| Summary: | 碩士 === 國立臺灣大學 === 農藝學研究所 === 102 === High temperature (HT) during rice grain-filling stage facilitates the formation of chalky grains, consequently influences appearance and milling quality. Formation of chalkiness has been correlated to oxidative stress, however the molecular mechanism remains unclear. Therefore, mutants (genetic background: Nipponbare) and overexpression lines (genetic background: Tainung67) of two antioxidant enzymes, Glutathion Reductase 3 (OsGR3) and Ascorbate Peroxidase 8 (OsAPX8), were investigated to reveal their roles in prevention of chalky formation in rice grains under HT. Physiological analysis on OsGR3 mutant (osgr3) reveals that HT aggravates grain filling, reduces grain weight, enhances chlorophyll degradation and increases the accumulation of H2O2 in grains. In contrast, GR overexpression line OEGR7-5 notably reduces chalky grains under HT. Leaves of OEGR7-5 also shows stay-green for a long growth period as compared to wild type (WT). In addition, OEGR7-5 maintains a high GSH/GSSG ratio under HT. In WT, HT represses expression of genes encoding starch and protein synthetic enzymes as well as antioxidant enzymes such as Glutelin synthetase, Granule-bound starch synthase, Prolamin 7, NADPH oxidase, Mn superoxide dismutase, Catalase B and Dehydroascorbate reductase. Conversely, expression of these genes were not reduced until the lately grain formation stage in OEGR7-5 under HT stress. Taken together, OsGR3 gene plays crucial roles in chalky formation of rice grains under HT by maintaining chlorophyll contents in leaves and modulating the homeostasis of antioxidative defence system. These results provide new clues about the stabilization of yield and quality of rice production under global warming condition.
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