Uptake, accumulation, and metabolic fate of thioarsenates in plants

由于自然过程和生物过程的影响，类金属砷在环境中普遍存在。砷对所有类型的生物体都是有毒的，对人类来说，它被归类为1类致癌物。砷通过转运蛋白被植物无意中吸收为必需或有益的营养素。因此，从饮食中摄取植物性食物，特别是稻米，是人类接触慢性毒性砷的主要途径。在环境中发现了不同的无机和有机砷物种。两个主要的无机砷物种通常被认为是占大部分的砷在植物中的积累是砷酸盐在氧化条件下和亚砷酸盐在还原条件下。此外，根际细菌也可以将砷甲基化，有机砷也被植物吸收。最近，我们发现，在还原性稻田条件下，无机和有机硫醇化砷（含硫砷）的存在。这些形态通常逃脱常规取样和分析方法，即使它们在各种现场条件下占总砷的很大一部分。我们的试点研究表明，植物吸收硫代砷酸盐和各自的毒性。考虑到植物砷积累与食品安全的相关性，这两个观察迫切需要一个机械的理解硫代砷酸盐对植物的影响和硫代砷酸盐对植物As负荷的贡献。拟议的项目旨在剖析植物对各种硫代砷酸盐的吸收途径、硫代砷酸盐在植物细胞内通过还原和复合物形成的代谢转化、硫代砷酸盐衍生的砷物种在植物组织之间的流动性，以及硫代砷酸盐暴露对植物砷负荷的总体贡献。研究的两个模型系统是水稻和拟南芥，水稻也是食品安全方面的主要目标生物，拟南芥是在理解砷转运和代谢方面取得许多重大突破的植物。深入了解植物与硫代砷酸盐的相互作用机制，将有助于大幅度减少作物中普遍存在的砷的积累，从而减少人类的慢性中毒。

The metalloid arsenic is ubiquitous in the environment due to both natural and anthropogenically influenced processes. Arsenic is toxic to all types of organisms and for humans it is categorized as a class 1 carcinogen. Arsenic is inadvertently taken up by plants via transporters for essential or beneficial nutrients. Therefore, dietary intake of plant-derived food and especially of rice grains is a major route for human exposure to chronically toxic arsenic. Different inorganic and organic arsenic species are found in the environment. The two main inorganic As species generally considered to account for most of the As accumulation in plants are arsenate under oxidizing conditions and arsenite under reducing conditions. Also, rhizosphere bacteria can methylate arsenic and the respective organic arsenic species are taken up by plants, too.Recently, we discovered the occurrence of inorganic and organic thiolated, i.e. sulfur-containing, arsenic species under the reducing conditions of rice paddy fields. These forms typically escape routine sampling and analysis methods even though they represent a substantial fraction of total arsenic under various field conditions. Our pilot study demonstrated plant uptake of thioarsenates and respective toxicity. Given the relevance of plant arsenic accumulation for food safety, these two observations urgently demand a mechanistic understanding of thioarsenate effects on plants and the contribution of thioarsenates to the As load of plants. The proposed project aims at dissecting the uptake pathways for various thioarsenates in plants, the metabolic conversion of thioarsenates through reduction and complex formation within plant cells, the mobility of thioarsenate-derived arsenic species between plant tissues and finally the overall contribution of thioarsenate exposure to the arsenic load of plants. The two studied model systems are rice, which is also the main target organism with respect to food safety, and Arabidopsis thaliana, the plant that has enabled many of the major breakthroughs in understanding arsenic transport and metabolism. Mechanistic insights into the plant-thioarsenate interaction will enable approaches to substantially reduce the accumulation of ubiquitous arsenic in crop plants and thus the chronic poisoning of humans.