Selenium-Mediated Regulation of Antioxidant Defense System and Improved Heavy Metals Tolerance in Plants

Being stalkless organism, agricultural crops are constantly confronted by environmental stresses such as heavy metals (HMs) which severely affect the growth, productivity and thus yield losses. To minimize the HMs-induced phytotoxic effects and improve the HM tolerance by plants, the utilization of beneficial elements such as selenium (Se) as antioxidant defense agent can be effective solutions. At low concentrations, Se compounds (selenite or selenate) can promote plant growth and stress tolerance. The key mechanism is that lower Se doses can activate the antioxidant defense capacity (by stimulating the activities of enzymatic or nonenzymatic antioxidants); reduce the extra accumulation of reactive oxygen species, malondialdehyde (stress marker); and scavenge associated damages due to oxidative stress as well as membrane lipid peroxidation, ultimately enhancing the plant tolerance against HMs stress. Here, we have overviewed the available literature concerning the physiological roles of Se species via the involvement of enzymatic or nonenzymatic antioxidant systems in the alleviation of HMs-induced toxic effects in plants. The aim of the present chapter is to apprise our understandings regarding the beneficial and protective roles of inorganic Se forms (selenite and selenate) on the mitigation of HM stress (via involving antioxidant defense systems) in different plants. In this way, the exploitation of Se as antioxidative agent in HMs-susceptible crops can be ideal strategy to ameliorate HMs stress and Se-exposed plants can display improved growth under environmental stress conditions. Hence, Se-supplementation should be focused to develop stress-tolerant genotypes.