On the Development of the Ribosomal System in the Endosperm of Germinating Castor Bean Seeds

The important work of Beevers and collaborators on the metabolic evolution of the castor bean endosperm demonstrates the fitness of this material for the study of the biochemical activation during the early phase of seed germination. As shown by these authors. both respiration in vivo and the oxidative activity of mitochondrial preparations markedly increase during the first 2 to 3 days of germination (1, 4). Parallel qualitative changes of the enzymatic pattern are revealed by the appearance and the rapid rise of the activity of malate synthetase and isocitritase. 2 enzymes involved in the conversion of lipids into carbohydrates (7, 24). The finding of an increase of the protein nitrogen in the mitochondrial fraction (1) provided a first suggestion that the observed rises of enzyme activities could be related to de novo enzyme synthesis. A series of investigations in this laboratory confirmed and extended the above observations. The increase of enzvme activities in the endosperm of the germinating castor bean seed was found to be a general phenomenon, involving all of the glycolytic enzymes investigated, glucose-6-P and 6-P-gluconate dehydrogenases (11), ornithine transcarbamylase, ascorbate oxidase (Forti G. and M. Ranalletti. personal comn'unication), ribonuclease (24), and in the mitochon(dria, malate dehydrogenase, succinate-cytochrome c reductase and cytochrome oxidase (3). Studies on the development in vivo of mitochondrial enzymes, and on reactivation in vitro of some glycolytic enzymes indicated that some of the enzyme activities inicrease in the very early period of germination is due to the transition from the inactive to the