Foliar Application of Selenium Nanoparticles Reduced Cadmium Accumulation and Alleviated Cd Toxicity in Winter Wheat Grown in Cd-Contaminated Soil

This study investigated the efficacy and mechanisms of foliar-applied selenium nanoparticles (SeNPs) in reducing cadmium (Cd) concentrations and alleviating Cd toxicity in winter wheat grown in Cd-contaminated soil. Pot experiments were conducted to evaluate SeNPs of different particle sizes (50, 100, 200 nm) and concentrations (0.125, 0.25 mmol/L). Foliar SeNPs application achieved the dual objectives of significantly decreasing Cd while increasing selenium (Se) concentrations in wheat grain. High-concentration (0.25 mmol/L) SeNPs treatments were most effective, particularly with a particle size of 100 nm size. Compared with the control, SeNPs significantly reduced grain Cd concentrations by 18.9–70.5% and increased grain Se concentrations by 1.2–27.2 times. Durum wheat exhibited a stronger response than soft wheat. The primary mechanisms included: (1) enhancing antioxidant defense: SeNPs significantly boosted superoxide dismutase (55.2–165.2%) and peroxidase (36.5–182.6%) activities, effectively scavenging reactive oxygen species, reducing oxidative stress markers malondialdehyde (12.0–35.1%) and regulating hydrogen peroxide (7.9–64.1%), which mitigated membrane lipid peroxidation. (2) Regulating subcellular Cd distribution: SeNPs increased the proportion of Cd immobilized in the cell wall by 2.9–39.6% and decreased Cd in organelles by 9.1–38.4%, thereby reducing its bioavailability and toxicity. This study provides a theoretical basis for using foliar SeNPs to remediate Cd pollution and simultaneously produce Se-enriched functional wheat.