Arsenic tolerance mechanisms in plants and potential role of arsenic hyperaccumulating plants for phytoremediation of arsenic-contaminated soil

Abstract

Arsenic (As) is a biological non-essential metalloid toxic to both plants and animals. Sources of As toxicity include both geogenic and anthropogenic. Arsenic accumulation in soil leads to deterioration of physiological properties of soil resulting in reduction of soil fertility and crop yield. Arsenic enters into the food chain either by consumption of As-contaminated water or by intake of plants cultivated in As-contaminated soil as plants accumulate As in different edible parts. Arsenate [As (V)] and arsenite [As (III)] are two inorganic forms of arsenic that are available to plants. They are well known for toxicity symptoms in plants with the former being the most toxic form of arsenic. Arsenic toxicity in plants leads to many morphological and physiological changes like reduction in growth, decrease in number of leaves, decrease in germination rate, plasmolysis of the root cells, demodulation, necrosis of leaf tips, leaf wilting, disruption of cellular membrane structure leading to electrolyte leakage, photosynthesis inhibition, and disruption of cellular energy flow. In response to arsenic toxicity, the plants use various detoxification mechanisms, which include non-enzymatic and enzymatic antioxidant defense mechanisms, hyperaccumulation, and phytochelation synthesis for protection of cells and subcellular systems. Hence, it is necessary to understand the bioavailability of As, its assimilation, metabolism, and toxicity in plants for mitigation of As from the contaminated soil and water. Many plant species including halophytes and glycophytes are potential candidates for mitigating toxic effects of As, thus paving the way for detoxification of the As-contaminated soils through phytoextraction, phytostabilization, and phytoexcretion of As. The chapter presents an overview of significant sources of As contamination, As toxicity and bioavailability, potentiality of various plant species to cope up with arsenic toxicity, and their mechanisms of adaptations to heavy metal stress proving their potential role in phytoextraction, phytostabilization, and phytoexcretion of heavy metal-contaminated saline as well as non-saline soils.