ABSTRACT
Heavy metals (HMs) contaminate the soil and pose serious threat to crop production due to their pervasiveness in the environment. The damage posed on plants depends on factors like metal solubility, transport, chemical reactivity and pH of the medium. Among HMs, arsenic is a highly toxic metalloid, which alters the normal physiological and metabolic processes of plants. Because of high solubility and mobility, the inorganic forms (arsenate and arsenite) are more toxic than organic forms. The most extensively investigated factor determining the toxicity of arsenic is the generation of reactive oxygen species (ROS), such as superoxide radical, hydroxyl radical, hydrogen peroxide and singlet oxygen, which lead to oxidative destruction of lipids, proteins and DNA. This damage increases the accumulation of malondialdehyde and hydrogen peroxide, decreases reduced glutathione and causes oxidant-antioxidant imbalance. Detoxification mechanisms evolved by plants to minimize the detrimental effects of ROS involve activation of antioxidative biomarkers. However, under arsenic-stressed conditions, the level of ROS increases and is not completely detoxified by plants. Therefore, additional strategies like the use of silicon, nitric oxide, salicylic acid and selenium are used to combat ROS. This chapter, thus, discusses the generation of arsenic-induced oxidative stress in plants and its possible reversal by scavenging systems.
