茉莉酸调控稗草干扰水稻米质形成的差异性机理

Previous studies had showed that the effect of barnyardgrass interspecies on rice quality formation existed in a significant difference; meanwhile, we also found that the jasmonic acid contents in rice plants had differences among different varieties of barnyardgrass, but the foundation of endogenous jasmonic acid in rice on grain quality is unknown so far. In this study, jasmonic acid content of rice root, leaf and panicle, jasmonic acid activity and the expression levels of transcription factor MYC2 at rice growth critical stages are firstly identified when we use three barnyargrass varieties Echinochloa. crus-galli var. mitis, Echinochloa crus-galli. crusgali var. zelayensis, and Echinochloa colonum, and a rice variety, ning 9108, as materials, then rice photosynthetic rate, root oxidation activity, the contents of five major classes of hormones including cytokinin etc, the dynamic changes of key enzyme activities in sucrose-starch metabolic pathways during grain filling stage of rice are analyzed. Finally, the expression characteristics of rice chalk5 and endosperm Wx genes during the grain filling stage are explored and the expression function analysis of chalk5 and Wx were verified through the ibuprofen (biosynthesis inhibitor) and jasmonic acid treatment, moreover, the quality parameters of mature rice that potential impacted by these two important regulation factors are also determined. The results of the above might reveal the difference mechanism of inter-barnyardgrass interference with rice quality formation, and discover the function of jasmonic acid in the cultivation of better quality rice, all of which would provide a new strategy and broad application prospect for the green management of weeds in rice fields and the development of new technologies for improving rice quality.

前期研究发现稗草种间影响水稻米质的差异显著，同时稗草引起的水稻植株茉莉酸含量也存在显著的种间差异。但水稻内源茉莉酸在水稻米质形成过程中起何种功能？人们知之甚少。本项目拟以无芒稗、西来稗、光头稗和水稻宁9108为材料，设计供试稗草与水稻四种共生处理，采用植物生理学与分子生物学的研究手段，首先明确水稻生育关键时期水稻根、叶、穗茉莉酸含量、茉莉酸合成酶基因与转录因子MYC2的基因表达量；然后分析灌浆成熟期水稻光合速率、根系氧化力、细胞分裂素等五类激素含量、淀粉合成相关酶活性变化动态；最后探明各处理灌浆成熟期水稻垩白基因Chalk5与胚乳Wx基因表达特征，并通过茉莉酸合成抑制剂布洛芬与茉莉酸处理，验证Chalk5与Wx基因表达变化，测定稻米品质参数。以上研究结果可揭示茉莉酸调控稗草种间干扰稻米品质形成机理的差异性，为制定绿色治理稻田杂草的新策略与发掘提高稻米品质的新技术提供科学依据、应用前景广阔。

稗草是稻田中最重要的恶性伴生杂草之一，显著影响了水稻的高产优质。而茉莉酸在植物生长发育中具有重要的生理功能，但对于水稻与稗草伴生过程中茉莉酸对水稻米质形成的作用机理，人们知之甚少。本项目研究了水稻与不同种稗草共生过程后水稻不同时期不同部位中茉莉酸含量的变化，及其与水稻米质的关系。结果表明：<1>、水稻与稗草共生后水稻不同时期、不同部位茉莉酸含量存在较大差异。随着生育进程水稻体内的茉莉酸含量逐渐降，且不同部位含量由大到小为根系、叶片和籽粒。在水稻分蘖中期，各处理相同部位的茉莉酸含量无显著差异，但在在其他生育时期，水稻与稗草共生后水稻体内的茉莉酸含量均显著增加，T2和T3的增加幅度显著高于T1；<2>、水稻与稗草共生后水稻的整精密率和胶稠度显著降低、垩白大小、垩白米率和垩白度显著增加，对糙米率、精米率、直链淀粉含量和蛋白质无显著影响；<3>、水稻与稗草共生后稗草对灌浆期水稻的根长密度、根量、根系总吸收面积、根系活跃面积、根系氧化力、根系和籽粒中Z+ZR含量、叶片光合速率和籽粒中蔗糖合酶、ADP-葡萄糖胶磷酸化酶和淀粉分支酶活性显著降低。相关分析表明，灌浆期不同部位的茉莉酸含量与上述指标呈极显著负相关；<4>、水稻与稗草共生后在不同生育时期分别喷施50 μmol/L茉莉酸和茉莉酸合成抑制剂，以清水为对照。结果表明，在穗分化时期喷施上述外源物质对水稻的米质无显著差异，但在灌浆期初期和穗分化时期+灌浆初期喷施茉莉酸后增加了水稻的整精米率和胶稠度，降低了垩白米率、垩白大小和垩白度，但对直链淀粉含量和蛋白质无显著影响。上述研究表明，水稻与稗草共生后水稻体内的茉莉酸含量增加，稻米品质变劣。喷施适度外源茉莉酸能改善水稻的加工品质、外观品质和蒸煮食味品质，这对拓展水稻分子设计育种具有重要指导意义。