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Effect of Gibberellin A₃ on the Endoplasmic Reticulum and on the Formation of Glyoxysomes in the Endosperm of Germinating Castor Bean ¹

Department of Biology, University of California, Los Angeles, California 90024

Seedlings of castor bean (Ricinus communis cv. Hale) were exposed to a range of concentrations of gibberellin A₃ (GA₃). Treatments for 20 hours with GA₃ concentrations of 0.5 µM or higher resulted in increased levels of NADH-cytochrome c reductase, phosphorylcholine glyceride transferase, and malate synthase in endoplasmic reticulum (ER) isolated from endosperm on linear sucrose gradients. GA₃ treatment also resulted in increased RNA associated with ER. Malate synthase and catalase in crude homogenates were enhanced by 1 to 100 µM GA₃ concentrations. Isocitrate lyase, citrate synthase, malate synthase, catalase, and glycolate oxidase in isolated glyoxysomes were enhanced by 60, 20, 18, 40, and 28%, respectively, over controls. Treatment with abscisic acid led to decreased levels of glyoxysomal enzymes and reduced glyoxysomal protein. The effect of GA₃ and abscisic acid on the specific activities of glyoxysomes of different densities suggests that GA₃ influences enzyme levels and glyoxysome assembly.