Selenium antagonises the toxic effects of arsenic on mungbean (Phaseolus aureus Roxb.) plants by restricting its uptake and enhancing the antioxidative and detoxification mechanisms

The presence of arsenic (As) in the metal-contaminated soils is toxic for the crops causing their impaired growth and development. Selenium (Se) is also likely to be present along with As in the polluted soils. Se at lower concentration (<1ppm) is reported to be stimulatory but is inhibitory at its higher concentration. Reports about As–Se interaction exist only in lower plants like fern but are fewer in higher plants, especially the crops. In the present study, we tested the interactive effects of As and Se especially with a purpose to test whether Se application was effective in countering the As toxicity. The mungbean plants were raised hydroponically in the presence of (a) arsenic alone (2.5, 5.0, 10μM), (b) selenium alone (2.5, 5.0μM), and (c) arsenic and selenium in combination whilst those without any element acted as controls. The effects of these treatments were assessed on growth, stress injury, oxidative damage along with defence mechanisms. Whilst Se application alone was slightly beneficial for the growth, treatment with As severely inhibited the growth at its 10μM level. The As-treated (10μM) plants supplemented with 5μM Se showed improved growth indicating an antagonistic interaction between the two elements. Se at 2.5μM concentration did not affect the As uptake but at 5μM, it significantly reduced it. Consequently, the Se-treated plants also experienced less damage to membranes, chlorophyll and cellular viability induced by As. The oxidative damage due to As was lowered with Se application, which could be related to elevated levels of enzymatic [superoxide dismutase (SOD), catalase (CAT), ascorbate peroxidase (APO), glutathione reductase (GR)] and non-enzymatic [ascorbic acid (ASC) and glutathione (GSH)] antioxidants. Moreover, the detoxification mechanisms recorded as increase in metallothioneins (MTs), thiols and glutathione-s-transferase (GST) activity were found to be elevated in Se-treated plants. Our observations indicated that Se supplementation at lower concentration might be favourable to improve growth and defence ability against As toxicity in crops such as mungbean though field testing would be required to verify this.