LAUSR

Abstract Up to now, no information on the structural characteristics of glucans involved in the initiation of starch biosynthesis in cereal endosperm has been available. Since amylopectin is a major constituent of starch and largely affects the starch physicochemical properties, we attempted to characterize the fine structures of branched glucans. We isolated small glucan granules with a diameter of approximately 40–80 nm from rice endosperm at the early developmental stages and analyzed the chain-length distribution of the glucans and their phosphorylase-limit dextrins. Compared with normal amylopectin, the proportion of long chains of these glucans with degree of polymerization (DP) ≥ 35 was significantly lower and these long chains did not form a peak. These structural features were commonly found in small glucan granules in three rice cultivars. Based on the present results, we propose that these immature glucans located in small granules in young endosperm are involved in the initiation process of amylopectin biosynthesis in rice endosperm.