Distribution of Starch Granule Size in Grains of Wheat Grown Under Irrigated and Rainfed Conditions

Abstract

Starch granule comprises A and B types in mature wheat ( Triticum aestivum L.) grains, which are different in chemical composition and functional properties. The granule size distribution of wheat starch is affected by both genotypic and environmental factors. Two wheat cultivars, Lumai 21 (starch content 68.9%) and De 99-3 (starch content 64.6%) were used to investigate the distribution of grain starch granule size, under irrigated and rainfed conditions, at Tai'an and Dezhou in Shandong Province, in the 2004–2005 growing season. In mature grains, the diameter of starch granules ranged from 0.37 to 52.60 μm, and the percent volume distribution showed a two-peak curve with the mean granule diameter of 5 (B type) and 25 μm (A type) at each peak. The volume percentages of A and B types were 56.1–65.5% and 34.5–43.9%, respectively. The two-peak curve was also shown in the percent surface area distribution of starch granules, but only 1 peak was seen in the percent number, because the number of B-type granules accounted for over 99% of the total starch granules. Compared with the irrigated treatment, the rainfed treatment affected the distribution of starch granules in grains of both cultivars by increasing the percent volume and the percent surface area of 2.0–9.8 and <9.8 μm starch granules, and decreasing those of >18.8 μm starch granules. Soil water deficit also decreased the contents of amylose and starch in grains, but increased protein content, peak viscosity, and final viscosity. This indicated that the rainfed treatment probably improved the wheat grain quality. In the 2 cultivars, the contents of amylose and starch in grains had significantly negative correlations to the percent volume of 2.0–9.8 and <9.8 μm starch granules, whereas, the content of protein in grains was significantly positively correlated with the percent volume of the 2 types of starch granules. This suggests that small starch granules (2.0–9.8 and <9.8 μm) are low in contents of amylose and starch, and high in protein content, whereas, big starch granules (9.8–18.8 and >9.8 μm) are high in both the contents of amylose and starch.