Effects of Inhibition of Starch Branching Enzyme on in situ Degradation of Endosperm Starch During Rice Seedling Growth

Cereal endosperm with inhibition of starch branching enzyme (SBE) increases resistant starch content and has health benefit. For plants, endosperm starch is degraded to provide energy for seedling growth. However, whether the inhibition of SBE influences in situ degradation of starch during seedling growth is seldom reported. In this study, a normal japonica rice cultivar Wu-xiang 9915 (WX) and its derived transgenic rice line (WTR) with inhibition of SBE were cultivated in the dark only in deionized H2O. The plant growth and starch property changes were investigated during seedling development. Compared with WX, WTR showed a significantly slow plant growth. The slow degradation of starch in seed restrained the plant growth. For WX, the amylopectin and amylose were simultaneously degraded, leading to that the endosperm residual starches had similar crystalline and short-range ordered structure during seedling development. However, for WTR, the amylopectin had higher resistance to in situ degradation than amylose, and endosperm residual starches changed from CA- to CB-type and its ordered structure increased during seedling development.