Arsenic toxicity in plants: Cellular and molecular mechanisms of its transport and metabolism

Arsenic (As), a naturally-occurring metalloid, is not essential for plant growth, but it can accumulate in plants to toxic levels. As a result, it can enter the food chain and pose health risk to humans. Multiple mechanisms are involved in the uptake and metabolism of As in plants. The most toxic forms of this element are As^III and As^V. Methylated As and arsenite (as As^III) move through the noduline 26-like intrinsic protein (NIP) aquaporin channels while arsenate (as As^V) is taken up through the phosphate transporters. In the Pteridaceae family, some fern species show hyper-accumulating behavior towards As in aboveground tissues. However, generally in plants, the chelation phenomenon detoxifies arsenite through complexation with the thiol-rich peptide. This comprehensive review encompasses the mechanisms of transport, metabolism, and tolerance that plants show in response to As. Some recent advancement in plant breeding, genetic modifications and remediation approaches to overcome soil and food contamination problems are also summarized. We will also evaluate the implications of these new findings and assess how this may help in developing the crops that can be grown in high As regions and ultimately will be safe for consumers.