水稻砷污染健康风险与砷代谢机制的研究

水稻是人类主要的粮食作物之一，然而，目前稻米主要生产区（东南亚地区）的土壤和灌溉水砷污染严重，导致稻米中砷的积累；砷在稻米中的积累通过食物链传递，对人体健康构成严重威胁。所以，稻米砷污染问题已成为东南亚地区比较突出且急需解决的环境问题之一，而减少水稻对砷的吸收、控制水稻体内砷向籽粒转移、降低籽粒中砷的生物有效性是解决这一问题的关键途径。因此，深入理解水稻对砷的吸收、体内转运和转化等代谢机制非常有必要。近年来有关水稻对砷的吸收和体内砷代谢机制的研究取得了很大进展。研究表明，水稻根系通过磷吸收通道吸收五价砷（As（Ⅴ）），水通道吸收三价砷（As（Ⅲ））。进入水稻体内的砷，一部分由地下部转运到地上部，其中一部分进一步被转运到水稻籽粒中。根表铁膜能抑制水稻对As（Ⅴ）的吸收和向地上部的转运。在水稻的地下部和（或）地上部还存在着As（Ⅴ）还原、As（Ⅲ）甲基化等砷形态的转化过程。最近，水稻砷酸盐还原酶基因已经被克隆和表征。

Health Risk from Consumption of Rice with Elevated Arsenic and Studies of Arsenic Metabolism in Rice Plants

Rice (Oryza sativa) is the staple food for people in many parts of the world, however, paddy soil and irrigation water of the major rice production areas (mainly in Southeast Asia) are under the severe threat of arsenic (As) contamination, resulting in an elevation of As in rice grains. Accumulated As in grains can eventually be transferred to human beings through food chain, causing serious health problems. Arsenic contamination of rice has therefore become a prominent and urgent environmental problem around the globe, particularly in Southeast Asia. How to minimize As uptake by rice, to reduce As translocation to grains, and to decrease As toxicity in grains is the key approach to solving this problem. It is therefore necessary to understand As metabolism in rice plants growing in As-contaminated paddy soils. In recent years, great progresses have been made in understanding the mechanism of As uptake by and metabolism in rice plants. It is believed that arsenate is taken up via the phosphate transport systems, and arsenite via glycerol transporting channels (or aquaporins). Once inside rice roots, some As is translocated from roots to shoots, and some is further translocated into grains. Iron plaque can inhibit arsenate uptake and its translocation to shoots and grains. Along with As translocation, transformation of As species is also occurring, such as arsenate reduction and arsenite methylation. Two rice arsenate reductase genes (OsACR2s) have been cloned and characterized recently.