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Endosperm enrichment and physicochemical properties of superior and inferior grain starch in super hybrid rice.

Significant asynchronous phenomenon exists in super rice because of the different spikes and spikelet positions, which affect the accumulation and properties of starch. However, little is known about the endosperm enrichment and physicochemical properties of starch between superior and inferior grain in super hybrid rice. YY2640 was selected as the study material to investigate the enrichment and physicochemical properties of starch between superior and inferior grains in super rice by using semi-thin section, X-ray diffraction, and other related technologies. Superior grain filling was a continuous process, whereas inferior grain started at 8-10 days after anthesis. The order of starch accumulation starts at the central endosperm near the abdomen, followed by the endosperm of the proximal vascular bundle and finally the aleurone layer of the abdomen. Compared with the inferior grain, the superior grain featured a higher 1000-grain weight, apparent amylose content, total starch content, average starch granule size, relative crystallinity, solubility, and a resonance peak ratio at 1022/995 cm-1 , whereas the swelling power and the ratio of resonance peak at 1045/1022 cm-1 were lower. The final hydrolysis degrees of HCl, AAG and PPA of the superior grain were significantly lower than those of the inferior grain. The findings indicated that the different physicochemical properties of starch were mainly due to the development order of superior and inferior grains and the spatial enrichment of starch.