The metabolism of gibberellins A9, A 20 and A 29 in immature seeds of Pisum sativum cv. Progress No. 9

Abstract

Gibberellin A9, GA20 and GA29, all known to be endogenous to immature seeds of Pisum sativum cv. Progress No. 9, were fed in tritiated form to seeds of this cultivar cultured in vitro. [(3)H]GA9 was metabolised to [(3)H]GA20, 2β-OH-[(3)H]GA9, H2-[(3)H]GA31 and a H2-[(3)H]GA31 conjugate. The percentage conversion to each metabolite varied from feed to feed but in each instance [(3)H]GA20 was, at most, a minor product, suggesting that in vivo GA9 may not be the principal precursor of GA20. [(3)H]GA20 was converted in very high yield to [(3)H]GA29 under conditions which suggest very strongly that this is a normal metabolic sequence in developing seeds of this cultivar. In addition, conjugates of [(3)H]GA20 and [(3)H] GA29 were formed in low yield. It was presumed that the latter was a metabolite of [(3)H]GA29. All metabolites, in each instance, were identified by combined gas chromatography-radiocounting and combined gas chromatography-mass spectrometry, and criteria for the unequivocal identification of radioactive products in feeds to plant tissues are put forward.