Relationship between Starch, Protein Accumulation and Substrate Supply during Grain Filling in Spring Wheat

Pot experiment was conducted to investigate the relationship between starch,protein accumulation and soluble sugar, total free amino acid contents during grain filling period with three wheat genotypes differing in both protein and yield. The results indicate that soluble sugar contents decreases dramatically from 5 to 20 days after anthesis, and starch content increases correspondingly. At later stage, there is slight rise or decline of starch content when soluble sugar content increases. As seeds develop, the total free amino acids decline gradually and the change of varietal protein content is consistent with free amino acids. The starch accumulation rate shows the pattern of parabola in all cultivars tested, and high yield and middle protein cultivar has the highest accumulation rate. It is proposed that the accumulation of starch is mainly dependent on ability of grain to utilize or syhthesize substrate and that of protein is more directly dependent upon restriction of source strength.