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Intracellular Localization of Peptide Hydrolases in Wheat (Triticum aestivum L.) Leaves ¹

Plant Sciences Section, School of Agriculture and Forestry, University of Melbourne, Parkville, Victoria 3052, Australia

Protoplasts from 8- to 9-day-old wheat (Triticum aestivum L.) leaves were used to isolate organelles which were examined for their contents of peptide hydrolase enzymes and, in the case of vacuoles, other acid hydrolases. High yields of intact chloroplasts were obtained using both equilibrium density gradient centrifugation and velocity sedimentation centrifugation on sucrose-sorbitol gradients. Aminopeptidase activity was found to be distributed, in approximately equal proportions, between the chloroplasts and cytoplasm. Leucyltyrosine dipeptidase was mainly found in the cytoplasm, although about 27% was associated with the chloroplasts. Vacuoles shown to be free from Cellulysin contamination contained all of the protoplast carboxypeptidase and hemoglobin-degrading activities. The acid hydrolases, phosphodiesterase, acid phosphatase, -mannosidase, and -N-acetylglucosamidase were found in the vacuole to varying degrees, but no -glucosidase was localized in the vacuole.