硒对镉-砷复合污染下水稻吸收和累积镉、砷的根际调控机制

Cadmium (Cd) and Arsenic (As) are the two harmful and widespread heavy metals, and always coexist in paddy soils. Paddy rice (Oryza sativa. L) is the staple food for Chinese people, which has a greater potential for the accumulation of Cd and As than many other crops and thus is the main source of Cd and As intake. Therefore, it is urgent to reduce the content of Cd and As in rice grain, improve its quality and guarantee food safety. Selenium (Se) is an essential trace element for humans and animals. In recent years, the antagonism of Se on heavy metal stress has been observed in many different plants. This study primarily focuses on the interaction between Se and Cd-As in the rhizosphere of rice through experiments under hydroponic and soil conditions which are combined with technologies such as the extractive technique of soil solution, micro-X-ray fluorescence, and speciation analysis technique. It investigated the effects of Se on the uptake, translocation, distribution and transformation of Cd and As in Cd-As combined treatment, the effects of iron plaque and Se on Cd and As uptake and translocation by rice, to reveal the mechanisms of mediated uptake of Cd and As by rice facilitated by Se in rhizosphere. The study will provide theoretical support to reducing Cd and As content and improving Se content in rice grain.

镉和砷是农田土壤中危害较大、影响范围较广的两种重金属，且两者常常以复合污染形式出现。水稻是我国的主要粮食作物，对镉、砷的累积能力比其他作物强，成为人体镉、砷摄入的主要来源。因此，降低水稻镉、砷污染，提高稻米品质对保障粮食安全和人民身体健康具有重要的意义。硒作为一种有益元素，与重金属具有拮抗作用。本研究以硒和镉、砷的相互作用为研究主线，通过水培和土壤盆栽试验，结合土壤溶液提取、X射线荧光光谱分析（μ-XRF）、形态分析等技术方法，研究在镉-砷复合污染下，硒的添加对水稻镉、砷的吸收、转运、分配和在体内形态转化的影响以及水稻根际铁膜的形成和添加硒对水稻吸收累积镉、砷的影响，探明硒抑制水稻吸收和累积镉、砷的根际调控机制。为降低稻米中镉和砷的含量、提高稻米中硒水平技术的研发应用提供理论依据。

镉和砷在稻田中危害大、影响广，且常以复合污染形式出现。降低水稻镉、砷污染对保障粮食安全和人民身体健康具有重要意义。本研究以硒和镉、砷的相互作用为主线，通过水培和盆栽试验，结合形态分析、PCR定量、电镜扫描、土壤溶液提取等技术，研究了在镉-砷复合污染下，硒的添加对水稻镉、砷的吸收、转运、分配和形态转化的影响机制，旨在为降低稻米中镉和砷含量、提高稻米中硒水平技术的研发应用提供理论依据。结果表明：.（1）水稻根部对亚硒酸盐（SeIV）和硒酸盐（SeVI）的吸收速率相似，且显著高于纳米硒。水稻吸收的纳米硒或SeIV主要存在于根部，很少向地上部转运，而SeVI处理下硒的转运系数最高，分别是SeIV和纳米硒处理的9.1倍和48.5倍。纳米硒或SeIV处理时，水稻地上部和根部中均以硒代蛋氨酸（SeMet）为主；而SeVI处理时，则以硒酸根[Se(VI)]为主要硒形态。.（2）在镉-砷复合污染条件下，硒的供应降低了地上部和根系对镉的累积，且SeVI的降低效果优于SeIV，加硒使OsNramp1和OsNramp5的表达量降低。添加SeIV提高了水稻根部的砷含量，而添加SeVI降低了水稻根系砷含量，但对水稻地上部的砷含量均无显著影响，加硒下调了OsLsi1和 OsLsi2的表达。添加硒减少了细胞器中镉的比例，降低了OsHMA3的表达量，而对砷的占比影响不大。水稻地上部与根系中的As(III)含量高于As(V)，而硒的添加使得As(III)/As(V)的比率下降。加硒促进了水稻根系的凯氏带发育，增加了木质素含量；增加了水稻地上部和根中的GSH和NPT的含量，提高了CAT和GSH-PX的活性。.（3）无论有无铁膜生成，硒供给降低了地上部和根系中的镉含量；SeⅣ处理降低地上部的砷含量但提高根系的砷含量；SeⅥ处理与SeⅣ情况相反，对地上部砷含量没有显著影响，但降低根系砷含量。.（4）淹水和添加硒降低了土壤溶液和水稻植株中的镉含量，淹水和非淹水下加硒分别使水稻籽粒的镉含量降低了61.3%-77.4%和45.2%-46.3%。淹水增加了土壤溶液和水稻植株中的砷含量，在非淹水处理中，加硒使水稻籽粒的砷含量降低了27.5%；而在淹水条件下，硒的添加使水稻籽粒中砷的含量增加了43.7%-74.6%。