叶施氧化硅溶胶抑制水稻砷吸收转运的生理机制

It has been received widespread attention that silicon fertilizer application could alleviate heavy metal toxicity to plant, but few studies have been carried out with silicon sol foliar application to reduce heavy metal uptake and accumulation in plant. According to large number of our previous researches with hydroponic experiments, pot experiments and field experiments, the silicon sol foliar application could significantly alleviate arsenic toxicity to rice and significantly reduce arsenic accumulation in rice grain. The objectives of present project are: (1) to study the Si uptake by rice leaves and its distribution in rice by using the 30Si stable isotope, and to analyze the effect of silicon sol foliar application on As uptake and accumulation in rice; (2) to research the effect of silicon sol foliar application on microstructure and sub-microstructure of shoots or roots of rice under arsenic stress, and to regionalize the subcellular location of As and Si by using electron probe microanalysis; (3) to measure the overall capacity of apoplastic transport of rice root by using apoplastic fluorescence tracer PTS (tri-sodium-8-hydroxy-1, 3, 6-pyrenesulphonate), and to determine the amount of As transport from root to shoot through apoplast bypass flow with or without silicon sol foliar application; (4)to investigate the rice Si gene Oslsi1 and Oslsi2 expression level in rice root with different dose of silicon sol foliar application, and to reveal the genetic modification mechanism of silicon sol foliar application on reduction arsenic uptake and transport in rice. Insights on the mechanism of reduction arsenic accumulation in rice and useful information of effective way to deal with the contamination of arsenic could be better understood with the project implement.

土壤施用硅肥可以提高植物抗重金属毒害能力已经受到了广泛关注；但叶施氧化硅溶胶抑制植物吸收积累重金属的报道不多。我们前期大量的水培、土培与大田试验证实，叶施氧化硅溶胶能显著抑制稻米砷积累，缓解砷毒害。本项目将以水稻为研究材料，采用硅稳定性同位素示踪技术研究水稻叶片硅吸收和硅在体内的分布，分析其对水稻砷吸收转运的影响；电镜技术分析叶面施硅对砷胁迫下水稻组织、细胞结构的影响，电子探针技术分析叶面施硅的水稻体内硅砷分布效应，荧光标记技术研究叶面施硅对砷质外体转运途径的影响，揭示其抑制水稻砷吸收转运的组织学与细胞学机理；采用定量RT-PCR技术研究叶面施硅对水稻根系硅转运基因OsLsi1和OSLsi2表达的抑制效应，进一步探讨这种抑制效应对砷吸收转运的影响，揭示其抑制水稻砷吸收转运的分子生物学机制。为减少稻米砷积累提供理论依据，具有重要的水稻生理生态学意义。

水培条件下研究了叶面施氧化硅溶胶对水稻砷吸收转运的影响，结果表明在100 μM Na2HAsO4处理下，叶面施硅使水稻地上部和根系砷浓度分别降低41.3%和22.3%，水稻幼苗地上部砷积累量降低30.0%；叶面施硅处理对砷胁迫下水稻幼苗根系和地上部细胞壁砷含量并没有显著影响；但可以显著提高水稻幼苗地上部细胞壁砷百分比。100 μM Na2HAsO4胁迫下，叶面施硅水稻根系SOD、POD、APX活性分别增加了54.0%、41.9%、16.8%；而MDA、ELR降低了130.2%、33.8%。叶面施硅可以显著提高砷胁迫下水稻抗氧化系统功能，从而缓解砷胁迫对水稻的氧化损伤，这可能是叶面施硅缓解水稻砷毒害的一个主要机制。叶面施硅可以抑制根系砷吸收转运基因OLis1、OLis2，以及茎秆再分配过程基因OLis6活性，从而抑制其向地上部运输；这可能是叶面施硅抑制水稻砷吸收积累的机制之一。同时叶面施硅可以降低根系对质外体荧光指示剂PST的吸收，这表明，叶面施硅可以降低砷胁迫下水稻根系质外体通透性，从而影响As通过质外体途径向地上部运输；这也可能是叶面施硅降低水稻砷积累的机制之一。这些研究结果为叶面施硅治理稻米砷污染提供了理论依据。. 同时我们分析了莲花山矿区73个稻田土壤有效硅含量及其对稻米砷积累的影响。结果表明，土壤有效硅含量平均为40.72 mg kg-1，硅是植物有益元素，由于华南稻田有效硅缺乏，而土壤有效硅含量与稻米砷含量呈现极显著正相关关系，因此通过叶面施硅，可以补充土壤有效硅不足抑制稻米砷积累。在此基础上，研制了硒硅复合溶胶，通过盆栽和大田试验研究了其对水稻砷吸收积累的影响，开发了能治理稻田砷污染的叶面阻隔剂。研究结果显示，叶面喷施硒掺杂纳米硅溶胶可以有效提高盆栽水稻籽粒的生物量降低籽粒砷含量提高硒含量，另外大田试验结果也显示叶面喷施硒掺杂纳米硅溶胶后能有效降低籽粒的砷积累提高硒吸收。为我国砷污染稻田治理提供了新出路。