Change in Grain Protein Composition of Winter Wheat Cultivars Under Different Levels of N and Water Stress

Abstract

Hard white winter (HWW) wheat cultivars in the U.S. must have superior protein quality and consistent processing quality to be successful in the Asian market. Dough rheological properties, baking quality, and end-product attributes are significantly affected by grain protein content and composition. Protein composition, in terms of size and solubility, has been found to be determined by both genetics and environmental conditions. This study investigated the combined influences and interactions of moisture deficit and N management on rheological properties, protein quality, and protein molecular weight distributions of HWW grown in Oregon. Grain was obtained from seven HWW wheat cultivars and two soft white winter (SWW) wheat cultivars grown under line-source irrigation systems in 2002 and 2003. Trials were managed to provide three levels of moisture (100, 80, and 50 % of optimum) over plots receiving two levels of soil nitrogen. The selected cultivars were highly variable for glutenin composition. Protein composition was characterized using size-exclusion HPLC. Resulting chromatograms were divided into three components, which corresponded to HMW and LMW glutenins, gliadins, and non-gluten forming albumins and globulins. Mixograph analyses and SDS sedimentation tests were used to measure variation in protein quality and dough rheological properties. Significant variation in quality was observed among cultivars, irrigation levels, and fertilization rates. Hard wheat cultivars had significantly higher amounts of polymeric proteins (glutenins) than the soft wheat cultivars over both N and water treatments. Concentrations of polymeric proteins were increased under water stress as compared with well-watered conditions for both HWW and SWW cultivars. Moisture stress contributed to higher SDS sedimentation values, although mixing time and mixing tolerance were relatively less affected. As protein content increased, the relative proportion of gliadin proteins also increased, regardless if the protein increase was related to soil N or water stress. Albumin and globulin proteins were the least responsive to changes in protein content. Significant irrigation × N interactions were observed for protein composition and SDS sedimentation volume. AMMI analyses were further used to investigate interactions of water stress and N inputs on key flour quality attributes. Crop management strategies need to consider interactions between moisture stress and N fertilization to reach desired targets for flour quality and end-product performance