Heat stress in filling stage confers distinct effect on starch granules formation in different thermotolerant wheat accessions

Heat stress affects the accumulation of starch, which is responsible for the major loss in wheat (Triticum aestivum L.) yield. Clarifying the changes of starch composition and granule particles in wheat grain under heat stress are required for understanding the heat adaptation of wheat. The investigation of starch granule morphology and the amylose/amylopectin ratio in seven spring wheat lines of varying levels of thermotolerance under heat stress revealed that A-type starch granules generally decreased and medium granules (between A-type and B-type granules) dramatically increased in the heat-sensitive wheat lines after heat stress compared with the heat-resistant lines. A remarkable decrease in amylopectin was also observed in the heat-sensitive wheat lines. Alterations in A-type starch granules and amylopectin deposition were found to be responsible for the reduction in grain width and weight following heat stress in the heat-sensitive wheat lines. These results provide new insights into the heat effect on wheat starch formation.