Further studies on the metabolism of gibberellins (GAs) A9, A 20 and A 29 in immature seeds of Pisum sativum cv. progress No. 9.

Seed maturation of Pisum sativum cv. Progress No. 9 proceeds more slowly in winter than in summer even when the parent plants are grown in greenhouse conditions with light-and heat-supplementation. For parent plants grown under "summer" and "winter" conditions the metabolism of [(3)H]GA9 in cultured seeds is qualitatively different in seeds of equivalent age and qualitatively the same in seeds of equivalent weight. 13-Hydroxylation of [(3)H]GA9→[(3)H]GA20 is restricted to early stages of seed development. 2β-Hydroxylation of [(3)H]GA9→2β-OH-[(3)H]GA9 has only been observed at a stage of development after endogenous GA9 has accumulated. 2β-OH-GA9 has been shown to be endogenous to pea and is named GA51. H2-GA31 and its conjugate have not been shown to be present in pea and may be induced metabolites of [(3)H]GA9. The metabolism of GA20→GA29 is used to illustrate a technique of feeding [(2)H][(3)H]GAs in order to distinguish a metabolite from the same endogenous compound. The in vitro conversion of [(3)H]GA20→[(3)H]GA29, and the virtual non-metabolism of [(3)H]GA29 have been confirmed for seeds in intact fruits. These results are discussed in relation to the apparent absence of conjugated GAs in mature pea seeds.