Evidence for molecular antagonistic mechanism between mercury and selenium in rice (Oryza sativa L.): A combined study using 1, 2-dimensional electrophoresis and SR-XRF techniques

Mercury (Hg) is a hazardous chemical in the environment and can accumulate in the food chain. Selenium (Se) is a necessary element for human health and has antagonistic effects on Hg toxicity. In this work, we investigated the effect of Se on Hg containing and Hg-responsive proteins in rice using 1, 2-dimensional electrophoresis combined with SR-XRF techniques. Two weeks old rice seedlings were exposed to Hg and/or Se compounds. After 21 days proteins in the rice roots were separated by electrophoresis and their metal contents were determined by X-ray fluorescence to identify Hg and Se responsive biomolecules. The results show that under Hg stress alone Hg is bound to proteins with molecular weights of 15-25 kDa. With the addition of Se, a new Hg-containing protein band in the 55-70 kDa range was also found, while the content of Hg in the 15-25 kDa proteins decreased. Ten and nine new protein spots were identified after adding Se to inorganic Hg and methylmercury exposed roots, respectively. Adding Se regulates the abundance of proteins associated with carbohydrate and energy metabolism, stress response, cell cycle, and DNA replication indicating that these proteins mediate the antagonism of Se against Hg toxicity. This study helps us to better understand the molecular mechanism of Hg tolerance as well as the molecular antagonism between Hg and Se in rice plants.