Abstract
We have reported previously in 2002, a starch synthase I (SSI)-deficient mutant that has 1/6 SSI activity. In this study, we isolated new SSI mutant lines that had different SSI activity levels by PCR method from about 40,000 knockout rice population and analyzed the function of SSI. Four mutant lines have 1/4, 1/5, 1/6 and zero SSI activity compare to the wild-type. The proportion of α-polyglucans with DP of 8-12 in amylopectin was reduced in all lines. The degree of change in amylopectin structure was negatively correlated with the SSI activity. Leaf amylopectin in the null mutant also showed the same change. These results suggest that SSI plays a distinct role in the synthesis of α-1,4 polyglucans of DP8-12 in starch metabolism. Because the seed weight of the null mutant was unchanged, it appears that other SS isozymes complement the α-1,4 polyglucans synthesis in the endosperm.
