Seed priming with FeO-SiO nanocomposites simultaneously mitigate Cd and Cr stress in spinach (Spinacia oleracea L.): A way forward for sustainable environmental management.

Seed priming with a composite of iron oxide (FeO) and silicon dioxide (SiO) nanoparticles (NPs) is an innovative technique to mitigate cadmium (Cd) and chromium (Cr) uptake in plants from rooting media. The current study explored the impact of seed priming with varying levels of FeO NPs, SiO NPs, and FeO-SiO nanocomposites on Cd and Cr absorption and phytotoxicity, metal-induced oxidative stress mitigation, growth and biomass yield of spinach (Spinacia oleracea L.). The results showed that seed priming with the optimum level of 100 mg L of FeO-SiO nanocomposites significantly (p ≤ 0.05) increased root dry weight (144 %), shoot dry weight (243 %) and leaf area (34.4 %) compared to the control, primarily by safeguarding plant's photosynthetic machinery, oxidative stress and phytotoxicity of metals. Plants treated with this highest level of FeO-SiO nanocomposites exhibited a substantial increase in photosynthetic and gas exchange indices of spinach plants and enhanced activities of superoxide dismutase (SOD), catalase (CAT), and ascorbate peroxidase (APX) antioxidant enzymes by 45 %, 48 %, and 60 %, respectively. Correspondingly, the relative gene expression levels of SOD, CAT, and APX also rose by 109 %, 181 %, and 137 %, respectively, compared to non-primed plants. This nanocomposite application also boosted the levels of phenolics (28 %), ascorbic acid (68 %), total sugars (129 %), flavonoids (39 %), and anthocyanin (29 %) in spinach leaves, while significantly reducing Cd (34.7 %, 53.4 %) and Cr (20.2 %, 28.8 %) contents in plant roots and shoots, respectively. These findings suggest that seed priming with FeO-SiO nanocomposites effectively mitigated the toxic effects of Cd and Cr, enhancing the growth and biomass yield of spinach in Cd and Cr co-contaminated environments, offering a promising sustainable approach for producing metal-free crops.