Effect of gibberellin a(3) on the endoplasmic reticulum and on the formation of glyoxysomes in the endosperm of germinating castor bean.

Seedlings of castor bean (Ricinus communis cv. Hale) were exposed to a range of concentrations of gibberellin A(3) (GA(3)). Treatments for 20 hours with GA(3) concentrations of 0.5 muM 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. GA(3) treatment also resulted in increased RNA associated with ER. Malate synthase and catalase in crude homogenates were enhanced by 1 to 100 muM GA(3) 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 GA(3) and abscisic acid on the specific activities of glyoxysomes of different densities suggests that GA(3) influences enzyme levels and glyoxysome assembly.