PATTERN OF ENDOPROTEOLYSIS FOLLOWING WHEAT-GRAIN GERMINATION

Following cereal grain germination the starch and storage proteins acc umulated in the starchy endosperm are mobilized by the concerted actio n of hydrolytic enzymes, such as amylases and proteases, that are prod uced and secreted by the scutellum and the aleurone layer. We have stu died the pattern of endoproteolytic activities following wheat (Tritic um aestivum cv. Chinese Spring) grain germination using SDS-PAGE conta ining a gradient of polyacrylamide copolymerized with gelatin, an arti ficial substrate for plant proteases. Total proteolytic activity incre ased as seedling growth proceeded and reached a maximum 5-7 days after imbibition. Up to 20 proteolytic bands could be detected in extracts from these grains. The bands were arbitrarily classified into 3 groups ; endoproteases of groups I and II showed higher activity at pH 6.5, w hile those of group III had maximum activity at pH 4.0. Most of group II and III endoproteases were produced by the aleurone layer and scute llum and secreted to the starchy endosperm. The synthesis of most of t he proteases of group III, but not of group II, was activated by exoge nous GA(3) in de-embryonated wheat grains. Based on activation by thio l-reagents and inhibition by thiol-protease inhibitors, it was determi ned that GA(3)-induced proteases were thiol-proteases.