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Development and Growth Regulation

Developmental Regulation of the (1,3)--Glucan (Callose) Synthase from Tomato ¹

Possible Role of Endogenous Phospholipases

Department of Food Science, New Jersey Agricultural Experiment Station, Cook College, Rutgers University, New Brunswick, New Jersey 08903-0231, U.S. Department of Agriculture, Agricultural Research Service, Horticultural Crops Quality Laboratory, Building 002, Beltsville, Maryland 20705

Activity levels of UDP-glucose: (1,3)--glucan (callose) synthase in microsomal membranes of pericarp tissue from tomato fruit (Lycoperisicon esculentum Mill, cv Rutgers) were determined during development and ripening. Addition of the phospholipase inhibitors O-phosphorylcholine and glycerol-1-phosphate to homogenization buffers was necessary to preserve enzyme activity during homogenization and membrane isolation. Enzyme activity declined 90% from the immature green to the red ripe stage. The polypeptide composition of the membranes did not change significantly during ripening. The enzyme from immature fruit was inactivated by exogenously added phospholipases A₂, C, and D. These results suggest that the decline in callose synthase activity during ontogeny may be a secondary effect of endogenous lipase action.