Effects of drought stress and elevated CO₂ on starch fine structures and functional properties in indica rice

The changes in rice starch fine structures and functional properties induced by drought, elevated CO₂ (eCO₂) and combined treatments remain to be elucidated comprehensively. In this study, starch molecular structures were characterized by size-exclusion chromatography and fluorophore-assisted carbohydrate electrophoresis, and the data from amylopectin chain-length distributions was fitted with a mathematical model to obtain parameters for statistical analysis. Starch crystalline structures, thermal and pasting properties of rice flour were also analyzed. All the treatments decreased the seed setting rate and increased chalky grains, reflecting the abnormal starch accumulation. However, eCO₂ partially increased the seed setting rate and chalky grains under drought stress. The stress-treated starch samples had shorter amylopectin short and intermediate chains, the lower degree of ordered structures, but similar amylose content and relative crystallinity. This led to lower onset gelatinization temperature and paste viscosities, which may be responsible for the worse sensory quality of rice grains.