Metabolism of [(13)C 1]gibberellin A 29 to [ (13)C 1]gibberellin-catabolite in maturing seeds of Pisum sativum cv. Progress No. 9.

The metabolism of GA29 during seed maturation in Pisum sativum cv. Progress No. 9 was further investigated. [17-(13)C1]GA29 was metabolised to a GA-catabolite (structure 3), with incorporation of the [(13)C] label from the GA29 substrate into the GA-catabolite being demonstrated by GC-MS. Quantitation of the GA-catabolite using GC-MS was achieved by adding GA-catabolite, labelled with [(18)O], to seed extracts as an internal standard. At least 50% conversion of [(13)C1]GA29 to [(13)C1]GA-catabolite was demonstrated with the build up of exogenous [(13)C1]GA-catabolite strictly paralleling the accumulation of native GA-catabolite. These results strongly suggest that conversion of GA29 to the GA-catabolite is a natural metabolic step occurring during the final stages of seed maturation. 25 μg per seed of native GA-catabolite was recorded in 37 day old seeds. Some problems encountered in the analysis of extracts containing the GA-catabolite are discussed briefly.