Exogenous selenium promotes cadmium reduction and selenium enrichment in rice: Evidence, mechanisms, and perspectives

Cadmium (Cd) accumulation in rice, a global environmental issue, poses a significant threat to human health due to its widespread presence and potential transfer through the food chain. Selenium (Se), an essential micronutrient for humans and plants, can reduce Cd uptake in rice and alleviate Cd-induced toxicity. However, the effects and mechanisms of Se supplementation on rice performance in Cd-contaminated soil remain largely unknown. Here, a global meta-analysis was conducted to evaluate the existing knowledge on the effects and mechanisms by which Se supplementation impacts rice growth and Cd accumulation. The result showed that Se supplementation has a significant positive impact on rice growth in Cd-contaminated soil. Specifically, Se supplementation decreased Cd accumulation in rice roots by 16.3 % (11.8-20.6 %), shoots by 24.6 % (19.9-29.1 %), and grain by 37.3 % (33.4-40.9 %), respectively. The grain Cd reduction was associated with Se dose and soil Cd contamination level but not Se type or application method. Se influences Cd accumulation in rice by regulating the expression of Cd transporter genes (OSLCT1, OSHMA2, and OSHMA3), enhancing Cd sequestration in the cell walls, and reducing Cd bioavailability in the soil. Importantly, Se treatment promoted Se enrichment in rice and alleviated oxidative damage associated with Cd exposure by stimulating photosynthesis and activating antioxidant enzymes. Overall, Se treatment mitigated the health hazard associated with Cd in rice grains, particularly in lightly contaminated soil. These findings reveal that Se supplementation is a promising strategy for simultaneous Cd reduction and Se enrichment in rice.