ARSENIC UPTAKE AND ACCUMULATION IN PLANTS: TOXICITY AND ANTIOXIDANT DEFENCE SYSTEM

Arsenic uptake by plants is species-specific and its level in terrestrial plants of uncontaminated sites ranged from 0.009 to 1.5 mg/kg. Plants with high metal or metalloid uptake capability in their biomass are called hyperaccumulators. The most efficient arsenic (As) hyperaccumulator belongs to Pteridaceae with species Pteris vittata L. and Pityrogramma calomelanos L., both species can accumulate more than 8000 mg/kg As in their above-ground parts. Higher concentrations of As can interfere with various metabolic activities and manifest through several morphological impairments. A higher concentration of As accelerates the production of free radicals and reactive oxygen species (ROS) within the cell. Plants have a scavenging system to regulate the production of ROS; the scavenging system is also known as the antioxidant defence system. The defence mechanism consists of both an enzymatic and non-enzymatic antioxidant system. Non-enzymatic antioxidant includes carotenoids, ascorbic acid, and glutathione whereas the enzymatic antioxidant system comprises superoxide dismutase, catalase, ascorbate peroxidase, guaiacol peroxidase, and glutathione reductase