CHARACTERIZATION OF THE ENDOPROTEASES APPEARING DURING WHEAT-GRAIN DEVELOPMENT

The pattern of endoproteolytic activities occurring during wheat (Trit icum aestivum, cultivar Chinese Spring) grain development was investig ated. Total endoprotease activity, assayed in solution with azocasein as a substrate, increased during the early stages of grain development to reach a maximum at 15 d postanthesis that was maintained until the grain was mature. Endoprotease activity was also assayed in gradient polyacrylamide gels co-polymerized with gelatin. The increase in endop roteolytic activity was due to the appearance of up to 18 endoproteoly tic bands that were arbitrarily classified into five groups (A, B, C, D, and E). The presence of serine, aspartic, metallo, and, to a lesser extent, thiol proteases in developing wheat grains was demonstrated b y the use of class-specific protease inhibitors. The appearance of the different classes of endoproteases during seed development was subjec t to temporal control; serine proteases were more abundant at early st ages and aspartic and metallo proteases were more abundant at later st ages. At intermediate stages of development (15-20 d postanthesis), mo st of the endoproteases were localized in the aleurone, testa, and emb ryo. The content of acidic thiol proteases was low in the developing s tarchy endosperm.