The Induction of Glyoxysomal Enzyme Activities in the Aleurone Cells of Germinating Wheat

Abstract

The aleurone cells of quiescent Triticum vulgare grain were observed to contain glyoxysomes, but enzymes known to be located in this organelle were not detected. During germination the number of glyoxysomes increased, and their associated enzyme activities appeared, increasing up to the fifth or sixth day. The appearance of β-oxidation, isocitratase, and malate synthetase activities were largely dependent upon the presence of the embryo. Gibberellic acid (GA₂) was effective in replacing the embryo in this role. It is proposed, therefore, that the development of glyoxysomal enzyme activities and probably of the glyoxysomes themselves, is a gibberellic acid-dependent process. The developments of citrate synthetase and malate dehydrogenase activities were only partly dependent upon gibberellic acid. Since it is known that these enzymes are located in other compartments besides the glyoxysomes, it is proposed that their gibberellic acid-dependent activities are located in glyoxysomes while their gibberellic acidindependent activities are located in the cytosol and/or the mitochondria. The developmental courses of the gibberellic acid-independent activities and the results of studies using inhibitors of protein synthesis support this hypothesis