<i>De Novo</i> Synthesis of Ribonuclease and β-1,3-Glucanase by Aleurone Cells of Barley

Abstract

When isolated aleurone layers of barley are incubated they produce a number of hydrolytic enzymes which can be divided into three groups. The synthesis and the secretion of the hydrolases in the first group is greatly enhanced by gibberellic acid. Using the density labeling technique of Filner and Varner (3) it has been shown that the increase in enzymatic activity of two of the enzymes in this group (a-amylase and protease) is due to de novo synthesis (3, 6). The marked effect of gibberellic acid on the rate of enzyme synthesis makes this an ideal system to study hormonal control of protein synthesis (10). The total enzymatic activity of hydrolases in the second group (e.g., ribonuclease and B-glucanase) does not show the same response to GA. There is a considerable increase in enzymatic activity during imbibition of the seeds, but the addition of GA to the isolated aleurone layers causes only a small increase in the total amount of enzyme activity (2, 7). However, release of these enzymes in the medium is dependent on GA, and this system has been used to study hormonal control of enzyme secretion (2, 7). Whether or not the increase in enzymatic activity which occurs during imbibition of the halfseeds and incubation of the aleurone layers is due to de novo synthesis has never been determined. Finally, the enzymatic activity of at least one hydrolase, /3-amylase, increases in the presence of GA, but this is due to release of preformed enzyme and not to de novo synthesis (5). We now present evidence consistent with the idea that two enzymes in the second group are also synthesized de novo.