QUALITATIVE AND QUANTITATIVE-ANALYSIS OF ENDOGENOUS GIBBERELLINS IN ONION PLANTS AND THEIR EFFECTS ON BULB DEVELOPMENT

Evidence has been reported that bulb development in onion plants (Alli um cepa L.) is controlled by endogenous bulbing and anti-bulbing hormo nes, and that gibberellin (GA) is a candidate for anti-bulbing hormone (ABH). In this study, we identified a series of C-13-H GAs (GA12, GA1 5, GA24, GA9, GA4, GA34, and 3-epi-GA4) and a series of C-13-OH GAs (G A44, GA20, GA1, and GA8) from the leaf sheaths including the lower par t of leaf blades of onion plants (cv. Senshu-Chuko). These results sug gested that two independent GA biosynthetic pathways, the early-non-hy droxylation pathway to GA4 (active GA) and early-13-hydroxylation path way to GA, (active GA), exist in onion plants. It was also suggested t hat GA4 and GA1 have almost the same ability to inhibit bulb developme nt in onion plants induced by treatment with an inhibitor of GA biosyn thesis; uniconazole-P. The endogenous levels of GA, and GA4, and their direct precursors, GA20 and GA9, in leaf blades, leaf sheaths, and ro ots of 4-week-old bulbing and non-bulbing onion plants were measured b y gas chromatography/selected ion monitoring with the corresponding [H -2]labeled GAs as internal standards. In most cases, the GA levels in long-day (LD)-grown bulbing onion plants were higher than those of sho rt-day (SD)-grown non-bulbing onion plants, but the GA1 level in leaf blades of SD-grown onion plants was rather higher than that of LD-grow n onion plants. Relationship between the endogenous GAs and bulb devel opment in onion plants is discussed.