Microbacterium sp.-Nitric Oxide-Ag-NPs Alleviate Mercury Toxicity in Wheat by regulating Redox Homeostasis and Restricting Hg Uptake and Translocation

Mercury (Hg) contamination impairs crop productivity by disrupting photosynthesis, inducing oxidative stress, and increasing Hg accumulation in plant tissues. Sustainable strategies for mitigating Hg phytotoxicity in agriculturally important crops remain needed. This study evaluated the combined effects of a Hg-tolerant plant growth-promoting rhizobacterium (PGPR), Microbacterium sp. PGPB-3 strain, nitric oxide (NO), and silver nanoparticles (Ag-NPs) on Hg-stressed wheat. Wheat plants exposed to increasing Hg concentrations were treated individually or with combinations of PGPB-3 strain, NO, Ag-NPs, and their growth, photosynthetic performance, oxidative stress, antioxidant defense, and Hg accumulation were assessed. The Hg stress markedly reduced wheat growth, biomass, and photosynthetic efficiency while increasing reactive oxygen species (ROS) accumulation and oxidative damage. Under 25 mg Hg kg^-1 soil, the combined treatment improved root length (33.3%), root biomass (67.5%), carotenoid content (36.7%), and effective quantum yield of photosystem II (ΦPSII; 25%) relative to Hg-stressed plants. Antioxidant enzyme activities were highest under the PGPB-3 + NO + Ag-NPs treatment. This treatment also reduced Hg accumulation by 81% and strongly restricted Hg translocation to shoots, while improving the tolerance index (TI) by 25%. Overall, combined application of Microbacterium sp. PGPB-3, NO, and Ag-NPs alleviates Hg toxicity by enhancing antioxidant defenses, reducing oxidative damage, and restricting Hg uptake and translocation. These findings highlight the potential of an integrated microbial-chemical-nanomaterial approach for improving wheat resilience under Hg stress.