稗草根系分泌物中水稻化感作用诱导成分分析及其诱导机理研究

Paddy weed is a major yield - limiting factor in rice production. Even at a ratio of 100 rice plants to 10 barnyardgrass plant, rice biomass is reduced by 75 % and yield lessened by about 50 %. Synthetic herbicides are the main tool available for weed control nowadays and will be used more and more. Due to the negative effects of synthetic herbicides, such as herbicide-resistant weeds, environmental contamination, and human health problems, there have been considerable efforts in designing alternative weed management strategies. Improving the inhibiting potential of rice seedlings on paddy weeds is considered as a good weed management pathway for reducing usage of synthetic herbicides and preserving the ecological environment. It has been proved that rice allelopathy is a quantitative inherit characteristic and could be increased by environment conditions or exogenous chemicals. Our preliminary results showed that the inhibitory rate of rice on barnyardgrass could be increased by 15-20 % induced by barnyardgrass root exudates, contrast to the control. However, what is/are the inductive components in the barnyardgrass root exudates, and how the inducing mechanism of rice allelopathy enhancement is still unclear. In this program, (1) the chemical components of barnyardgrass root exudates will be isolated, analyzed and identified by phytochemistry protocol, such as special resins for absorption, elution and isolation, and modern instruments including GC-MS、LC-MS、HSCCC et al. for isolation, analysis and identification. Then the allelopathic rice accession PI312777 and non-allelopathic rice accession Lemont will be chosen as targets for induction, and barnyardgrass as a target weed for bioassay. The inductive effect of chemical components isolating from barnyardgrass root exudates will be testified one by one, by bioassay-tracking protocol. The principal and synergistic compositions of inductive components will be analyzed by orthogonal experiment. Further, the inductive optimum combination will be obtained. (2) By the inductive optimum combination, 3 allelopathy rice accessions and 5 non allelopathy rice accessions will be chosen as test materials, the dose effect and time effect of the inductive optimum combination will be explored by bioassay-tracking protocol. (3) By the inductive optimum combination, the physiological and biochemical index of rice seedlings will be detected. The differential expression of genes related to phenolic and terpenoid biosynthesis pathways will be detected by qRT-PCR. The contents of phenolic compounds and terpenoids in rice will be analyzed by GC-MS and LC-MS. Thus the response mechanism of rice to induction will be elucidated. Understanding the inductive components in the barnyardgrass root exudates and the inducing mechanism of rice allelopathy enhancement could help us to enhance the rice compete to paddy weeds by inductive method, thereby lessen the dependence on synthetic herbicides in rice practice.

杂草危害是当前水稻减产的主要因素，除草剂是世界各国农业生产中防除杂草的最主要措施，然而其负面作用引起了社会和政府的广泛关注。预实验证实在稗草根系分泌物诱导下水稻抑草能力提高了15-30%。本研究主要内容为(1)通过特异树脂吸附洗脱分离结合GC-MS、LC-MS、HSCCC等仪器，对稗草根系分泌物的化学成分进行分离分析鉴定；以化感水稻PI312777和非化感水稻Lemont为诱导对象，抑草活性跟踪验证各组分的诱导抑草效果；通过正交旋转回归实验，明确诱导物质主成分和协同成分，获得最优诱导组合；(2)选择3个化感水稻和5个常规水稻品种，考察最优诱导组合的剂量效应与时间效应，探明品种-剂量-时间之间的关系；(3)从水稻生理生化指标、qRT-PCR检测的基因表达差异程度和代谢产物检测进行互相比较验证，阐明水稻响应稗草根系分泌物诱导的生理生化与分子机制，为筛选和选育高诱导响应之化感水稻品种提供科学依据

使用除草剂是水稻生产中控制农田杂草的主要方式，除草剂的长期和过量使用带来的环境问题引起各国政府的高度重视。化感水稻通过自身释放的化感物质抑制农田杂草，成为可供开发利用的综合控草方法之一。本项目从稗草和水稻之间的化学通讯入手，从稗草根系分泌物中寻找可提高水稻抑草能力的诱导物质，研究水稻诱导响应机制。结果表明：1. 稗草根系分泌物能有效诱导化感水稻PI312777和非化感水稻Lemont的叶片浸提液、种植液对莴苣、稗草的生长抑制作用，诱导具有剂量效应和时间效应，诱导剂量以1株水稻/1.5株稗草根系分泌物，诱导时间2天为最佳；2. 稗草根系分泌物中的水杨酸具有最强的诱导效果，2.0μg水杨酸/2L种植液可将3叶期水稻的诱导化感作用近2倍（与未诱导水稻比较）；3. 稗草根系分泌物的非极性树脂吸附洗脱液具有很好的诱导效果，75mL洗脱液/5L种植液可将3叶期水稻的提高2倍多（与未诱导水稻比较）；4. 诱导处理下水稻的根长株高和干物质重增加，叶片中保护酶（SOD、CAT、POD、）和叶绿素含量上升，代谢产物（可溶性糖、可溶性蛋白、脯氨酸等）增加，而丙二醛含量（MDA）下降；5. 荧光定量PCR结果显示，诱导后化感水稻、非化感水稻和常规稻的叶片中与光合作用、营养吸收利用、酚酸类代谢途径（苯丙氨酸代谢途径）、萜类代谢途径（MVA代谢途径），以及外源物质脱毒作用相关的27个基因表达呈现不一样的变化。6. 诱导后水稻根系的转录组测序、基因表达和蛋白质功能分析表明，水稻响应稗草根系分泌物诱导的机制主要涉及乙酸代谢途径、苯丙氨酸代谢途径、萜类骨架生物合成，以及激素信号识别与转导途径等。其中苯丙氨酸基因是启动表达后续分子机制的关键环节。研究证实了通过化学物质外源诱导可以有效提高水稻抑草能力。围绕代谢途径中的基因表达和蛋白质表达，寻找合适的诱导物质和诱导途径，进一步提高水稻诱导抑草作用，可以大大减少除草剂的使用，有利于稻田土壤的可持续利用，保护农田生态环境，具有重要的科学意义和应用前景。

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