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An early-maturity indica rice variety Zhefu 49, whose grain quality and starch structure are sensitive to environmental temperature, was subjected to different temperatures (32°C for high temperature and 22°C for optimum temperature) at the grain filling stage in plant growth chambers, and the different expressions of three isoform genes ( SBEI, SBEIII and SBEIV ) encoding starch branching enzyme (SBE) in the endosperms were studied by the real-time fluorescence quantitative PCR (FQ-PCR) method. Effects of high temperature on the SBE expression in developing rice endosperms were isoform-dependent. High temperature significantly down-regulated the expressions of SBEI and SBEIII , while up-regulated the expression of SBEIV . Compared with SBEIV and SBEIII , the expression of SBEI gene in Zhefu 49 rice endosperms was more sensitive to temperature variation at the grain filling stage. This study indicates that changes in weather/climate conditions especially temperature stress influence rice grain formation and its quality as evidenced by isoform expression.

Under mean daily temperature of 32°C (high temperature) and 22°C (normal temperature) controlled in growth chambers, the expression responses of 8 soluble starch synthase (SSS) isoform genes involving starch synthesis metabolism in rice ( Oryza sativa L.) endosperms were detected using real-time fluorescence quantitative PCR (FQ-PCR). The expression patterns of SSS genes under high temperature stress were isoform-dependent, in which some isoform genes, such as SSS IIb, SSS IIc, SSS IIIb, and SSS IVa, were up-regulated with relatively high expression levels, and other genes, such as SSS IIa and SSS IIIa, showed down-regulated patterns with relatively low expression levels. SSS I and SSS IIIa were highly expressed in rice endosperms during the whole filling period in both temperature treatments, implying that they are the major isoform genes of SSS. The expressions of SSS IIb, SSS IIIa, and SSS IVa genes were much more sensitive to high temperature stress than those of SSS I, SSS IIc, SSS IIIb, and SSS IVb.

To identify the effects of grain phytic acid (PA) mutant on rice (Oryza sativa L.) grain filling and grain weight, the accumulating patterns of grain PA, total starch contents and also in relation with the carbohydrate translocation in different organs (leaf, culm, and sheath), and the activities of some enzymes involved in starch synthesis metabolism were investigated using 2 early indica genotypes differing in grain PA content-namely Xieqingzao and its low PA mutant (Os-lpa1). Compared with Xieqingzao, os-lpa1 had higher starch content and more carbohydrate accumulations in flag leaf, culm, and sheath, but much lower activities of ADPG pyrophosphorylase (ADPG-Ppase) and starch phosphorylase (SPase) in grains at filling stage, leading relatively decreasing grain weight, low grain starch accumulation and poor plumpness for os-lpa1. The activities of phosphate synthase (SP) and fructose biphosphorylase (FBPase) in sheath were generally lower at filling stage for os-lpa1 than those for Xieqingzao, despite relatively high starch content and sucrose accumulations in culm and sheath being shown for os-lpa1, implying that an obstacle of carbohydrate translocation from culm and sheath to grain at rice filling stage could be caused by grain PA mutagenesis, which might be one of major reasons for its poor plumpness and the reducing yield levels of os-lpa1.