Waterlogging and simulated acid rain after anthesis deteriorate starch quality in wheat grain

The synthesis and accumulation of starch is greatly affected by environmental stress. Wheat grown in the downstream area of the Yangtze River is easily subjected to stress of waterlogging and acid rain. In order to probe the effect of waterlogging and acid rain on yield and starch characteristic, we used winter wheat cultivars of Yangmai 16 (more resistant) and Wennong 17 (relatively sensitive) to sole stress of acid rain or waterlogging and to their combinations during grain filling. The responses of grain yield, the physiochemical properties and morphology of starch granules in endosperm to the stresses were investigated. Compared with CT (control), grain yield in Wennong 17 were significantly decreased by both pH 4.0 acid rain and pH 2.5 acid rain, while in Yangmai 16 only by pH 2.5 acid rain. Waterlogging combined with acid rain significantly reduced grain weight and grain yield in both wheat cultivars. Acid rain, waterlogging and their combination depressed activities of ADP glucose pyrophosphorylase and soluble starch synthase (SSS) in grains of both cultivars. Acid rain and waterlogging damaged endosperm cell structure and caused abnormal starch granules. Starch granules at maturity became fragile and failed to keep in shape and some granules were even totally submerged in the protein matrix and other tissue under acid rain and waterlogging. Content of amylopectin and amylopectin/amylose ratio was also decreased, while content of amylose was increased under acid rain and waterlogging. As a result, swelling power and most viscosity parameters decreased, while the pasting temperature increased in both cultivars due to stresses. In sum, acid rain and waterlogging and their combination damaged cell structure and depressed synthesis of amylopectin, and led to the formation of abnormal fragile starch granules, and finally reduced grain weight and then yield, and deteriorated starch quality.