Characterizing genetic & soil induced variation in arsenic uptake translocation & metabolism in rice to mitigate arsenic contamination in Asia

大米是东南亚人的主食。水稻从土壤中吸收的砷比其他粮食作物多，因为它是厌氧栽培，而不是好氧栽培。厌氧培养导致更大的砷动员，因此更大的植物可利用性。即使在大米中砷的背景水平，大米对人类饮食中这种致癌元素的暴露也有很大贡献。不幸的是，水稻产区的大片土地受到污染，原因是稻田灌溉的地下水砷含量升高，以及碱金属和贵金属活动产生的废水造成污染。例如，灌溉用水污染导致大约4000万孟加拉国人的水稻受到污染，而2000万中国人因采矿污染而依赖砷污染的稻田。在这些受污染的土壤上，稻米中的砷含量会大幅上升，从而大大增加了从饮食中摄入砷的机会。土壤污染的程度和性质意味着不可能从这些土壤中去除砷，而且，鉴于这些农业生态系统所支持的高人口密度，受污染的土壤仍必须用于水稻生产。通过初步试验，我们发现水稻对砷的吸收、运输和代谢存在相当大的遗传变异。该项目将确定导致这种变异的基因，并将它们定位在水稻基因组上，以便培育出低砷含量的水稻，其中高比例的砷是毒性较低的有机品种。将在孟加拉国、西孟加拉邦和中国进行实地试验，以确定在地下水和矿井污染土壤上种植的植物的当地适应物种中存在的砷颗粒吸收和代谢的变化，以便为进一步育种进行选择。这些试验将包括绘制其父母在砷吸收和代谢方面存在差异的群体的图谱，并通过遗传分析，确定和表征导致具有更理想代谢物的低粒砷性状的基因。这种遗传信息还将使水稻的育种具有适合在砷污染的土壤上使用的特性。还将调查影响水稻对砷吸收的土壤因素，以确定管理措施是否也可以降低砷在水稻中的积累。

Rice is the dietary staple of South East Asia. Rice assimilates much more arsenic from soils that other grain crops as it is cultivated anaerobically, rather than aerobically. Anaerobic cultivation leads to much greater arsenic mobilization, and thus greater plant availability. Even at background levels of arsenic in rice, rice contributes considerably to human dietary exposure of this carcinogenic element. Unfortunately, extensive areas of land in rice producing regions have been contaminated through irrigation of paddy fields with groundwaters elevated in arsenic and through contamination from wastewater from base and precious metal activities. For example, irrigation water contamination has resulted in the contamination of rice of around 40 million Bangladeshis, whilst 20 million Chinese are dependent on arsenic contaminated paddies as a result of pollution from mining. On these contaminated soils, levels of arsenic can rise considerably in rice grain, greatly increasing dietary exposure to arsenic. The extent and nature of the soil contamination mean that it is not possible to remove arsenic from these soils, and also, given the high population densities supported by these agroecosystems, the contaminated soils must still be kept in rice production. Through initial trials we have revealed that there is considerable genetic variation in arsenic uptake, transport and metabolism in rice. This project will identify the genes responsible for this variation and locate them on the rice genome to enable rice to be bred that has low grain arsenic levels, with a high proportion of this grain arsenic being present as less toxic organic species. Field experiments will be conducted in Bangladesh, West Bengal and China to determine the variation in arsenic grain uptake and metabolism that exists in locally adapted species for plants grown both on groundwater and mine contaminated soils, to enable selection for further breeding. These trials will include mapping populations whose parents differ in arsenic uptake and metabolism, and through genetic analysis, the genes responsible for traits leading to low grain arsenic with more desirable metabolites will be identified and characterised. This genetic information will also enable breeding of rice with characteristics that make it suitable for use on arsenic contaminated soils. Soil factors affecting arsenic uptake by rice will also be investigated to determine if management practices can also lower the arsenic accumulation into rice grain.