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.