Arsenic uptake and metabolism in arsenic resistant and nonresistant plant species

Summary Elevation of arsenic levels in soils causes considerable concern with respect to plant uptake and subsequent entry into wildlife and human food chains. Arsenic speciation in the environment is complex, existing in both inorganic and organic forms, with interconversion between species regulated by biotic and abiotic processes. To understand and manage the risks posed by soil arsenic it is essential to know how arsenic is taken up by the roots and metabolized within plants. Some plant species exhibit phenotypic variation in response to arsenic species, which helps us to understand the toxicity of arsenic and the way in which plants have evolved arsenic resistances. This knowledge, for example, could be used produce plant cultivars that are more arsenic resistant or that have reduced arsenic uptake. This review synthesizes current knowledge on arsenic uptake, metabolism and toxicity for arsenic resistant and nonresistant plants, including the recently discovered phenomenon of arsenic hyperaccumulation in certain fern species. The reasons why plants accumulate and metabolize arsenic are considered in an evolutionary context. Contents Summary 29 I. Introduction 30 II. Toxicity of arsenic species to plants 33 III. Arsenic resistance in plants 35 1. Arsenic resistance mechanisms 35 2. Arsenate resistence polymorphism 36 3. Mycorrhizal fungi and arsenic resistance 36 IV. Complexation of arsenic 37 V. Arsenic metabolism 37 VI. Arsenic hyperaccumulation 39 VII. Evolutionary context 40 VIII. Conclusions 40 References 40