The Effect of High Temperature after Anthesis on Rice Quality and Starch Granule Structure of Endosperm

To ascertain the effect mechanism of high temperature after anthesis on rice quality, the experiment was conducted with two rice lines, the heat-tolerant line 996 and heat-sensitive line 4628, with high temperature and optimal temperature in the growth chamber to investigate the effect of high temperature stress after anthesis on rice appearance quality, milling quality, cooking and eating quality and starch granule structure of endo- sperm. The result showed that milled rice rate, head rice rate, amylose content and gel consistency of both lines decreased under high temperature stress after anthesis, while the ratio of grain length to width, chalky rate, chalkiness, protein content increased. Under high temperature treatments, gelatinization temperature, final viscosity, set back and peak time increased, breakdown decreased, Mg content and K content increased, Mg/K ra- tio decreased. Under same treatment, the extent of rice quality of heat tolerant line 996 affected by high temperature was lower than that of heat sensitive line 4628. Under high temperature stress after anthesis, starch granule arranged untightly, most of starch granules existed in the form of a single starch endosperm, refractive index decreased, transparency reduced, and led to the formation of chalk. Under high temperature stress af- ter anthesis, the increase of protein content, the decrease of Mg/K, the changes of rice RVA profile characteristics and starch granule structure of endosperm could be the main reason for the decrease of rice cooking and eating quality and appearance quality.

A plastidic ATP/ADP transporter gene, IbAATP, increases starch and amylose contents and alters starch structure in transgenic sweetpotato

A plastidic adenosine triphosphate（ATP）/adenosine diphosphate（ADP） transporter（AATP） is responsible for importing ATP from the cytosol into plastids. In dicotyledonous plants, increasing ATP supply is a potential way to facilitate anabolic synthesis in heterotrophic plastids. In this study, a gene encoding the AATP protein, named Ib AATP, was isolated from sweetpotato（Ipomoea batatas（L.） Lam.）. Transcripts of Ib AATP were predominantly detected in the storage roots and leaves and were induced by exogenous sucrose and subjected to circadian rhythm. Transient expression of Ib AATP in tobacco and onion epidermal cells revealed the plastidic localization of Ib AATP. The overexpression of Ib AATP in sweetpotato significantly increased the starch and amylose contents and led to enlarged starch granules. The IbA ATP-overexpressing plants showed altered fine structure of amylopectin, which contained an increased proportion of chains with a degree of polymerization（DP） of 10–23 and a reduced number of chains with a DP of 5–9 and 24–40. In addition, starch from the transgenic plants exhibited different pasting properties. The transcript levels of starch biosynthetic genes, including Ib AGP, Ib GBSSI, Ib SSIIV, and Ib SBE, were differentially regulated in the transgenic plants. These results revealed the explicit role of Ib AATP in the starch biosynthesis of sweetpotato and indicated that this gene has the potential to be used to improve starch content and quality in sweetpotato and other plants.