ABA Affects Distinctive Rice Caryopses Physicochemical Properties on Different Branches

Abscisic acid (ABA) plays an important regulatory role in the grain filling process, which in turn will affect the final yield and quality of rice. The ABA biosynthesis genes of <i>OsNCED3</i> and degradation gene <i>OsABA8ox3</i> affect the ABA content, and then further regulate the ABA signaling. During the development of rice panicle, compared with primary grains (superior grains) growing on primary branches, secondary grains (inferior grains) growing on secondary branches exhibit characteristics. However, little is reported on the physicochemical characteristics of starch between superior and inferior grains in ABA related transgenic lines. In this study, <i>OsNCED3</i> and <i>OsABA8ox3</i> transgenic plants were used as materials. The results showed that compared with the WT, the <i>OsNCED3-RNAi</i> lines on grain weight was consistent with the trend of superior and inferior grains, while the <i>OsABA8ox3-RNAi</i> lines affected superior or inferior grains. The total starch and soluble sugar content of grains decreased in both <i>OsNCED3-RNAi</i> and <i>OsABA8ox3-RNAi</i> lines, and the total starch content of superior and inferior grains in <i>OsABA8ox3-RNAi</i> lines decreased. The starch granule size distribution of all samples showed a bimodal and increased proportion of starch grains with large granule size, in which the influence on inferior grains was greater than that of superior grains, which eventually led to a significant increase in their average granule size. The apparent amylose content of inferior grains increased significantly in most lines. The swelling power of the superior grains decreased significantly, while that of the inferior grains increased significantly. Fourier analysis showed that the order degree of starch granule surface decreased in the superior grains of the RNAi line, while it increased in the inferior grains of the <i>OsABA8ox3-RNAi</i> line but decreased in the <i>OsNCED3-RNAi</i> lines. In the superior grains, the relative crystallinity of starch decreased in the <i>OsNCED3-RNAi</i> lines, but remained unchanged or increased in the <i>OsABA8ox3-RNAi</i> line. In inferior grains, the relative crystallinity of starch decreased in the ABA synthesis RNAi line, but increased in the <i>OsABA8ox3-RNAi</i> line. In summary, the influence of ABA on the physicochemical properties of inferior grains is greater than that of superior grains.