Plant growth promoting bacteria regulate antioxidant synthesis in wheat under chromium stress leading to...

Soil contaminated with heavy metals, especially chromium (Cr), is a major issue worldwide due to rapid industrialization. Cr impairs photosynthesis and metabolic homeostasis, leading to reduction in plant growth and yield. The plant growth-promoting rhizobacterial (PGPR) serve an environment friendly biotechnological approach for remediating metal toxicity through bioaccumulation, chelation and modulation in plant antioxidant systems. The study aimed to investigate the ameliorative role of Bacillus cereus-SJ1 and Bacillus aerius-S1 on biochemical, physiological and yield of wheat (Triticum aestivum L.) varieties (Zincol-2016 and Akbar-2019) grown in 60 mg kg^- 1 chromium stress. The Cr exposure caused a significant reduction in germination percentage (- 54%) and extended mean germination time (+ 53%); the disruption in the electron transport chain and suppression of chlorophyll biosynthesis (- 39%) decreased biomass accumulation. These alterations were associated with elevated dissipation of energy fluxes (Mo, Dio/RC) and significant decline in PSII efficiency (Fv/Fm), indicating impaired thylakoid membrane integrity. PGPR inoculation significantly counteracted the adverse effects posed by Cr toxicity by maintaining chlorophyll-protein complexes, enhancing photochemical quenching, and enhancing redox homeostasis. Moreover, the bacterial inoculation lowered H₂O₂ accumulation (- 44%) and malondialdehyde (MDA) levels (- 24%) through upregulation of antioxidant enzymes, thereby stabilizing the metabolic and photosynthetic process, thus improving growth. The B. cereus and B. aerius inoculation remarkably decreased Cr uptake in roots and leaves, suggesting a detoxification effect mediated by reduced metal bioavailability. These findings demonstrate that these PGPR strains (B. cereus and B. aerius) can enhance Cr tolerance, photosynthetic efficiency and yield potential in wheat leading to sustainable crop production under heavy metal stress.