Starch Granule Size Distribution in Wheat Grains under Irrigated and Rainfed Conditions

Abstract

Starch granules comprise 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 genotype and environment factors. Currently little information is available about the different distribution of starch granule size in wheat under different cul-tivation conditions. We used two wheat cultivars, Lumai 21 (starch content 68.9%) and De 99-3 (starch content 64.6%), to inves-tigate the distribution of grain starch granule size under irrigated and rainfed conditions at Tai’an and Dezhou of Shandong Prov-ince in 2004–2005 growth season. The irrigated treatment received 3 irrigations with the total water amount of 2 250 m2 ha?1 dur-ing the whole growth period (750 m3 ha-1 each at before sowing, pre-wintering, and jointing stages, respectively), while the rain-fed treatment had no irrigation. In mature grains, the diameter of starch granules ranged from 0.37 to 52.60 μm, and the percent volume distribution showed a 2-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. A 2-peak curve was also shown in percent surface area distribution of starch granules, but only one peak in percent number, because the number of B-type granules ac-counted for over 99% of the total starch granules. As compared with irrigated treatment, rainfed treatment affected the distribution of starch granules in grains of both cultivars through increasing the percent volume and percent surface area of 2.0?9.8 μm and 9.8 μm starch granules and decreasing those of 18.8 μm starch granules. The soil water deficit also decreased the contents of amylose and starch in grains and increased protein content, peak viscosity and final viscosity, suggesting that rianfed treatmentmay improve wheat grain quality. The contents of amylose, starch, and protein in grains were significantly correlated with the percent volume of starch granules with different diameter ranges. For starch, the r was -0.560*, -0.831** (2.0-9.8 μm) and -0.597*, -0.812** (9.8 μm); and for protein, the r was 0.799**, 0.603*, (2.0-9.8 μm) and 0.799**, 0.578* (9.8 μm), respectively. The result suggested that small starch granules (2.0-9.8 μm 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 μm and 9.8 μm) high in contents of amylose and starch.