GIBBERELLIN BIOSYNTHETIC-PATHWAY AND THE PHYSIOLOGICALLY ACTIVE GIBBERELLIN IN THE SHOOT OF CUCUMIS-SATIVUS L

[H-2(2)]Gibberellin A24 (GA24) and [H-2(4)]-GA9 were applied to the apices of normal-type cucumber (Cucumis sativus L. cv. Yomaki) seedlings treated with uniconazole, an inhibitor of GA biosynthesis. The metabolites from these feeds were identified by full-scan gas chromatography-mass spectrometry (GC-MS) to confirm the conversions of [H-2(2)]GA24 to [H-2(2)]GA9 and of [H-2(4)]GA9 to [H-2(4)]GA4. The results show that GA4 is biosynthesized from GA24 via GA9. In a cucumber hypocotyl elongation bioassay using cv. Yomaki, prohexadione (DOCHC), an inhibitor of 2-oxoglutarate-dependent dioxygenase, inhibited the hypocotyl elongation caused by application of GA9, while DOCHC enhanced the elongation caused by application of GA4. These results indicate that GA4 is a physiologically active GA and that the activity of GA9 is due to its conversion to GA4 in cucumber shoots.