Dynamics of Selenium-Mercury Interaction Under Hg Stress in High and Low Selenium Rice Genotypes

Abstract

Recent studies have demonstrated that selenium (Se) reduces the accumulation of heavy metals in rice tissues. However, the interaction between Se and mercury (Hg) in rice genotypes with high Se content remains to be further investigated. In this study, we used high Se genotypes Z2057B, Z5097B and low Se genotypes Yuenong to explore the dynamics of Se and Hg in various tissues. The results showed that high Se genotypes coupled with low concentration of exogenously applied Se, significantly reduced the uptake of Hg in rice plant. The findings indicated the following order of Hg accumulation: Roots> third leaf > second leaf > first leaf > stem > grains. Observations revealed that both high Se genotypes and Se supplementation significantly restricted the majority of Hg concentration in roots, and minimized its translocation to the aerial parts of the rice plant. In high Se genotypes subjected to mercury stress, MDA accumulation was significantly reduced and SOD antioxidant activity was enhanced in stem and leaves at jointing, booting, heading and maturity stages as compared to low Se genotypes. The application of 1.0mg of Se per kg soil significantly improved the agronomic and physiological characteristics, reduced the Hg contents in aerial parts and increased the Se contents in polished rice grains. Hence, the results lead to the conclusion that (i) cultivating high Se rice genotypes is a viable approach to decrease the Hg accumulation in rice grains, and serves as a crucial strategy to fulfill daily selenium requirements, particularly for populations suffering from selenium deficiency (ii) supplementing ordinary rice with 1-3 mg/kg of selenium can effectively reduce Hg accumulation and improve the grain quality.

Keywords: mercury stress, high selenium rice, selenium-mercury interaction, organic selenium, mercury exposure