Transport, toxicity and metabolism of dimethylmonothioarsenate (DMMTA) in Oryza sativa and other plant species

• Applicants: Professor Dr. Stephan Clemens; Professorin Dr. Britta Planer-Friedrich (†)
• Subject Area: Plant Physiology
• Term: since 2024
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 549251987

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. Furthermore, it is mobile within the plant and reaches edible organs such as the seeds. 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. Rhizosphere bacteria can methylate arsenic and the respective organic arsenic species are taken up by plants, too. The main inorganic as species generally considered to account for most of the problematic As accumulation in plants is arsenite while organic arsenic species like dimethylarsenate (DMA) are seen as much less threatening. Our studies in the past few years, however, have revealed that sulfur-containing (thiolated) arsenic species occur in rice paddy soils as well. Among them is dimethylmonothioarsenate (DMMTA), which is more toxic to human and other mammalian cells than even arsenite. Moreover, DMMTA can be taken up by plants and transported into the grain. Also, it can form within the plant via thiolation of DMA. Potentially highly problematic for food safety, DMMTA in rice grains escapes detection by established analytical techniques. Since most countries around the world regulate only inorganic arsenic, the particularly toxic DMMTA is not controlled at all. Our project aims at elucidating the mechanisms of DMMTA transport, toxicity and metabolism. 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. A detailed understanding of how DMMTA and other thioarsenates interact with plants will hopefully contribute to substantially reducing chronic human exposure to arsenic.

• DFG Programme: Research Grants