Molecular structure of starch in grains is not affected by common dwarfing genes in rice (sd1) and sorghum (dw3)

Dwarf cereal crops are widely grown world‐wide because they offer productivity advantages to farmers, but the question of whether dwarfing genes change starch structure has not been examined. Starch properties, including digestion rate and mechanical properties of starch‐containing biomaterials, are influenced by its structure, and thus significant changes might have health implications. Starch molecular structures of the grains from a semi‐dwarf sd1 rice (Oryza sativa L.) mutant (Calrose 76) and its near‐isogenic wild‐type (Calrose) counterpart as well as of those from three dwarf sorghum (Sorghum bicolor L.) mutants and their near‐isogenic tall revertants (due to the spontaneous reverse mutation of dw3 gene) were analyzed to understand the pleiotropic effects of dwarfing genes on starch biosynthesis in the grains. The structures of (fully branched) whole starch molecules and branch‐chain length (from enzymatically debranched starch) were characterized using size‐exclusion chromatography. The weight–average MW and radius of gyration of whole starch molecules were characterized using multiple‐angle laser light scattering. There were no significant structural differences between each dwarf variety and its near‐isogenic wild‐type or tall revertant counterpart. Hence plant height reduction in rice and sorghum, controlled by the sd1 and dw3 genes, respectively, does not affect the biosynthesis of starch molecules in grains and is expected to have no significant impacts on starch crystalline and granular structures as well as starch functional properties, including its nutritional values.