Sulfur Reduces Arsenic Accumulation in Rice Shoot by Enhancing Root Retention and Altering Arsenic Metabolism

Rice can potentially pose serious health risks due to its highly efficient arsenic (As) uptake. Sulfur (S) is not only an essential macronutrient, but it also has the ability to decrease As accumulation. In the present study, a hydroponic experiment was conducted to investigate the mechanisms underlying the effects of S on the As uptake and transport with different S (pre-)treatments and levels. The results showed extra S decreased As content by 20-50% in both S-deficiency and S-normal pre-treated shoots compared with no S supply throughout the treatment; As uptake was significantly reduced by 17% and 62% by 2 mmol L-1 of S, under S-deficiency and S-normal pre-treatments. Moreover, the root-to-shoot translocation of As was inhibited by S addition. Both normal S (S0.2) and sufficient S (S2) significantly reduced As root-to-shoot translocation factors by 7%-46%, which could be explained by elevated levels of thiol compounds (by 15%-280%) and the down-regulation of OsLsi2 expression (e.g., reduced by 71% by S at 2 mmol L-1 with the S-normal pre-treatment). More importantly, S also promoted the biotransformation of As(III) in shoot into less toxic As species; the proportion of As(III) in rice shoots was decreased by 25% by 2 mmol L-1 of S under S normal pre-treatment. Overall, this study implies that S could play an important role in the inhibition of As uptake and the detoxification of As in rice by enhancing root retention (the vacuole sequestration) and altering As assimilation, and the potential application of S in rice production in As-contaminated paddy soil