GIBBERELLIN-PHOTOAFFINITY LABELING OF WILD OAT (AVENA-FATUA L) ALEURONE PROTOPLASTS

Aleurone protoplasts of wild oat (Avena fatua L.), and subcellular fra ctions isolated from them, were photoaffinity labeled using the synthe tic gibberellin (GA) derivative thia)propan-3'-ol-4-azido-5-[I-125]iod osalicylate. Labeled polypeptides were identified by electrophoresis u nder denaturing conditions followed by autoradiagraphy. GA-photoaffini ty labeling of both intact protoplasts and isolated subcellular fracti ons led to the covalent attachment of the reagent to many polypeptides . A 50 kD polypeptide in the soluble fraction of homogenates of aleuro ne protoplasts GA-photoaffinity labeled in vivo showed specific bindin g. The biologically active GA(1), GA(4) and 4)-17-yl-1'(1'-thia)propan -3'-ol-4-azidosalicylate completed for binding whereas the biologicall y inactive GA(8) and GA(34) did not. The GA-photoaffinity labeling cha racteristics of this polypeptide suggested that:it might interact spec ifically with biologically active GAs in vivo. Attempts to detect spec ific GA-binding in in vitro GA-photoaffinity labeling experiments met with only limited success perhaps indicating the labile nature of spec ific binding observed in vivo. The potential of GA-photoaffinity label ing for identifying GA-binding proteins in aleurone and other GA-respo nsive tissues is discussed.