Arsenic Induced Toxicity and Regulation Through Metabolomic, Hormonal and Signaling Hubs in Plants

Arsenic (As) contamination of soil is an alarming problem and, flora and fauna are greatly affected with reduced growth and development. The two forms of inorganic As (iAs), arsenate [As(V)] and arsenite [As(III)], are easily taken up by plant roots through various transporters and are toxic to plants and therefore disrupt major plant metabolic activities. Arsenate mimics phosphate: thus, it can affect cellular signaling by affecting phosphorylation, reduce ATP generation and impact glycolysis and DNA-RNA metabolism. Arsenite is thiol reactive and can form bond with up to three sulfhydryl groups and adversely affect the enzymes containing two or more cysteine residues in close vicinity and dithiol co-factors. Arsenite can also bind to the poly-thiol compounds like phytochelatins, cysteine-rich polymerization product of glutathione. The presence of As induces the production of reactive oxygen species (ROS) and also impacts carbon, amino acid, nitrogen and sulfur metabolisms and source-sink relationships. The defense mechanism of plants counteracts the As stress through morphological and physiological adaptations, which are fine-tuned through a complex network of signaling and effector molecules. The important defense mechanisms include antioxidant enzymes and molecules, and thiol metabolism. The crucial signaling components comprise of nitric oxide (NO), salicylic acid (SA), abscisic acid (ABA), jasmonic acid (JA), microRNAs, mitogen-activated protein kinases (MAPKs), and transcription factors, which coordinate various metabolic processes to improve As stress tolerance of plants. This chapter discusses insights into mechanisms of As stress tolerance and the role of various metabolites and signaling factors in the regulation of As-induced stress events in plants.