硅缓解水稻铝毒的生理与分子机制

Aluminum (Al) toxicity is one of the major factors limiting the yield and quality of crops in tropical and subtropical regions; rice is a Si hyperaccumulating plant species. Silicon (Si) is shown to be effective in improving rice resistance against stressful environments. It has been well-documented that Si can significantly alleviate aluminum toxicity in crops including rice, but its relevant mechanisms, especially the molecular mechanisms, are still unknown. In this project, an aluminum-sensitive rice mutant, c68, will be used as testing material to investigate the physiological and biochemical, and, in particular, molecular mechanisms involved in Si-mediated alleviation of aluminum toxicity in rice by adopting some advanced physiological and molecular tools. The major contents of this research include: 1) morphological alterations of the outer cell layers, absorption and compartmentalization of aluminum ions in the roots of rice; 2) lignin biosynthesis of rice roots; 3) aluminum accumulation in the nodes of rice; and 4) differential expressions of genes encoding for the relevant enzymes and transporters responsible for the biochemical processes mentioned above. The objectives of this research are to unravel the physiological and molecular mechanisms involved in silicon-alleviated aluminum toxicity in rice plants by linking these Si-regulated changes at both physiological and gene levels to silicon-alleviated aluminum toxicity. This research can provide a basis for better understanding of Si-mediated alleviation of Al toxicity in rice as well as genetic improvement of rice and is thereby theoretically important. The implementation of this research can also provide a basis for applying silicon fertilizer to improve the yield and quality of rice under Al stress in southern China regions, and is therefore of great practical implications.

铝毒是热带和亚热带地区作物高产优质的主要限制因子之一。水稻是硅的超积累植物，硅在提高水稻抗逆性方面功效卓著。业已证明，硅能显著降低水稻等作物的铝毒，但是其作用机制，尤其是分子机制尚不清楚。本项目拟采用铝敏感水稻突变体c68为材料，采用植物生理生化和分子生物学手段，从（1）硅调节铝胁迫下水稻根部外细胞层形态改变，（2）水稻根部铝吸收与区隔化，（3）水稻根部木质素生物合成，（4）水稻节间铝积累等方面入手，探究硅对铝胁迫水稻体内相关生理过程及其编码相关酶或转运体的基因表达差异的影响，从而揭示硅缓解水稻铝毒的生理与分子机理，阐明这些受硅调节的生理及基因水平上的差异表达与水稻解铝毒的关系。本项目不但为阐明硅调控水稻抗铝机制及其遗传改良提供理论基础，而且对于指导我国南方地区稻田推广应用硅肥降低水稻铝毒、实现水稻高产优质具有重要实际意义。

铝毒是酸性土壤中限制作物生长的主要因子。硅能有效地缓解植物铝毒害，现已证明羟基铝硅酸盐的形成是硅缓解铝毒害的重要机制，但硅调控植物耐铝性的生理与分子机制尚不清楚。本研究选用水稻作为研究对象，通过水培试验，运用多种处理方式和技术手段，在生理与分子层面上重点研究了根边缘细胞、根尖细胞壁、根栓质化、铝转运蛋白、硅转运蛋白和硅铝互作在硅缓解水稻铝毒害中的作用，主要结果如下：.（1）铝胁迫下，硅通过增加细胞壁果胶甲基酯化程度来促进根尖边缘细胞的形成，而边缘细胞上硅铝复合物的形成降低了铝的毒性、增加了边缘细胞的存活率，从而促进了粘液的产生。边缘细胞及其粘液在根尖形成的保护鞘阻止了铝扩散到根尖，降低了根尖铝含量，缓解了水稻根尖铝胁迫。.（2）铝在细胞壁中的主要结合位点是半纤维素而非果胶，而铝在细胞壁上的积累限制了根细胞的伸长。铝胁迫下，硅通过减少OsPME在根尖中的表达降低果胶甲酯酶（PME）活性，从而增加细胞壁果胶甲基酯化程度，同时硅减少了细胞壁半纤维素的含量，两者共同导致铝在根尖细胞壁中积累的减少，促进了根伸长。.（3）铝在根中的积累可以上调木栓质合成基因在根中的表达，增强根的栓质化，从而限制根系发育，进而减少根对养分的吸收，最终抑制水稻生长。铝胁迫下，硅通过下调OsNRAT1和OsALS1在根中的表达减少铝在根中的吸收和转运，从而降低根中铝含量；相应地，根的栓质化被抑制，根系发育得到恢复，从而增加了根对养分的吸收，促进了水稻生长。.（4）铝和硅在水稻根中的互作存在一种反馈调节系统，即只有当水稻感知到铝毒害时，才会促进硅在根中的积累，从而抑制根对铝的吸收，减少铝的积累。在硅缓解水稻铝胁迫的过程中，存在明显的积极的硅铝交互作用，其能显著促进水稻生长，OsLsi2在其中发挥着重要作用。.综上，本项目较为系统地揭示了硅缓解水稻铝毒的生理与分子机制，为在酸性土壤中施用硅肥降低水稻铝毒害提供了理论基础。