Suriyasak Chetphilin, Harano Keisuke, Tanamachi Koichiro, Matsuo Kazuhiro, Tamada Aina, Iwaya-Inoue Mari, Ishibashi Yushi
Laboratory of Crop Science, Department of Bioresource Science, School of Agriculture, Kyushu University, Hakozaki 6-10-1, Fukuoka 812-8581, Japan.
Laboratory of Crop Science, Department of Bioresource Science, School of Agriculture, Kyushu University, Hakozaki 6-10-1, Fukuoka 812-8581, Japan.
J Plant Physiol. 2017 Sep;216:52-57. doi: 10.1016/j.jplph.2017.05.015. Epub 2017 May 24.
Heat stress during grain filling increases rice grain chalkiness due to increased activity of α-amylase, which hydrolyzes starch. In rice and barley seeds, reactive oxygen species (ROS) produced after imbibition induce α-amylase activity via regulation of gibberellin (GA) and abscisic acid (ABA) levels during seed germination. Here, we examined whether ROS is involved in induction of grain chalkiness by α-amylase in developing rice grains under heat stress. To elucidate the role of ROS in grain chalkiness, we grew post-anthesis rice plants (Oryza sativa L. cv. Koshihikari) under control (25°C) or heat stress (30°C) conditions with or without antioxidant (dithiothreitol) treatment. The developing grains were analyzed for expression of NADPH oxidases, GA biosynthesis genes (OsGA3ox1, OsGA20ox1), ABA catabolism genes (OsABA8'OH1, OsABA8'OH2) and an α-amylase gene (OsAmy3E), endogenous HO content and the grain quality. In grains exposed to heat stress, the expression of NADPH oxidase genes (especially, OsRbohB, OsRbohD, OsRbohF and OsRbohI) and the ROS content increased. Heat stress also increased the expression of OsGA3ox1, OsGA20ox1, OsABA8'OH1, OsABA8'OH2 and OsAmy3E. On the other hand, dithiothreitol treatment reduced the effects of heat stress on the expression of these genes and significantly reduced grain chalkiness induced by heat stress. These results suggest that, similar to cereal seed germination mechanism, ROS produced under heat stress is involved in α-amylase induction in maturating rice grains through GA/ABA metabolism, and consequently caused grain chalkiness.
灌浆期的热胁迫会因α-淀粉酶活性增加而提高水稻籽粒的垩白度，α-淀粉酶会水解淀粉。在水稻和大麦种子中，吸胀后产生的活性氧（ROS）通过在种子萌发期间调节赤霉素（GA）和脱落酸（ABA）水平来诱导α-淀粉酶活性。在此，我们研究了在热胁迫下发育中的水稻籽粒中，ROS是否参与α-淀粉酶诱导的籽粒垩白形成。为了阐明ROS在籽粒垩白形成中的作用，我们在对照（25℃）或热胁迫（30℃）条件下，对花后水稻植株（粳稻品种越光）进行了有无抗氧化剂（二硫苏糖醇）处理的试验。对发育中的籽粒进行了NADPH氧化酶、GA生物合成基因（OsGA3ox1、OsGA20ox1）、ABA分解代谢基因（OsABA8'OH1、OsABA8'OH2）和α-淀粉酶基因（OsAmy3E）的表达分析、内源HO含量及籽粒品质分析。在遭受热胁迫的籽粒中，NADPH氧化酶基因（尤其是OsRbohB、OsRbohD、OsRbohF和OsRbohI）的表达及ROS含量增加。热胁迫还增加了OsGA3ox1、OsGA20ox1、OsABA8'OH1、OsABA8'OH2和OsAmy3E的表达。另一方面，二硫苏糖醇处理降低了热胁迫对这些基因表达的影响，并显著降低了热胁迫诱导的籽粒垩白度。这些结果表明，与谷物种子萌发机制相似，热胁迫下产生的ROS通过GA/ABA代谢参与成熟水稻籽粒中α-淀粉酶的诱导，进而导致籽粒垩白。
