40–50% increase within 5 hr after treatment with a 1.4 µM gibberellic acid (GA₃) to their roots. The effect was shown to persist for the duration of the experiment (9 days). Plants receiving pulses of 1.4 µM GA₃ to the roots for 1, 4, 8 or 12 hr exhibited significantly higher photosynthetic rates than the control for 6 days following treatment. By day 9 however, there was no significant difference. Continual treatments with 1.4 µM GA₃ to the roots maintained the photosynthetic rate significantly higher than the control for the duration of the experiment. Interestingly, at the lower light levels the percent stimulation was more dramatic. There was approximately a 90% increase in the photosynthetic rate at 80 µE m^-2 s^-1 while at saturating light conditions (560 µE m^-2 s^-1) there was approximately a 40% increase over the control rate. The light saturation point for both treated and control plants was 240 µE m^-2 s^-1. Applications of physiologically relevant concentrations of GA₃ to the roots of tomato plants stimulates photosynthesis more consistently than that achieved by previous studies involving foliar absorption.Approved for publication on May 28, 1981 as paper number 6242 in the Journal series of the Pennsylvania Agricultural Experiment Station.     

Flowering of Chrysanthemum under non-inductive long days by gibberellins and N6-benzyladenine

Summary The flowering and inflorescence development of Chrysanthemum morifolium cv. Pink Champagne under non-inductive long days was promoted by exogenous application of GA₅, GA₃, GA₄+GA₇ or GA₉ in combination with the cytokinin, BA. The combination of BA and GA₅ was highly effective, BA and GA₃ moderately effective. Applications of the GAs alone or BA alone also resulted in some flowering, with GA₃ and GA₅ being most effective. In general, the effects of GA and BA were synergistic, and the concentration of both growth substances was a limiting factor with regard to the number of plants flowering under long days. Only the concentration of GA was a limiting factor for inflorescence development, however. Simultaneous application of indole-3-acetic acid reduced inflorescence development in most treatments. Development to the stage of anthesis was in no case effected.Abbreviations BA N⁶-benzyladenine - GA gibberellin - IAA indole-3-acetic acid This research was supported by National Research Council of Canada Grant No. 2585.     

Interactions between abscisic acid, ethylene and gibberellin in internodal elongation in floating rice: the promotive effect of abscisic acid at low humidity

The enhancement of internodal elongation in floating or deepwater rice (Oryza sativa L. cv. Habiganj Aman II) by treatment with ethylene or gibberellic acid (GA₃) at high relative humidity (RH) is inhibited by abscisic acid (ABA). Here, we examined the interactive effects of ethylene, gibberellin (GA) and ABA at low RH on internodal elongation of deepwater rice stem segments. Although ethylene alone hardly promoted internodal elongation of stem sections at 30% RH, it enhanced the internodal elongation induced by GA₃. Application of ABA alone to stem segments had no effect on internodal elongation. However, in the presence of ethylene and GA₃ at 30% RH, ABA further promoted internodal elongation. This promotive effect of ABA was not found in the internodes of stem segments treated either with ethylene or with GA₃ at 30% RH or in the internodes of stem segments treated with ethylene and/or GA₃ at 100% RH.     

Development of Seeded and Seedless Hypanthium of Rosa Canina After Application of Growth Substances

Dog rose (Rosa canina L.) plants in the bloom stages of flowering were sprayed by indole-3-acetic acid (IAA) in concentrations of 0.06 and 0.60 mM and gibberellic acid (GA₃) in concentrations of 0.60 and 1.50 mM. Ascorbic acid, total sugar, reducing sugar and carotenoid contents gradually increased, while the protein content remained unchanged and the content of phenolic substances decreased during hypanthium development. Ascorbic acid, total sugar, reducing sugar and carotenoid contents increased in hypanthium sprayed by GA₃ and IAA. However, IAA and GA₃ applications (except low concentrations) decreased contents of phenolic substances. IAA and GA applications might be a good way to produce the high quality hypanthium in R. canina.     

Gibberellic-acid causes flowering in the short-day plants Panicum miliaceum L., P. miliare lamk., and Setaria italica (L.) P. Beauv.

Treatment with gibberellic acid (GA₃) causes formation of flowers in Panicum ciliaceum and Panicum miliare, two short-day plants, under long days (continuous light), and hastens the emergence of ears in Setaria italica, a quantitative short-day plant, under both inductive and non-inductive photoperiods. The GA₃-induced inflorescences, however, remain short and bear only few spikelets; in the two Panicum species, the spikelets also remain sterile.     

New perspectives of gibberellic acid production: a review

The gibberellins (GAs) are an important group of hormones which exert various effects on promoter and regulator of plant growth. Gibberellic acid (GA₃) is a natural plant hormone, with great economical and industrial importance. It affects stem elongation, germination, elimination of dormancy, flowering, sex expression, enzyme induction and leaf and fruit senescence. Despite its diverse applications, the use of GA₃ is limited due to its high production costs. The industrial process currently used for the production of GA₃ is based on submerged fermentation (SmF) techniques. As an alternative for its production, solid state fermentation (SSF) has also been investigated for its ability to increase the yields of GA₃ with the use of agro-industrial wastes as support/substrate, which contributes to the decreased production costs. This review describes GA₃’s physical, chemical and biological properties, its production by fermentation and new advances that are being carried out with special interest on the SSF technique.     

Effects of root applications of gibberellic acid on photosynthesis and growth in C3 and C4 plants

The effects of root applications of gibberellic acid (GA₃) on growth and photosynthesis of 12 species of plants including C₃ monocots (Triticum aestivum L., wheat, Hordeum vulgare L., barley and Avena sativa L., oat), C₃ dicots (Vigna radiata L., mung bean, Cucurbita moschata L., squash and Capsicum annuum L., pepper), C₄ monocots (Zea mays L., corn, Sorghum vulgare L., sorghum and Panicum ramosum L., millet) and C₄ dicots (Amaranthus retroflexus L., pigweed, Kochia scoparis L., kochia and Gomphrena celosoides L., gomphrena) were evaluated. Relative growth rates (RGR) of barley, oat, squash, pepper, corn, sorghum, millet, pigweed and kochia were increased above the control by 12.7%, 9.9%, 11.3%, 10.7%, 19.2% 10.1%, 11.5%, 16.4% and 32.7% respectively, four days following optimum GA₃ treatments. There was no effect of GA₃ on RGR in wheat, mung bean, and gomphrena. Gibberellic acid decreased the chlorophyll content expressed on an area basis by 20.0%, 13.9%, 20.9%, 17.1%, 11.9% and 28.0% in barley, squash, pepper, sorghum, pigweed and kochia, respectively, while that of oat, wheat, mung bean, corn, millet and gomphrena remained unchanged. When photosynthetic rates were expressed per mg of chlorophyll, it showed that GA₃ could stimulate photosynthesis in barley, squash, pepper, sorghum, millet, pigweed and kochia by 20.4%, 20.6%, 16.5%, 17.4%, 10.4%, 24.2%, and 29.4%; while there was no effect in oat, wheat, mung bean, corn and gomphrena. An increase in leaf blade area and/or length of sheath were observed in GA₃ treated plants of oat, barley, mung bean, squash, pepper, corn, sorghum, millet and kochia. The transpiration rate remained unchanged following GA₃ treatment in all 12 species.This work was supported in part by the Fair Funds administered by the Pennsylvania Department of Agriculture. Contribution No. 39, Department of Horticulture, The Pennsylvania State University. Authorized for publications as paper no. 6886 in the journal series of the Pennsylvania Agricultual Experiment Station.Research assistant and assistant professor respectively.     

Promotion of flowering in the Pinaceae by gibberellins

Significant female flowering of 6- to 11-year-old seedlings and grafted ramets of sexually mature scions of lodgepole pine (Pinus contorta Dougl.) was promoted by both topical and spray applications of a gibberellin (GA) A_4/7 mixture (1.6 to c. 5 mg per plant in total) during that period (June to September) when sexual differentiation of lateral primordia would be expected to take place. Girdling was used in most experiments to enhance the GA_4/7 effect, as was the auxin, naphthaleneacetic acid (NAA). Average frequency of flowering branches on treated plants over all experiments ranged from 27 to 59% (control ranged from 0 to 36%) and average number of female strobili was increased from 2- to 6-fold by growth regulator treatment, relative to controls. Within an experiment, clonal or family frequency of flowering for treated plants ranged from 11 to 67% (controls were 0 to 28%), and number of female strobili was increased from 2- to 14-fold by growth regulator treatment, relative to controls. Movement of the flowering stimulus from the point of application was apparent in several experiments, the response in adjacent branches being correlated positively with increasing dosage of GA_4/7. Significant male flowering occurred only in one experiment, girdling and GA_4/7 treatment being promotive factors. The use of spray applications of GA_4/7+ NAA is warranted to induce early and enhanced flowering in lodgepole pine seedlings and vegetative propagules for genetic improvement programs.     

Responses of ivy (Hedera helix L.) to combinations of gibberellic acid,paclobutrazol and abscisic acid

A reduction in concentration of gibberellins has been implicated in the phase change from juvenile to mature forms of ivy (Hedera helix L.). Attempts were made to increase the effective internal concentration of gibberellins by exogenous application of GA₃, and to decrease them by various applications of abscisic acid (ABA) and paclobutrazol (PP333), alone or in combination with GA₃. ABA and GA₃ were fed directly into the xylem of ivy plants by a wick system (a less drastic procedure than the defoliation or decapitation used by earlier workers) whereas PP333 was applied as a soil drench.Mature ivy responded to the application of GA₃ by reversion to the juvenile form, although this reversion was incomplete with respect to leaf lobing and red (anthocyanin) pigmentation and could occur spontaneously without the application of GA₃. Contrary to expectation, applications of ABA and PP333 caused the stimulation of growth in juvenile ivy. No adult characteristics were induced. As similar concentrations of ABA and PP333 produced severe retardation of growth (which could be alleviated by the application of GA₃) in other species, it is suggested that ivy may be an unsuitable model system for the investigation of phase change in woody plants.