Metabolism of gibberellin A29 in seeds of Pisum sativum cv. Progress No. 9; Use of [2H] and [3H]GAs, and the identification of a new GA catabolite

Abstract

The metabolism of GA29 in maturing seeds of Pisum sativum cv. Progress No. 9 was further investigated, and the utility of (2)H-labelled GAs in conjuction with GC-MS is illustrated. Using [2α-(2)H1]GA29 as an internal standard, endogenous GA29 was shown to reach a maximal level (ca. 10 μg/seed) 27 days from anthesis, and to decline to ca. 1.6 μg/seed in mature seeds. In a time-course feed the metabolism of [2α-(2)H1] [2α-(3)H1]GA29 applied to 27 day old seeds, and of endogenous GA29, was compared from the (1)H:(2)H ratios in the recovered GA29. Although both [2α-(2)H1] [2α-(3)H1]GA29 and endogenous GA29 were metabolised to the same limited extent to a putative conjugate, in the main metabolic process endogenous GA29 was preferentially converted to an untraceable (i.e. unlabelled) metabolite. In contrast, endogenous GA29 and [1β,3α-(2)H2] [1β,3α-(3)H2]GA29, derived from [1β,3α-(2)H2] [1β,3α-(3)H2]GA20 in a time-course feed, were metabolised in an identical manner. In the latter case isotope loss precluded identification of the metabolite. The structure (8) has been assigned to a GA catabolite present in maturing seeds and seedlings of pea. The isotope data are consistent with this compound being the hitherto untraced metabolite of GA29 in pea.