Metabolism of [ 3H]gibberellin A 5 in developing pharbitis nil seeds

Abstract

The native gibberellin A 5 (GA 5), as [1- 3H]GA 5 (3.2 Ci/mmol) was fed to seed capsules (0.58 μCi/capsule) of Pharbitis nil cv Violet at the 2-week stage of development, and its metabolism in the seeds was investigated after 43 hr. Extractable radioactivity in free GA metabolites was 38%, with 56% in GA glucosyl conjugate-like substances. Only 2.5% of the extractable radioactivity remained as [ 3H]GA 5. Tentative identifications, based on comparisons with authentic standards after sequential chromatography on silica gel partition column → gradient-eluted C 18 HPLC → isocratic-eluted C 18 HPLC-radiocounting (RC), showed that [ 3H]GA 5 was converted to at least six free GAs, GA 1, GA 3, GA 6, GA 8, GA 22, GA 29, a GA 5 methyl ester-like metabolite, and at least twelve GA glucosyl conjugate-like substances, GA 5-glucoside (GA 5-G), GA 5-glucosyl ester (GA 5-GE), GA 1-O(3)-G, GA 1-O(13)-G, GA 1-GE, GA 3-O(3)-G, GA 3-O(13)-G, GA 3-GE, GA 6-G or GE, GA 8-O(2)-G, GA 22-G or GE and GA 29-O(2)-G. After lower specific activity feeds of [1,2- 3H]GA 5 (74 mCi/mmol; 0.1 μCi/capsule) at approximately the same stage of development, the presence of GA 1, GA 3, GA 5, GA 6, GA 8 and GA 29 was further confirmed by sequential (after C 18 HPLC-RC) capillary gas chromatography-selected ion monitoring (GC-SIM), using six characteristic ions. However, for GA 22 only a trace of the parent ion was present at the appropriate retention time.