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.

The elongation response of the gibberellin (GA) deficient genotypes na, Is, and lh of peas (Pisum sativum L.) to a range of GA-precursors was examined. Plants possessing gene na did not respond to precursors in the GA biosynthetic pathway prior to GAj2-aldehyde. In contrast, plants possessing Ih and Is responded as well as wild-type plants (dwarfed with AMO-1618) to these compounds. The results suggest that GA biosynthesis is blocked prior to ent-kaurene in the Ih and Is mutants and between ent-7a-hydroxykaurenoic acid and GAi2-aldehyde in the na mutant. Feeds of ent-VIHlkaurenoic acid and I2HJGAi2-aldehyde to a range of genotypes supported the above conclusions. The na line WL1766 was shown by gas chromatography-mass spectrometry (GC-MS) to metabolize [2HjGA12-aldehyde to a number of 12H1C19-GAs including GA,.However, there was no indication in na genotypes for the metabolism of ent-VIH-kaurenoic acid to these GAs. In contrast, the expanding shoot tissue of all Na genotypes examined metabolised ent-VHjkaurenoic acid to radioactive compounds that co-chromatographed with GA,, GA,, GA2, and GA29. However, insufficient material was present for unequivocal identification of the metabolites. The radioactive profiles from HPLC of extracts of the node treated with ent-[H]kaurenoic acid were similar for both Na and na plants and contained ent-16a,17-dihydroxykaurenoic acid and ent-6a,7a,16,,17-tetrahydroxykaurenoic acid (both characterized by GC-MS), suggesting that the metabolites arose from side branches of the main GA-biosynthetic pathway. Thus, both Na and na plants appear capable of ent-7a-hydroxylation.

The influence of the Na and Le genes in peas on gibberellin (GA) levels and metabolism were examined by gas chromatographic-mass spectrometric analysis of extracts from a range of stem-length genotypes fed with [(13)C, (3)H]GA20. The substrate was metabolised to [(13)C, (3)H]GA1, [(13)C, (3)H]GA8 and [(13)C, (3)H]GA29 in the immature, expanding apical tissue of all genotypes carrying Le. In contrast, [(13)C, (3)H]GA29 and, in one line, [(13)C, (3)H]GA29-catabolite, were the only products detected in plants homozygous for the le gene. These results confirm that the Le gene in peas controls the 3β-hydroxylation of GA20 to GA1. Qualitatively the same results were obtained irrespective of the genotype at the Na locus. In all Na lines the [(13)C, (3)H]GA20 metabolites were considerably diluted by endogenous [(12)C]GAs, implying that the metabolism of [(13)C, (3)H]GA20 mirrored that of endogenous [(12)C]GA20. In contrast, the [(13)C, (3)H]GA20 metabolites in na lines showed no dilution with [(12)C]GAs, confirming that the na mutation prevents the production of C19-GAs. Estimates of the levels of endogenous GAs in the apical tissues of Na lines, made from the (12)C:(13)C isotope ratios and the radioactivity recovered in respective metabolites, varied between 7 and 40 ng of each GA per plant in the tissue expanded during the 5 d between treatment with [(13)C, (3)H]GA20 and extraction. No [(12)C]GA1 and only traces of [(12)C]GA8 (in one line) were detected in the two Na le lines examined. These results are discussed in relation to recent observations on dwarfism in rice and maize.

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.