渗氧对水稻砷吸收的影响及调控研究

Arsenic (As) contamination is currently an environmental problem that has been receiving increasing concern. Substantial As contamination of paddy soil has now been found in China, and has adversely affected the health of millions of people that relies on rice as a staple food source. Therefore, there is an urgency to understand the mechanism of As tolerance and uptake by rice. The results of present proposal may be very valuable in revealing and explaining the physiological mechanisms of As uptake by rice, and can potentially provide valuable information in screening and breeding rice with low concentrations of As in their grains. Wetland plants including rice have adapted to waterlogged conditions by developing extensive aerenchyma in their roots. Rice roots constitutively form aerenchyma, and the amount is enhanced by waterlogging or oxygen-deficient conditions; porosity (gas volume/tissue volume) in plant tissues results from the intercellular gas-filled space formed as a constitutive part of development, which is enhanced by the formation of aerenchyma. In roots, oxygen is obviously required for respiration to provide sufficient energy for growth, maintenance, and nutrient uptake processes, and up to 30-40% of the oxygen supplied via the root aerenchyma is being lost to the soil, a process called radial oxygen loss (ROL). Formation of aerenchyma and ROL presumably contribute to the waterlogging tolerance of rice. Moreover, it is considered that ROL from root to the rhizosphere is essential for the detoxification of phytotoxins such as heavy metals by direct oxidation or by the agency of oxidizing aerobic microorganisms maintained in the rhizosphere regions. It is reported that there were negative correlations between ROL and As accumulation in aboveground parts of rice especially inorganic As in grains. Environmental factors such as growth conditions, other compounds in soils such as sulfur and organic acids could affect ROL. It is reported that different growth conditions such as flooding and aerated conditions, and silicate fertilizer could affect As tolerance and accumulation in rice. The aim of the present proposal is to investigate the effects of silicate fertilizer on ROL and As accumulation in rice with flooded and aerated conditions, and As behavior in rhizosphere and As species transportation in rice plants in flooded and aerated conditions, and to evaluate the possibilities on application in rice fields to finally reduce the health risks posed by As contamination in rice.

水稻是我国第一大粮食作物，砷污染严重影响稻米的产量和品质，危及人体健康。稻米砷污染问题已成为我国比较突出且急需解决的重要环境问题之一。水稻的通气组织和渗氧是其适应稻田湿地环境的决定因素，水稻的渗氧能力跟水稻地上部分砷（尤其是谷粒）的吸收以及谷粒无机砷含量成反比，调控环境因素可影响水稻的渗氧能力。本项目的研究基于对土壤水分条件和土壤硅含量等水稻砷吸收影响因素的探讨，分析土壤水分条件和硅对根的渗氧量（率）和孔隙度的影响及其作用机制，及其与砷在水稻的根际行为和砷在水稻体内形态和迁移转化之间的关系，找出提高水稻渗氧量（率）的方法，进而通过提高水稻的渗氧能力来减少水稻砷的吸收和积累，为砷低积累、高耐性的水稻品种在中低污染土壤的田间种植，减少可食谷粒中砷含量，降低水稻砷污染造成的健康风险提供理论依据。

水稻是我国第一大粮食作物，砷污染严重影响稻米的产量和品质，危及人体健康。稻米砷污染问题已成为我国比较突出且急需解决的重要环境问题之一。本研究以6个不同水稻品种，包含杂交稻和常规稻，为研究对象，研究不同渗氧能力水稻品种砷（As）吸收、积累和形态，硅（Si）对水稻根际砷迁移的影响，以及Si对水稻As吸收、积累和形态的影响，探讨硅对水稻砷吸收的影响及其机制，为筛选低As积累的水稻品种提供了依据，为砷低积累、高耐性的水稻品种在中低污染土壤的田间种植，减少可食谷粒中砷含量，最终降低水稻砷污染造成的健康风险提供了理论和应用基础。通过研究取得如下主要成果：1）6个水稻品种的渗氧能力存在显著差异（P<0.01），常规稻的渗氧能力显著高于杂交稻（P<0.01）。湘丰优9号的渗氧率最低，为9.55 μmol O2 •g-1 DW•h-1；湘晚籼12号的渗氧率最高，为27 μmolμmol O2 •g-1 DW•h-1。2）不同渗氧能力水稻品种地上部和地下部的As含量均存在显著差异（P<0.001），高渗氧水稻品种地上部的砷含量低于低渗氧水稻品种，硅显著降低了水稻地上部和地下部As含量（P<0.001）。相比不加Si处理，水稻地上部的无机As含量在加Si处理下降低了24-31%。3）加Si处理降低了土壤残渣态As，增加了特异性吸附态As。相比不加Si处理，加Si处理后根际土壤中特异性吸附态As升高了12-36%，无定形铁铝氧化物结合态As含量降低了10-19%，结晶铁铝氧化物结合态As含量降低了26-33%，残渣态As含量降低了17-35%。4）不同渗氧能力水稻品种根表铁膜中铁（Fe）含量存在显著差异（P<0.01），高渗氧水稻品种根表铁膜中Fe含量高于低渗氧水稻品种，铁膜中As含量与Fe含量呈显著正相关（P<0.005），加Si处理显著增加了水稻根表铁膜中Fe含量（P<0.05）。5）加硅处理显著降低了水稻根部、秸秆和谷壳的砷含量（P<0.05）。相比不加硅处理，水稻籽粒的砷含量在加硅处理后下降了40-42%。相比不加硅处理，水稻秸秆无机砷含量在加硅处理后降低了28-60%；谷壳中的无机砷含量降低了55%，DMA含量降低了27-44%；籽粒中的无机砷含量降低了16-19%，DMA含量降低了15-58%。