| The study was conducted on the Experimental Farm of Jiangsu Provincial Key Lab of Crop Genetics and Physiology of Yangzhou University, from 2007 to 2009. The study included two experiments, a field experiment and a pot experiment. The field experiment was carried out to investigate the effects of nitrogen on grain starch structure and physicochemical parameters in six non-waxy wheat varieties and two waxy wheat varieties which are widely planted. The pot experiment was also conducted in an artificial intelligent greenhouse to explore the effects of temperature during grain filling stage on grain starch structure and physicochemical parameters. It is hopeful to expand the understanding of starch synthesis mechanism and provide theoretical reference for producing wheat with good grain quality. The main results were as follows.1. The starch structure and physicochemical properties of different genotypes of wheatCompared with medium-gluten, weak-gluten, and waxy genotypes, the percentage of the volume and external area of Type B and C granules in high-gluten wheat Qinmai 11 were lower, the percentage of Type A granules was higher, and the percentage of the number of Type C granules was the lowest. Of all the genotypes, the percentages of the external area and the number of Type C granule were the highest in medium-gluten wheat Yangmai 16. Of all the genotypes, weak-gluten wheat Ningmai 9 had the lowest percentages of the volume and external area of Type A and the highest percentage of Type B granules. The volume percentage of Type C granule in Waxy genotype was higher as compared with non-waxy genotype. The percentage of long B-chain followed a descending order of Yangmai 15, Yangmai 16, Ningmai 9, and Qinmai11. The percentage of intermediate B-chain followed a descending order of Qinmai11, Yangmai 16, Ningmai 9, WX-13, and Yangmai 15. The order of the percentages of short B-chain and A-chain was WX-13﹥Ningmai 9﹥Yangmai 15﹥Yangmai 16﹥Qinmai 11. The order of damaged starch content and swelling power of different genotypes was high-gluten﹥medium-gluten﹥weak-gluten. Peak viscosity, trough viscosity, and final viscosity followed a descending order of medium-gluten, weak-gluten, and high-gluten. The order of enthalpy of gelatinization was Ningmai 9﹥Qinmai11﹥Yangmai 16. The order of retrogradation was Qinmai11﹥Yangmai 16﹥Ningmai 9.2. Effects of nitrogen on grain starch structure and physicochemical parametersThe percentages of volume and external area of Type B and C starch granules were increased as the increased applied N amount. The percentages of volume and external area of Type A starch granules, however, were decreased as the increased applied N amount. The percentage of the number of Type C granule increased as the increased applied N amount. As the increase of applied N amount, the percentages of long B-chain and intermediate B-chain declined, the percentages of short B-chain and A-chain percentage increased. Compared with non-nitrogen treatment, the swelling power and solubility of wheat grain starch were much higher. The enthalpy of gelatinization of starch was the lowest when the applied N amount was 180kg/ha. The starch retrogradation was declined as the increased N application amount.3. Effects of high temperature on grain starch structure and physicochemical parametersAs the high temperature stress progressed, the percentages of the volume and external area of Type C starch granules declined and the percentages of the volume and external area of Type B increased. The percentage of the number of Type C starch granules was increased during the early and middle stages of grain filling. The stress of high temperature promoted the development of long B-chain, especially during 20– 22 d after anthesis. The content of damaged starch, swelling power, solubility, viscosity, and thermal properties were highly vulnerable to high temperature stress during 20– 22 d after anthesis..4. The relationship between grain starch structure and physicochemical characteristicsThe content of amylose and amylopectin, the ratio of amylose content to amylopectin content, and long B-chain were positively correlated to peak viscosity, trough viscosity, final viscosity at the 0.01 or 0.05 probability level. These parameters were negatively correlated to swelling power, also at the 0.01 or 0.05 probability level. The percentages of short B-chain and A-chain were negatively correlated to the content damaged starch at 0.01 or 0.05 probability level, and positively correlated to enthalpy of gelatinization at less than significant level.
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