Amylases synthesis in scutellum and aleurone layer of maize seeds

The endosperm of germinating maize seeds contains four isozymes of alpha-amylases (alpha-amylase-1 to -4) and one isozyme of beta-amylase. The alpha-amylases were purified by affinity chromatography on amylose and separated by DEAE-cellulose chromatography, into two groups, namely alpha-amylases-1,2 and alpha-amylases-3,4; and beta-amylase was purified by precipitation as a glycogen-enzyme complex. The molecular weight of alpha-amylases-1 and -2 was 46 kD, alpha-amylases-3 was 44.5 kD and of alpha-amylases-4 was 47.5 kD. The molecular weight of beta-amylase was 56 kD. During seed germination increase in amylolytic activity in endosperm was mainly contributed by secretion of alpha-amylases from adjoining aleurone layer and scutellum. The synthesis and secretion of alpha-amylases was first initiated in the scutellum followed by aleurone layers. Exogeneous Ca2+ stimulated synthesis of alpha-amylases in both eleurone layer and scutellum. In contrast, though scutellum and aleurone layer synthesized beta-amylase but it was not secreted to the medium. These results suggest that during the early germination period, alpha-amylases secreted from scutellum mobilizes starch.