Selenium alleviates toxicity in Amaranthus hypochondriacus by modulating the synthesis of thiol compounds and the subcellular distribution of cadmium

As a beneficial element, Selenium (Se) reduces toxic cadmium (Cd) absorption in many crops, but the effects of Se on Cd hyperaccumulator plants are unclear. This study examined the effects of Se on Amaranthus hypochondriacus (K472). The results showed that Se increased antioxidant enzyme activities, reduced Cd concentrations and toxicity, restored cell viability, and enhanced photosynthesis; these effects increased the biomass of roots, stems, and leaves by 59.87%, 53.85%, 44.19%, respectively, and these values exceeded the biomass of roots and stems in untreated control plants by 56.69% and 15.37%, respectively. Moreover, Se promoted PC synthesis, stably chelated Cd in the form of PC3 and PC4 and transported PC-Cd to vacuoles. Furthermore, Se protected organelles and reduced Cd migration by increasing Cd levels in cell walls and vacuoles. Interestingly, although the Cd content in K472 was decreased, Se maintained the total extracted Cd concentrations and its remediation efficiency by improving biomass and increased tolerance to Cd by approximately 5 times. The experimental results provide novel insights and methods for mitigating toxicity, promoting growth, and broadening the engineering application scope of K472; these results also provide a theoretical basis for further application of Se in soil with high Cd concentrations.