Mechanisms of plant adaptation and tolerance to metal/metalloid toxicity

Abstract

Metal/metalloid (HM) toxicity/stress has become a worldwide menace due to the rising accretions in water, soil, and air which lead to detrimental effects in plants. The general consequences of HM toxicity include oxidative injury which causes polypeptide oxidation, lipid peroxidation, enzyme inactivation, DNA mutilation, and/or alteration of other key components of plant cells. To limit the hazardous effects of HMs and their accumulation, plants have evolved detoxification instruments to preserve physiological accumulations of essential metal ions and to reduce the concentration of non-essential HMs. Such mechanisms are mainly based on compartmentalization and chelation by phytochelatins, amino acids, organic acids, glutathione, metallothioneins, etc. Also, toxicity induced by HM can be compensated by decreasing the uptake of it by reduction/alteration of membrane-bound transporters. In addition, plants can be conferred tolerance by sophisticated antioxidant defense machinery, glyoxalase system, and signal transduction pathways induced by HM. In the last decade, studies on omics have revealed many of the genes or their products that have been implicated in these mechanisms, offering the tools for the improvement of crops. Hence, it became vital to integrate recent understanding of different pathways involved in physiological and biochemical processes of HM-stimulated stress responses and adaptation and tolerance in plants on the basis of findings of current molecular biology research.