Wheat genome specific granule-bound starch synthase I differentially influence grain starch synthesis.

Wheat grain development is a complex process and is characterized by changes in physicochemical and structural properties of starch. The present study deals with endosperm starch physicochemical properties and structure during development in different granule-bound starch synthase I (GBSSI) null also known as waxy (Wx) genotypes. The study was conducted with pure starch isolated from wheat grains at 3-30 days post anthesis (DPA), at 3-day intervals. Amylose concentration increased throughout grain development in non-waxy (7.2-30.5%) and partial waxy genotypes (6.0-26.8%). Completely waxy genotype showed 7.0% amylose at 3 and 6 DPA, which declined during development and reached non-detectable quantities by 30 DPA. Amylopectin structure had a higher content of short chains at 3 DPA, which decreased continuously until 12 DPA, after which there were only minor changes in amylopectin chain length distribution. Similarly, the average degree of polymerization (DP) increased from 3 DPA (12.3) to 12 DPA (15.0), and then did not differ significantly up to 30 DPA (15.0). This suggests the formation of basic amylopectin architecture in wheat by 12 DPA. Wx-B and Wx-D affected amylopectin short chains mostly of DP 6-8 at 3 and 6 DPA. Wx-A affected the same fraction of chains at 9 and 12 DPA, and Wx-D affected DP 18-25 chains from 18 to 30 DPA, suggesting differential effect of waxy isoproteins on amylopectin structure formation.
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