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Influence of starch synthase III on the cluster structure of maize starch
F. ZHU (1), E. Bertoft (2), K. Seetharaman (2). (1) University of Auckland, Auckland, New Zealand; (2) University of Minnesota, St. Paul, MN, U.S.A.

Molecular structure of starches from <i>dull1</i> maize mutants deficient in starch synthase III (SSIII) with a common genetic background (W64A) were compared with the wild type. Amylose content was higher and the structure was altered as revealed by gel-permeation chromatography. Super-long chains of amylopectin were found in all non-waxy samples. Unit chain length distribution and internal chain length distribution (of amylopectins and their φ,β-limit dextrins, respectively) was analyzed by anion-exchange chromatography after debranching. Deficiency of SSIII led to increased amount of shorter chains in both amylopectin and φ,β-limit dextrins, suggesting a difference in their cluster structure.

Clusters were subsequently produced from the amylopectins by partial hydrolysis with α-amylase of <i>Bacillus amyloliquefaciens.</i> The composition of chains and building blocks (α-limit dextrins) in the clusters were then analyzed and showed that the <i>dull1</i> mutation resulted in larger clusters with ~5.4 building blocks compared to ~4.2 blocks in the wild type. The major reason was an increase of the small, singly branched building blocks. The results from <i>dull1</i> maize mutants were compared with a similar SSIII-deficient mutation in barley (<i>amo1</i>) and a fundamental difference in their building block composition of the clusters was observed.

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