Studies on the Development and Localization of Catalase and H2O2-generating Oxidases in the Endosperm of Germinating Castor Beans

During germination of castor bean seeds (Ricinus communis var. Hale), the changes of activity of catalase, uricase, and alpha-hydroxyacid oxidase of the endosperm follow a rise and fall pattern with a peak between day 4 and 5 similar to that observed for the glyoxylate cycle enzymes. After 3 days of germination, most of the activities of these enzymes are recovered from the glyoxysomal fraction separated by isopycnic sucrose density gradient centrifugation.The activities of the oxidases of the glyoxysomal fractions increase somewhat more slowly than those of catalase or isocitrate lyase during the first 3 days of germination. But separation of the oxidative enzyme activities from glyoxysomal isocitrate lyase activity was not achieved by density gradient centrifugation or by density gradient electrophoresis. The sedimentation velocities of these two kinds of enzyme activities were found to be identical. The role and regulation of the glyoxysomal uricase, glycolate oxidase, lactate oxidase, and catalase activity in endosperm cells are discussed.