硅调控水稻耐盐性的生理与分子机制

Rice is a moderate salt-tolerant cereal crop, and also a silicon-hyperaccumulating plant species. The tolerance of rice to salt is interlinked closely to uptake and accumulcation of silicon (Si) in rice plants. It has been well-documented that silicon addition can enhance salt tolerance in rice, however, its mechanisms underpinning is still ambiguous. This project will deal with the physiological and molecular mechanisms of silicon-mediated tolerance to salt stress in rice, and is therefore of cruicial importance theoretically. In addition, the implementation of this project is also of practical importance to regulate salt tolerance in rice and increase the yield of rice by applying silicon fertilizer. The major contents of this project include the Si-mediated effects in salt-stressed rice plant on: 1) uptake and transport, distribution and compartmentalization of salt ions, potassium and calcium; 2) biosynthesis and metabolisms of small-molecule osmotic compounds; 3)change of levels of endogenous plant hormones such as ABA and GA; 4）differential expression of genes encoding for the relevant enzymes responsible for the biochemical processes above. The objectives of this project are to unravel the physiological and molecular mechanims of Si-mediated enhancement of salt tolerance in rice plants by linking these Si-induced changes at physiological and gene levels to salt tolerance. This will provide a theoretical and practical basis for extensively applying Si fertilizer to paddy rice grown on sallinized soils to obtain high yield and quality.

水稻是中度耐盐的谷类作物，也是硅超积累植物，其耐盐性与硅吸收积累呈密切的内在关联。业已证明，硅能提高水稻的耐盐性。但其机制，尤其是分子机制不清楚。本项目拟研究硅对水稻耐盐性调控的生理与分子机理，具有重要理论意义，对于利用硅肥调控水稻耐盐性、提高产量也具有实际意义。本项目拟拟从硅对盐胁迫下水稻盐分离子、钾和钙离子吸收、转运、分布与区隔化，小分子渗透调节物质的合成与代谢、内源激素如ABA 和GA等调控相关的过程入手，研究硅调控盐胁迫水稻体内这些生理过程及其编码相关酶的基因的表达差异的影响，从而揭示硅对水稻耐盐性调控的生理与分子机理。分析这些受硅调控的生理与基因水平上的差异与水稻耐盐性的关系。为生产上推广水稻施用硅肥提高盐渍化稻田水稻的产量与品质提供理论基础与实用技术。

盐胁迫是最主要的非生物胁迫之一，也是限制水稻生长和引起产量降低的重要原因。硅已被证明可以在多种植物中缓解盐胁迫，但是其机制特别是分子机制仍不清楚。本项目研究内容包括硅对水稻盐胁迫下盐分离子吸收、转运、积累与分布特征的影响；硅对水稻盐胁迫下水分平衡与渗透调节物质代谢的影响；硅对水稻盐胁迫下内源激素的影响；以期从生理与分子水平上探究硅提高水稻耐盐性的机制。在离子平衡方面，我们发现硅可以调控包括Na外排基因OsSOS1，液泡Na区隔基因OsNHX1，OsNHX3，OsNHX5，K吸收基因OsHAK1、OsHAK7、OsHAK11、OsHAK12以及K装载基因OsSKOR的表达，从而调控盐胁迫下水稻Na吸收、转运与分布，进而在水稻中缓解离子毒害。在进一步研究中，我们结合运用水稻突变体、X-射线能谱、基因表达检测等技术手段，发现硅在水稻根内皮层沉积可以阻隔盐胁迫下水稻根内的质外体途径Na转运，从而缓解盐胁迫；硅在内皮层的沉积是由硅转运蛋白OsLsi1与OsLsi2协作介导；同时地上部硅积累可以通过调控地下部硅转运基因的表达从而影响根内皮层硅沉积。利用盐胁迫与渗透胁迫（PEG）的对比，研究了硅在水稻盐胁迫下对离子毒害和渗透胁迫的响应机制，我们发现硅在地上部缓解了离子胁迫与渗透胁迫，在地下部主要缓解了渗透胁迫；硅对渗透胁迫的缓解主要是通过改善根形态结构、降低根渗透势来增加水分吸收，同时提高蒸腾来增加水分转运。另外，硅对水稻盐胁迫下会降低地上部ABA含量，而在地下部会增加ABA的含量。综合以上结果，我们从生理和分子层面阐述了硅缓解水稻盐胁迫的机制，这对于我们更好的理解硅在植物中的作用和硅肥的推广起到了重要作用。