Induction of Glyconeogenic Enzymes by Gibberellin A3 in Endosperm of Castor Bean Seedlings

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Abstract
Seedlings of castor bean (R. communis cv. Hale) were exposed to GA3 (100 .mu.M) for periods up to 20 h. Endosperm homogenates were fractionated on linear sucrose gradients and enzymes in mitochondria, glyoxysome and cytosol fractions were assayed. GA treatment resulted in increases in the activities of enzymes in all 3 compartments. There were enzymes in all 3 compartments which were not affected by exogenous applications of GA3. The isozymes of L-aspartate-.alpha.-ketoglutarate aminotransferase in both mitochondria and glyoxysomes were induced coordinately; the isozymes of citrate synthase and malate dehydrogenase were not. All gluconeogenic enzymes in glyoxysomes are induced by GA3. With the exception of the mitochondrial malate dehydrogenase isozyme, all enzymes of the tricarboxylic acid cycle believed to participate in glyconeogenesis were increased. The cytosolic enzymes (malate dehydrogenase, phosphoenolpyruvate carboxykinase and fructose bisphosphatase) were induced, but the levels of pyruvate kinase and enolase were not affected by GA3 treatment.