Comparison of soil addition, foliar spraying, seed soaking, and seed dressing of selenium and silicon nanoparticles effects on cadmium reduction in wheat (Triticum turgidum L.)

Wheat cadmium (Cd) contamination is a critical food security issue worldwide, and selenium (Se) and silicon (Si) are widely reported to reduce Cd accumulation in cereal crops. However, few studies have compared the most effective pathway to reduce Cd accumulation in crops using Se nanoparticles (nano-Se), Si nanoparticles (nano-Si), and their mixtures. Here, we investigated the concentrations of Cd in wheat using four application modes: soil addition, foliar spraying, seed soaking, and seed dressing combined with three different materials. The concentration of Cd in wheat grains can be significantly reduced by 31.30-62.99% and 36.96-51.04% through four applications of nano-Se and soil application and seed soaking of nano-Si, respectively. However, all treatments involving mixtures of nano-Si and nano-Se did not show a reduction in Cd concentration. The applications of both nano-Se and nano-Si can enhance antioxidant enzyme systems and regulate Cd-related gene expression to safeguard wheat tissues from Cd stress. Downregulation of the influx transporter from soil to root (TaNramp5) and from root to shoot (TaLCT1), along with the upregulation of the efflux transporter from cytoplasm to vacuole (TaHMA3), contributed to the nano-Si/nano-Se dependent Cd transport and reduced Cd accumulation in wheat grains. Overall, the application of nano-Se instead of nano-Si, and soil addition rather than foliar spraying, seed soaking, and seed dressing, can be efficiently utilized to reduce grain Cd accumulation from Cd-contaminated soils.