Abstract
Metabolism of [(14)C]gibberellin (GA) A(12) (GA(12)) and [(14)C]gibberellin A(12)-aldehyde (GA(12)-aldehyde) was examined in cotyledons and seed coats from developing seeds of pea (Pisum sativum L.). Both were metabolized to only 13-hydroxylated GAs in cotyledons but to 13-hydroxylated and non-13-hydroxylated GAs in seed coats. The metabolism of [(14)C]GA(12) was slower in seed coats than in cotyledons. [(14)C]GA(12)-aldehyde was also metabolized to conjugates in seed coats. Seed coat [(14)C]-metabolites produced from [(14)C]GA(12)-aldehyde were isolated by high-performance liquid chromatography (HPLC). Conjugates were base hydrolyzed and the free GAs reisolated by HPLC and identified by gas chromatography-mass spectrometry. [(14)C]GA(53)-aldehyde, [(14)C]GA(12)-aldehyde conjugate, and [(14)C]GA(53)-aldehyde conjugate were major metabolites produced from [(14)C]GA(12)-aldehyde by seed coats aged 20-22 days or older. The dilution of (14)C in these compounds by (12)C, as compared to the supplied [(14)C]GA(12)-aldehyde, indicated that they are endogenous. Feeding [(14)C]GA(53)-aldehyde led to the production of [(14)C]GA(53)-aldehyde conjugate in seed coats and shoots and also to 13-hydroxylated GAs in shoots. Labeled GAs, recovered from plant tissue incubated with either [(14)C]GA(12), [(14)C]GA(12)-aldehyde, or [(3)H]GA(9), were used as appropriate markers for the recovery of endogenous GAs from seed coats or cotyledons. These GAs were purified by HPLC and identified and quantified by gas chromatography-mass spectrometry. GA(15), GA(24), GA(9), GA(51), GA(51)-catabolite, GA(20), GA(29), and GA(29)-catabolite were detected in seed coats, whereas GA(9), GA(53), GA(44), GA(19), GA(20), and GA(29) were found in cotyledons. The highest GA levels were for GA(20) and GA(29) in cotyledons (783 and 912 nanograms per gram fresh weight, respectively) and for GA(29) and GA(29)-catabolite in seed coats (1940 and > 1940 nanograms per gram fresh weight, respectively).