Synergistic effects of Fe3O4–NPs and Enterobacter cloacae in alleviating mercury stress in wheat (Triticum aestivum L.): Insights into morpho–physio–biochemicals attributes

In the current industrial scenario, mercury (Hg) as a metal is of great importance but poses a major threat to the ecosystem because of its toxicity, but fewer studies have been conducted on its effects and alleviation strategies by using nanoparticles (NPs) and plant growth promoting rhizobacteria (PGPR). Taking into consideration the positive effects of iron oxide (Fe₃O₄)⎯NPs and Enterobacter cloacae rhizobacteria in reducing Hg toxicity in plants, the present study was conducted. A pot experiment was conducted over 60 days using wheat (Triticum aestivum L.) to investigate the effects of varying Hg levels (0, 50 and 100 mg kg^⎯1) combined with different concentrations of Fe₃O₄–NPs (25 and 50 mg L^-1) and E. cloacae (10 and 20 ppm) on various morpho−physio−biochemical responses. The research outcomes indicated that elevated levels of Hg stress in the soil significantly (P < 0.05) decreased plant growth and biomass, photosynthetic pigments, nutrients uptake and gas exchange attributes. However, Hg stress also induced oxidative stress in the plants by increasing malondialdehyde (MDA) and hydrogen peroxide (H₂O₂), which also induced increased compounds of various enzymatic and non-enzymatic antioxidants and also the gene expression and sugar content. Furthermore, a significant (P < 0.05) increase in proline metabolism, the ascorbate-glutathione (AsA–GSH) cycle were observed. Although, the application of Fe₃O₄–NPs and E. cloacae showed a significant (P < 0.05) increase in plant growth and biomass, nutrients uptake, gas exchange characteristics, enzymatic and non-enzymatic compounds, and their gene expression and also decreased oxidative stress. In addition, the application of Fe₃O₄–NPs and E. cloacae enhanced cellular fractionation and decreased the proline metabolism and AsA–GSH cycle in T. aestivum seedlings. Research findings, therefore, suggest that the application of Fe₃O₄–NPs and E. cloacae can ameliorate Hg toxicity in T. aestivum seedlings, resulting in improved plant growth and composition under metal stress, as depicted by balanced antioxidant defense mechanism.