Contents and structures of branched and linear maltodextrins, malto-oligosaccharides, and sugars in the early developmental stage of phosphorylase1 mutant endosperm of rice

Biochemical analysis of plastidial phosphorylase (Pho1)-deficient mutants of rice strongly suggests that Pho1 plays an important role in the initiation of starch biosynthesis in the endosperm. The present study examined structures and amounts of maltodextrins, malto-oligosaccharides (MOS) as well as sugars in maturing rice endosperm and compared between a pho1-mutant line EM633 and its wild-type cultivar Taichung-65 (TC65). By using a gel permeation HPLC from developing rice endosperm of both lines, branched maltodextrins (BMD) with distinct fine structure could be isolated for the first time, a possible intermediate in the initiation process of starch biosynthesis, whereas its amount was much lower than starch content in both endosperms. This suggests that BMD as a main intermediate in the de novo synthesis of starch molecules is kept to be at a very low level during starch biosynthesis. The amounts of maltose, and MOS as well as linear maltodextrins (LMD) were greatly increased by the pho1 mutation. These results indicate that Pho1 would play an essential role in the step of mobility of maltose to MOS and then to LMD in the de novo synthesis of amylopectin molecules in developing rice endosperm.