Differential Compartmentation of Gibberellin A1 and Its Metabolites in Vacuoles of Cowpea and Barley Leaves

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Abstract
The metabolism and efflux of GA1 taken up by leaves of cowpea, and the distribution GA1 metabolites in the protoplasts and vacuoles of cowpea and barley, were studied. GA1 is metabolized rapidly in cowpea leaf discs to products tentatively identified as GA8 and GA8 glucoside (GA8-glu). After labeling leaf discs with [3H]GA1 for 1 h, the release of radioactivity from the leaf was followed. Over a 12-h 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 GA8-glu, while most of the radioactivity which had been released was unmetabolized GA1. Mesophyll protoplasts and vacuoles were isolated from cowpea and barley leaves previously fed [3H]GA1. These protoplasts retain the ability to metabolize GA1, indicating that neither the leaf structure nor the cell wall is necessary for this metabolism. A higher proportion of GA8-glu was found in the vacuoles relative to the entire protoplasts. GA1 metabolites are apparently preferentially compartmentalized in the vacuoles relative to GA1.