Foliar Application of Nanoparticles Reduced Cadmium Content in Wheat (Triticum aestivum L.) Grains via Long-Distance “Leaf–Root–Microorganism” Regulation

Foliar application of beneficial nanoparticles (NPs) exhibits potential in reducing cadmium (Cd) uptake in crops, necessitating a systematic understanding of their leaf–root–microorganism process for sustainable development of efficient nano-enabled agrochemicals. Herein, wheat grown in Cd-contaminated soil (5.23 mg/kg) was sprayed with different rates of four commonly used NPs, including nano selenium (SeNPs)/silica (SiO 2 NPs)/zinc oxide/manganese dioxide. SeNPs and SiO 2 NPs most effectively reduced the Cd concentration in wheat grains. Compared to the control, Cd concentration in grains was significantly decreased by 35.0 and 33.3% by applying 0.96 mg/plant SeNPs and 2.4 mg/plant SiO 2 NPs, and the grain yield was significantly increased by 33.9% with SeNPs application. Down-regulated gene expression of Cd transport proteins ( TaNramp 5 and TaLCT 1) and up-regulated gene expression of vacuolar Cd fixation proteins ( TaHMA 3 and TaTM 20) were observed with foliar SeNPs and SiO 2 NPs use. SeNPs increased the levels of leaf antioxidant metabolites. Additionally, foliar spray of SeNPs resulted in lower abundances of rhizosphere organic acids and reduced Cd bioavailability in rhizosphere soil, and soil microorganisms related to carbon and nitrogen ( Solirubrobacter and Pedomicrobium ) were promoted. Our findings underscore the potential of the foliar application of SeNPs and SiO 2 NPs as a plant and rhizosphere soil metabolism-regulating approach to reduce Cd accumulation in wheat grains.