GA1 Concentrations Research Articles

Vernalization and Gibberellin Physiology of Winter Canola (Endogenous Gibberellin (GA) Content and Metabolism of [3H]GA1 and [3H]GA20.

Winter canola (Brassica napus cv Crystal) is an oilseed crop that requires vernalization (chilling treatment) for the induction of stem elongation and flowering. To investigate the role of gibberellins (GAs) in vernalization-induced events, endogenous GA content and the metabolism of [3H]GAs were examined in 10-week vernalized and nonvernalized plants. Shoot tips were harvested 0, 8, and 18 d postvernalization (DPV), and GAs were purified and quantified using 2H2-internal standards and gas chromatography-selected ion monitoring. Concentrations of GA1, GA3, GA8, GA19, and GA20 were 3.1-, 2.3-, 7.8-, 12.0-, and 24.5-fold higher, respectively, in the vernalized plants at the end of the vernalization treatment (0 DPV) relative to the nonvernalized plants. Thermoregulation apparently occurs prior to GA19 biosynthesis, since vernalization elevated the concentration of all of the monitored GAs. [3H]GA20 or [3H]GA1 was applied to the shoot tips of vernalized and nonvernalized plants, and after 24 h, plants were harvested at 6, 12, and 15 DPV. Following high-performance liquid chromatography analyses, vernalized plants showed increased conversion of [3H]GA20 to a [3H]GA1-like metabolite and reduced conversion of [3H]GA1 or [3H]GA20 to polar 3H-metabolites, putative glucosyl conjugates. These results demonstrate that vernalization influences GA content and GA metabolism, with GAs serving as probable regulatory intermediaries between chilling treatment and subsequent stem growth.

Gibberellic acid decreases anthocyanin accumulation in wild carrot cell suspension cultures but does not alter 3′‐nucleotidase activity

Gibberellic acid (GA3) applied at different times during the growth of wild carrot (Daucus carota ssp. Carota) cell suspension cultures inhibited anthocyanin accumulation. Application of 3 × 10–6M GA3 to cultures on day 0 or day 4 gave, respectively, 10 or 35% of anthocyanin accumulation relative to levels occurring when GA3 was applied at the end of the growth period. Endogenous GAs were separated by high pressure liquid chromatography, and identified and quantified by gas chromatography‐selected ion monitoring. Gibberellins GA1, GA3 and traces of GA8. GA19 and GA20 were identified in carrot cell suspension cultures of both high and low anthocyanin‐accumulating clones. The concentrations of GA1. GA3 and GA8 in the two clones were similar and were not significantly different after the application of uniconazole which promoted anthocyanin accumulation. This suggests that these endogenous GAs are not the sole factors controlling the accumulation of anthocyanin in these different clones. Exogenous GA3 and uniconazole had no effect on 3′‐nucleotidase and 5′‐nucleotidase activity in the carrot cell suspension cultures. Thus 3′‐nucleotidase does not appear to play a role in the inhibition of anthocyanin accumulation by exogenous GA3.

Analysis of gibberellins in growing fruits ofLycopersicon esculentumafter pollination or treatment with 4-chlorophenoxyacetic acid

SummaryIdentification and quantification of gibberellins (GAs) were conducted in tomato pistils (Lycopersicon esculentum Miller) two days before anthesis as well as in pollinated fruits and parthenocarpic fruits induced by 4-chlorophenoxyacetic acid (4-CPA) treatment at 1, 3,6,10 and 14 d after anthesis. GA1, GAg, GA17, GA19, GA20, GA29 and GA44 were identified by combined gas chromatography-mass spectrometry (GC-MS) in pollinated fruits and parthenocarpic fruits; pollinated fruits in addition contained GA9, GA15, GA24 and GA25. 2 β-OH-GA53 was also tentatively identified in both types of fruits. Activity of GAs could not be detected in emasculated pistils. In the early stage of growth of pollinated fruits between 1 and 6 d after anthesis, the biosynthetic pathway to the C20-GA precursor of GA1, GA19, was much more accelerated than in parthenocarpic fruits, indicating that pollination may stimulate the pathway more strongly than 4-CPA. Parthenocarpic fruit tissues had a much higher concentration of GA1 than those from pollinated fruits at 10-14 d after anthesis, indicating that higher levels of GA1 may correlate with the size of fruit, because larger fruit was associated with parthenogenesis in the early stage of fruit growth. In pollinated fruits, the concentration of G A20 was much higher than that of GA1, indicating that 3 β-hydroxylation of GA20 may be a limiting step in GA1 biosynthesis for pollinated fruit growth.

Distribution of endogenous gibberellins in vegetative and reproductive organs of Brassica

Recognizing the physiological diversity of different plant organs, studies were conducted to investigate the distribution of endogenous gibberellins (GAs) in Brassica (canola or oilseed rape). GA1 and its biosynthetic precursors, GA20 and GA19, were extracted, chromatographically purified, and quantified by gas-chromatography-selected ion monitoring (GC-SIM), using [2H2]GAs as internal standards. In young (vegetative) B. napus cv. Westar plants, GA concentrations were lowest in the roots, increased acropetally along the shoot axis, and were highest in the shoot tips. GA concentrations were high but variable in leaves. GA1 concentrations also increased acropetally along the plant axis in reproductive plants. During early silique filling, GA1 concentrations were highest in siliques and progressively lower in flowers, inflorescence stalks (peduncles plus pedicels), stem, leaves, and roots. Concentrations of GA19 and GA20 showed similar patterns of distribution except in leaves, in which concentrations were higher, but variable. Immature siliques were qualitatively rich in endogenous GAs and GA1, GA3, GA4, GA8, GA9, GA17, GA19, GA20, GA24, GA29, GA34, GA51, and GA53 were identified by GC-SIM. In whole siliques, GA19, GA20, GA1, and GA8 concentrations declined during maturation due to declining levels in the maturing seeds; their concentrations in the silique coats remained relatively constant and low. These studies demonstrate that GAs are differentially distributed in Brassica with a general pattern of acropetally increasing concentration in shoots and high concentration in actively growing and developing organs.

Gibberellins and Heterosis in Sorghum

Two triplet combinatioas of sorghum, [Sorghum bicolor (L.) Moench], each consisting of two homozygous parental lines and their F1 hybrid (ATx623 × Hegaria; ATx378 × RTx430), were grown in controlled environment chambers to examine the possible relationship between gibberellins (GAs) and heterosis (hybrid vigor). Heterosis for shoot growth occurred as shoot dry weights and leaf areas were greater in the hybrids than in parental inbreds. The exogenous application of 0.1, 0.5, or 1.0 mg GA3 by pipetting into the leaf whorl promoted leaf sheath and leaf blade elongation in all genotypes. GA3 also promoted shoot dry weight and/or leaf area in three of the four inbreds, but hybrids were relatively unaffected. Endogenous GA1 was measured by gas chromatography‐selected ion monitoring, using [2H2]GA1 as an internal standard. At one of the two harvests (Day 22 and 29) for each triplet, the hybrid contained significantly higher concentrations of GA1 than either parent. Endogenous GA3 was characterized by GC‐SIM in samples, from the second harvest and showed the same pattern as GA1. Thus, at some stages, these sorghum inbreds apparently have a partial deficiency of endogenous GA. The response to exogenous GA3 application suggests that the GA deficiency is a limitation to their growth. Thus, GAs are apparently involved in heterosis for shoot growth in sorghum.

Dwarf mutants ofBrassica: Responses to applied gibberellins and gibberellin content

Eight rapid-cyclingBrassica genotypes differing in height were treated with gibberellins (GAs) by syringe application to the shoot tip. The height of two genotypes ofBrassica napus, Bn5-2 and Bn5-8, andB. rapa mutants,dwarf 1 (dwf1) anddwarf 2 (dwf2), was unaffected by exogenous GA3 at dosages up to 0.1 μg/plant, a level which increased shoot elongation of normal genotypes. Thus, these dwarf mutants are “GA-insensitive.” In contrast to theB. napus dwarfs, twoB. rapa mutants,rosette (ros), anddormant (dor), elongated following GA3 application. The dwarfros was most sensitive, responding to applications as low as 1 ng GA3/plant. Furthermore,ros also responded to GA1 and some of its precursors with decreasing efficacy: GA3>ent-kaurenoic acid ≥GA1>GA20≥GA19=GA44≥GA53. Endogenous GAs were measured by gas chromatography-selected ion monitoring using [2H2]GA internal standards for calibration, from shoots of the GA-insensitive genotypes Bn5-2, Bn5-8 which contained theB. napus mutantdwarf 1, and from a normal genotype Bn5-1. Concentrations of GA1 and GA20 averaged 3.2- and 4.6-fold higher, respectively, and GA19 levels also tended to be higher in the dwarfs than in the normal genotype.

Identification, quantitation and distribution of gibberellins in fruits of Pisum sativum L. cv. Alaska during pod development

In addition to the previously-reported gibberellins: GA1; GA8, GA20 and GA29 (García-Martínez et al., 1987, Planta 170, 130-137), GA3 and GA19 were identified by combined gas chromatography-mass spectrometry in pods and ovules of 4-d-old pollinated pea (Pisum sativum cv. Alaska) ovaries. Pods contained additionally GA17, GA81 (2α-hydroxy GA20) and GA29-catabolite. The concentrations of GA1, GA3, GA8, GA19, GA20 and GA29 were higher in the ovules than in the pod, although, with the exception of GA3, the total content of these GAs in the pod exceeded that in the seeds. About 80% of the GA3 content of the ovary was present in the seeds. The concentrations of GA19 and GA20 in pollinated ovaries remained fairly constant for the first 12 ds after an thesis, after which they increased sharply. In contrast, GA1 and GA3 concentrations were maximal at 7 d and 4-6 d, respectively, after anthesis, at about the time of maximum pod growth rate, and declined thereafter. Emasculated ovaries at anthesis contained GA8, GA19 and GA20 at concentrations comparable with pollinated fruit, but they decreased rapidly. Gibberellins a1 and A3 were present in only trace amounts in emasculated ovaries at any stage. Parthenocarpic fruit, produced by decapitating plants immediately above an emasculated flower, or by treating such flowers with 2,4-dichlorophenoxyacetic acid or GA7, contained GA19 and GA20 at similar concentrations to seeded fruit, but very low amounts of GA1 and GA3 Thus, it appears that the presence of fertilised ovules is necessary for the synthesis of these last two GAs. Mature leaves and leaf diffusates contained GA1, GA8, GA19 and GA20 as determined by combined gas chromatography-mass spectrometry using selected ion monitoring. This provides further evidence that vegetative tissues are a possible alternative source of GAs for fruit-set, particularly in decapitated plants.

Gibberellins inCitrus sinensis: A comparison between seeded and seedless varieties

The gibberellin (GA) content of the reproductive organs ofCitrus sinensis (L.) Osb., cv. Bianca Comuna and the seedless variety, Salustiana, were examined by combined gas chromatography-mass spectrometry (GC/MS) at different stages of development. Gibberellins A1, A20, and A29 were identified in the reproductive buds of both cultivars 21 days prior to anthesis and in fruits 35 days after anthesis by comparison of their mass spectra and Kovats retention indices with those of standards. In addition, three uncharacterized isomers of GA1 were detected, one in buds and two in fruits. The presence of GA4 in both tissues, and of GA8 in the reproductive buds, was indicated by the occurrence of characteristic ions at the expected retention times, although their spectra were too weak for full identification. Vegetative shoots of cv. Salustiana contained gibberellins A1, A19, A20, and A29, and the unidentified isomer of GA1 present in reproductive buds. The presence of trace amounts of gibberellins A8 and A17 was also indicated. Although the two varieties did not differ qualitatively in the GAs present during flower and fruit development, the seedless variety contained slightly greater amounts. The concentrations of gibberellins A1, A4, and A20 were determined by gas chromatography-selected ion monitoring (GC/SIM) throughout ovary development and early fruit growth. In both varieties, the maximum GA1 concentration occurred at anthesis. Highest concentrations of gibberellins A20 and A4 were found in fruit 35 days after anthesis, although the GA1 concentration at this stage remained low.

Gibberellins and Heterosis in Maize: Quantitative Relationships

To investigate the possible relationship between gibberellins (GA) and heterosis, a diailel from four elite maize, Zea mays L., inbreds (A632, B73, CH807 [from Mo17], and CO109) was studied under controlled environment conditions. Heterosis for plant growth was substantial at 25/15 °C (day/night), as hybrid seedlings emerged more rapidly, were taller, had heavier shoots, and larger leaf areas than the parental inbreds. Gibberellic acid (GA3) at 0.1, 0.5, or 1.0 mg per plant was pipetted into the leaf whorls of 14‐d‐old seedlings. The exogenous GA3 promoted ligule and total height in all genotypes, but the inbreds were maximally influenced. Consequently, potence ratios, representing the overall degree of dominance, were reduced from an average of 7.7 to 1.7 following GA3 application, indicating decreased heterosis. In an experiment at 15 °C, imbibition of seeds in GA3 accelerated germination and seedling growth, particularly shoot elongation of the parental inbreds. Endogenous concentrations of GA1 and GA19 were determined by gas‐chromatography‐selected ion monitoring using [2H]GAs as quantitive internal standards. Highly significant regressions of height, leaf area, relative growth rate, and height increment versus the log of GA concentration were observed. These results are consistent with the theory that GA are one factor involved in the regulation of heterosis of shoot growth in maize, a theory that suggests that a partial deficiency in endogenous GA in maize inbreds limits their growth, and is a contributing cause of inbreeding depression.

Identification and quantitation of gibberellins in fruits of Lycopersicon esculentum, and their relationship to fruit size in L. esculentum and L. pimpinellfolium

GA1, GA8, GA17, GA19, GA20 and GA29 were identified by combined gas chromatography‐mass spectrometgry (GC‐MS) in immature seeds and pericarp of Lycopersicon esculentum Mill. (tomato). Higher levels of these GAs were present in the seeds than in the pericarp; seeds in addition contained GA15, GA24, GA25, and GA44. Fruits of the Lycopersicon pimpinellifolium Mill. mutant I were smaller and contained lower GA1 concentrations, but higher GA20 concentrations, than those of mutants III and IV. In contrast, differences in fruit size in L. esculentum due to position on the truss did not correlate with GA1 concentration in either the pericarp or seeds.