Differential compartmentation of gibberellin a(1) and its metabolites in vacuoles of cowpea and barley leaves

Abstract

The metabolism and efflux of gibberellin A(1) (GA(1)) taken up by leaves of cowpea (Vigna sinensis cv. Blackeye pea No. 5), as well as the distribution of GA(1) metabolites in the protoplasts and vacuoles of cowpea and barley (Hordeum vulgare L. cv. Numar), were studied.GA(1) is metabolized rapidly in cowpea leaf discs to products tentatively identified as gibberellin A(8) (GA(8)) and gibberellin A(8) glucoside (GA(8)-glu). After labeling leaf discs with [(3)H]GA(1) for 1 hour, the release of radioactivity from the leaf was followed. Over a 12-hour period, the level of radioisotope in the tissue declined to about 35% of the original, after which no further release was observed. At this time, almost all of the radioactivity remaining in the leaf was GA(8)-glu, while most of the radioactivity which had been released was unmetabolized GA(1).Mesophyll protoplasts and vacuoles were isolated from cowpea and barley leaves previously fed [(3)H]GA(1). These protoplasts retain the ability to metabolize GA(1), indicating that neither the leaf structure nor the cell wall is necessary for this metabolism. A higher proportion of GA(8)-glu was found in the vacuoles relative to the entire protoplasts. The results obtained suggest that GA(1) metabolites are preferentially compartmentalized in the vacuoles relative to GA(1).