Gibberellins in immature seeds and dark-grown shoots of Pisum sativum : Gibberellins identified in the tall cultivar Alaska in comparison with those in the dwarf Progress No. 9

On the hormonal nature of the stimulatory effect of high incubation temperatures on germination of dormant sorghum (S. bicolor) caryopses

•  High incubation temperatures (i.e. 30°C) stimulate the germination of dormant sorghum grains. To test the hormonal nature of this response, experiments were carried out with two varieties with contrasting dormancy at harvest: Redland B2 (low dormancy, high germination percentages attained under a wide incubation thermal range) and IS 9530 (high dormancy, high germination percentages attained only at 30°C). •  Redland B2 grains with reduced GA content (paclobutrazol-treated) reached high germination temperatures (c. 100%) only when incubated at 30°C. By contrast, IS 9530 grains with reduced ABA content (fluridone-treated) reached 100% germination at 30, 25, 20 and 15°C. •  Incubation temperatures did not alter embryo responsiveness to ABA, nor did it modify the pattern of changes in embryo ABA content throughout incubation. Low GA₃ concentrations (0.1 µm) were required to totally overcome the inhibition imposed by ABA in embryos incubated at 30°C; by contrast, even the highest GA₃ concentrations used (1000 µm) were not able to revert ABA inhibition in embryos incubated at 15°C. •  These results show the hormonal nature of the stimulatory effect of high incubation temperatures, and suggest that this effect is mediated by an increase in tissue responsiveness to GAs.

The source of gibberellins in the parthenocarpic development of ovaries on topped pea plants

The role and source of gibberellins (GAs) involved in the development of parthenocarpic fruits of Pisum sativum L. has been investigated. Gibberellins applied to the leaf adjacent to an emasculated ovary induced parthenocarpic fruit development on intact plants. The application of gibberellic acid (GA3) had to be done within 1 d of anthesis to be fully effective and the response was concentration-dependent. Gibberellin A1 and GA3 worked equally well and GA20 was less efficient. [(3)H]Gibberellin A1 applied to the leaf accumulated in the ovary and the accumulation was related to the growth response. These experiments show that GA applied to the leaf in high enough concentration is translocated to the ovary. Emasculated ovaries on decapitated pea plants develop without application of growth hormones. When [(3)H] GA1 was applied to the leaf adjacent to the ovary a substantial amount of radioactivity accumulated in the growing shoot of intact plants. In decapitated plants, however, this radioactivity was mainly found in the ovary. There it caused growth proportional to the accumulation of CA1. Application of LAB 150978, an inhibitor of GA biosynthesis, to decapitated plants inhibited parthenocarpic fruit development and this inhibition was counteracted by the application of GA3 (either to the fruit, or the leaf adjacent to the ovary, or through the lower cut end of the stem). All evidence taken together supports the view that parthenocarpic pea fruit development on topped plants depends on the import of gibberellins or their precursors, probably from the vegetative aerial parts of the plant.

Gibberellins in developing fruits of Pisum sativum cv. Alaska: Studies on their role in pod growth and seed development

Gibberellins A1, A8, A20 and A29 were identified by capillary gas chromatography-mass spectrometry in the pods and seeds from 5-d-old pollinated ovaries of pea (Pisum sativum cv. Alaska). These gibberellins were also identified in 4-d-old non-developing, parthenocarpic and pollinated ovaries. The level of gibberellin A1 within these ovary types was correlated with pod size. Gibberellin A1, applied to emasculated ovaries cultured in vitro, was three to five times more active than gibberellin A20. Using pollinated ovary explants cultured in vitro, the effects of inhibitors of gibberellin biosynthesis on pod growth and seed development were examined. The inhibitors retarded pod growth during the first 7 d after anthesis, and this inhibition was reversed by simultaneous application of gibberellin A3. In contrast, the inhibitors, when supplied to 4-d-old pollinated ovaries for 16 d, had little effect on seed fresh weight although they reduced the levels of endogenous gibberellins A20 and A29 in the enlarging seeds to almost zero. Paclobutrazol, which was one of the inhibitors used, is xylem-mobile and it efficiently reduced the level of seed gibberellins without being taken up into the seed. In intact fruits the pod may therefore be a source of precursors for gibberellin biosynthesis in the seed. Overall, the results indicate that gibberellin A1, present in parthenocarpic and pollinated fruits early in development, regulates pod growth. In contrast the high levels of gibberellins A20 and A29, which accumulate during seed enlargement, appear to be unnecessary for normal seed development or for subsequent germination.

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 3β-hydroxylated metabolite of GA20, GA8 (2β-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 3β-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.

Gibberellins in dark- and red-light-grown shoots of dwarf and tall cultivars of Pisum sativum: The quantification, metabolism and biological activity of gibberellins in Progress no. 9 and Alaska

The stem growth in darkness or in continuous red light of two pea cultivars, Alaska (Le Le, tall) and Progress No. 9 (le le, dwarf), was measured for 13 d. The lengths of the first three internodes in dark-grown seedlings of the two cultivars were similar, substantiating previous literature reports that Progress No. 9 has a tall phenotype in the dark. The biological activity of gibberellin A20 (GA20), which is normally inactive in le le geno-types, was compared in darkness and in red light. Alaska seedlings, regardless of growing conditions, responded to GA20. Dark-grown seedlings of Progress No. 9 also responded to GA20, although red-light-grown seedlings did not. Gibberellin A1 was active in both cultivars, in both darkness and red light. The metabolism of [(13)C(3)H]GA20 has also been studied. In dark-grown shoots of Alaska and Progress No. 9 [(13)C(3)H]GA20 is converted to [(13)C(3)H]GA1, [(13)C(3)H]GA8, [(13)C]GA29, its 2α-epimer, and [(13)C(3)H]GA29-catabolite. [(13)C(3)H] Gibberellin A1 was a minor product which appeared to be rapidly turned over, so that in some feeds only its metabolite, [(13)C(3)H]GA8, was detected. However results do indicate that the tall growth habit of Progress No. 9 in the dark, and its ability to respond to GA20 in the dark may be related to its capacity to 3β-hydroxylate GA20 to give GA1. In red light the overall metabolism of [(13)C(3)H]GA20 was reduced in both cultivars. There is some evidence that 3β-hydroxylation of [(13)C(3)H]GA20 can occur in red light-grown Alaska seedlings, but no 3β-hydroxylated metabolites of [(13)C(3)H]GA20 were observed in red light-grown Progress. Thus the dwarf habit of Progress No. 9 in red light and its inability to respond to GA20 may be related, as in other dwarf genotypes, to its inability to 3β-hydroxylate GA20 to GA1. However identification and quantification of native GAs in both cultivars showed that red-light-grown Progress does contain native GA1. Thus the inability of red light-grown Progress No. 9 seedlings to respond to, and to 3β-hydroxylate, applied GA20 may be due to an effect of red light on uptake and compartmentation of GAs.

Internode length in Pisum sativum L. The kinetics of growth and [(3)H]gibberellin A 20 metabolism in genotype na Le

The relationship between shoot growth and [(3)H]gibberellin A20 (GA20) metabolism was investigated in the GA-deficient genotype of peas, na Le. [17-(13)C, (3)H2]gibberellin A20 was applied to the shoot apex and its metabolic fate examined by gas chromatographic-mass spectrometric analysis of extracts of the shoot and root tissues. As reported before, [(13)C, (3)H2]GA1, [(13)C, (3)H2]GA8 and [(13)C, (3)H2]GA29 constituted the major metabolites of [(13)C, (3)H2]GA20 present in the shoot. None of these GAs showed any dilution by endogenous (12)C-material. [(13)C, (3)H2]GA29-catabolite was also a prominent metabolite in the shoot tissue but showed pronounced isotope dilution probably due to carry-over of endogenous [(12)C]GA29-catabolite from the mature seed. In marked contrast to the shoot tissue, the two major metabolites present in the roots were identified as [(13)C, (3)H2]GA8-catabolite and [(13)C, (3)H2]GA29-catabolite. Both of these compounds showed strong dilution by endogenous (12)C-material. Only low levels of [(13)C, (3)H2]GA1, [(13)C, (3)H2]GA8, [(13)C, (3)H2]GA20 and [(13)C, (3)H2]GA29 accumulated in the roots. It is suggested that compartmentation of GA-catabolism may occur in the root tissue in an analogous manner to that shown in the testa of developing seeds. Changes in the levels of [1β,3α-(3)H2]GA20 metabolites over 10 d following application of the substrate to the shoot apex of genotype na Le confirmed the accumulation of [(3)H]GA-catabolites in the root tissues. No evidence was obtained for catabolic loss of [(3)H]GA20 by complete oxidation or conversion to a methanol-inextractable form. The results indicate that the root system may play an important role in the regulation of biologically active GA levels in the developing shoot of Na genotypes of peas.