Different effects and mechanism of selenium speciation on cadmium uptake by rice (Oryza sativa L.)

Cadmium (Cd) contamination in rice poses a serious threat to global food security and human health. Selenium (Se), as a natural mineral element, plays an important role in mitigating Cd stress in rice and Se deficiency in humans. However, there are fewer studies on whether different forms of Se make a difference in the uptake of Cd by rice, which seriously limits the application of Se in mitigating Cd contamination in rice. In this study, we explored the effects of different concentrations of selenite and selenomethionine (SeMet) on Cd uptake in rice through hydroponic and pot experiments. The results showed that selenite and SeMet significantly inhibited Cd uptake in brown rice and were below the limit of 0.20 mg kg^-1 specified in the GB2762-2022 standard. SeMet was more effective in reducing Cd accumulation in brown rice, at a concentration of 0.50 mg kg^-1, SeMet reduced the Cd concentration in brown rice by 72.53%, which was 1.55 times higher than that of selenite (46.91%). The results showed that increased antioxidant enzyme activity and reduced oxidative damage positively affected the mitigation of rice Cd toxicity. SeMet was more beneficial in reducing the direct migration of Cd from rice roots to brown rice, promoting the complexation of Cd in subcellular soluble fractions of roots, reducing the uptake and translocation of Cd in rice, and promoting the generation of iron films on the root surface of rice during the maturation stage, which forms an effective barrier to the uptake of Cd in rice. Our results provide insights into the mechanisms underlying the differences in the mitigation of rice Cd contamination by different forms of Se and are important for the efficient utilization of Se to improve food safety and human health.