Abstract
To elucidate the effect of high temperature on grain filling metabolism, rice developing caryopsis was exposed to high temperature during milky stage. Comprehensive gene screening by 22K microarray and differential hybridization, and following expression analysis by semi-quantitative RT-PCR revealed that several starch synthesis-related genes such as GBSSI and BEIIb were down-regulated by high temperature whereas those for starch-consuming α-amylases and HSPs were up-regulated. Biochemical analyses of starch showed that the high temperature-ripened grains consisted of decreased content of amylose and long chain-enriched amylopectin, which might be attributed to repressed expression of GBSSI and BEIIb, respectively. SDS-PAGE and immunoblot analysis of storage proteins revealed decreased accumulation of 13-kD prolamin, which is consistent with diminished expression of prolamin genes under elevated temperature. Ripening under high temperature resulted occurrence of grains with chalky appearance and decreased weight. The possible metabolic pathways affected by high temperature and their relevance to grain chalkiness are discussed.
