Regulatory effects and mechanism of different selenium species on cadmium accumulation in Triticum aestivum L. (microbial response, gene expression and element accumulation)

Decreasing cadmium (Cd) accumulation in wheat grain is significant for human health. This study compared the effect of soil applied different selenium (Se) species on Cd accumulation in wheat. In Cd-contaminated soil, the applications of inorganic Se species, organic Se species, and selenium nanoparticles (SeNPs) had little effect on physicochemical properties, available Cd content, and Cd fractions in soil, but changed the beta diversity and relative abundance of bacteria at genus level. The application of different Se species reduced Cd concentration in wheat grain, and inorganic Se species had the best effect on reducing Cd, with a decrease of 24.1%-57.0%. Under Cd stress, selenite (Se(IV)) application inhibited the expression of Cd transport-related genes; selenate (Se(VI)) application mainly prompted the expression of gene associated with Cd sequestration in vacuole; and seleno-L-methionine (SeMet) and SeNPs application inhibited the expression of genes related to Cd uptake and transport. Further, Se application alleviated the toxicity of Cd stress on chloroplast. Correlation and stepwise regression equation indicated that different Se species had different crucial part affecting grain Cd accumulation. When Cd was absorbed by plant root, different Se species differentially affected the synergistic effect between nutrient elements and Cd. In all, Se application, especially Se(IV) can be effectively used to reduce grain Cd accumulation.