The relationship between starch synthesis enzyme activity, gene expression, and amylopectin fine structure in waxy maize

Two waxy maize hybrids were selected to explore the relationship between amylopectin fine structure and gene expression of starch synthesis-related enzymes. High-performance anion-exchange chromatograph analysis showed that waxy maize had the highest content of amylopectin B1 chain (DP 13-24) and the secondary proportion of A chain (DP 6-12) while the low proportions of B2 (DP 25-36) and B3 chains (DP >= 37). SBE activity was positively correlated with the proportion of A chain and negatively correlated with the proportion of B3 chain and average chain length, but DBE activity showed the almost opposite relation. AGPase and SSS activities were not found to be significant with chain-length distribution. SSI preferentially generated short A chain, which would be elongated further by SSIIa to produce long B1 chain that was continued to extend by SSIIIa to produce longer B2 and B3 chains. SBEI was more likely responsible for the synthesis of B2 and B3 chains, while SBEIIb played a specific role in the formation of A chain. ISA2 regulated amylopectin structure through the removal of A and B1 chains and the formation of B2 and B3 chains.