Trichoderma-Synthesized Iron Oxide Nanoparticles Confer Vanadium Tolerance in Rice Through Multiple Defense Responses

Vanadium (V) toxicity severely restricts plant growth and yield. The mechanistic basis by which Trichoderma-synthesized iron oxide nanoparticles (nFe) can improve V stress tolerance in rice remains unclear. To bridge this gap, we evaluated the protective efficacy of nFe in rice seedlings exposed to vanadium (V) stress. Results revealed that nFe lowered V-induced toxic impacts by minimizing V, MDA, H2O2, and O2•− accumulation in leaves and roots. These reductions were correlated to improved photosynthesis phenomics, biomass, and membrane integrity, and reduced oxidative stress. Furthermore, nFe significantly increased the antioxidant enzyme activity and their gene expressions, and partially restored the amino acid (such as glycine, GABA, and proline) accumulation in V-treated seedlings, underscoring its crucial roles in plant defense. Additionally, nFe modulated the subcellular distribution of V by facilitating cell wall fixation and vacuolar sequestration by regulating chelator genes (OsPCS1, OsMT2b, OsPCS2 and OsGSH). Moreover, nFe recovered V-inducede cellular damages by preserving mesophyll structures, mainly chloroplast and thylakoids membrane. V accumulation, Fe uptake, photosynthesis, redox homeostasis and amino acid metabolism serve as key physiological indicators for evaluating crop cultivation under V-stressed conditions. Practically, the foliar application of biogenic nFe offers a promising and sustainable agricultural strategy to improve crop resilience and ensure food security in metal-contaminated soils.