Abstract
Gibberellin biosynthesis pathways were investigated using isotopically-labelled C19-and C20-gibberellins and cell-free preparations from immature seed of Phaseolus coccineus cv. Prizewinner. The initial steps in an early 13-hydroxylation pathway involved the conversion gibberellin A12-aldehyde (GA12-aldehyde) to GA12 which was 13-hydroxylated to yield GA53. Metabolism of GA53 yielded GA44. In contrast to other cell-free systems, GA44 was not further converted, either as a delta-lactone or an open-lactone structure, to the C-20 aldehyde GA19. GA19 was, however, metabolised to GA20, GA5 and GA1. GA20 represented a branch point in the pathway as it was converted both to GA1, which was an end product, and GA5 which was further converted to GA6. Like GA1, GA6 was also an end-product of the early 13-hydroxylation pathway.
A non-13-hydroxylation pathway involving GA4, GA15, GA24 GA37 and GA36 also originated from GA12. The terminal product of this pathway was the 3-beta-hydroxy C19-gibberellin, GA4.