Constitution and Spatiotemporal Expression of Starch Branching Enzyme in Developing Wheat Grain

This study aimed at disclosing the enzymatic mechanism in amylopectin synthesis in wheat (Triticum aestivum L.).The isozyme forms, organ localization, spatiotemporal expression profile and subunits constitution of starch branching enzyme (SBE) were identified in eight wheat cultivars from different provenances using native polyacrylamide gel electrophoresis (Native-PAGE) and SDS-PAGE.Four SBE isozymes were detected in wheat endosperm, in which isozymes B and SBEIIa were localized in endosperm and leaf, whereas isozymes A and D i were exclusively present in endosperm.In the process of grain filling, D i and SBEIIa expressed first, followed by isozyme B, and isozyme A expressed finally.However, B and SBEIIa terminated to express at late filling stage.All SBE isozymes were composed of one subunit of 86-92 kD, and their spatial localization exhibited organ specificity.According to the expression level, D i , B, and SBEIIa are considered as dominant isozymes for grain endosperm development.They probably determinate the total SBE activity and serve as key factors in amylpectin biosynthesis in wheat grain and leaf.