Relationship among the key enzymatic activities involved in starch synthesis and amylopectin chain distributions in developing wheat grain

Abstract

The aim of this study was to investigate the relationship among the activities of the key enzymes involved in starch synthesis and the fine structure of amylopectin in non-waxy and waxy types of wheat. Amylose, amylopectin, and starch accumulation increased continuously after anthesis and increased as a sigmoid curve during the grain filling stage. The accumulation rates showed single-peak curves and all reached their peaks at 20 days after anthesis (DAA). Adenosine diphosphate glucose pyrophosphorylase (AGPP), soluble starch synthase (SSS), granule-bound starch synthase (GBSS), and starch-branching enzyme (SBE) activities each showed a single-peak curve during grain filling and peaked at 20 to 25 DAA. A significantly positive or positive correlation was observed between the amylose, amylopectin, and starch accumulation rates and the activities of the aforementioned enzymes. Different amylopectin chain contents changed continually during grain development and varied differently between the two types of wheat. Moreover, the AGPP, SSS, GBSS, and SBE activities exhibited a close correlation with the different chains of amylopectin. The result shows that starch biosynthesis depends on the coordinated effects of the said enzymes. The SSS activity was earlier detected and had an activity level higher than that of GBSS at the early grain filling stage. Moreover, amylose was not found at 5 DAA, while amylopectin had already appeared. Based on the results, amylopectin synthesis is suggested to precede amylose synthesis. Key words: Common wheat (Triticum aestivum L.), Key enzyme, Starch synthesis, Amylopectin structure.