Phytohormones producing endophytic fungi Paecilomyceslilacinus modulated metabolic, enzymatic, and non-enzymatic antioxidant systems of Zea mays L. under heavy metal stress

BACKGROUND: The continuous growth of the global population is intensifying the challenge of sustaining future food production. Among the major constraints to agricultural productivity, heavy metal (HM) contamination of soils has emerged as a serious environmental problem that adversely affects crop growth and yield. Environmentally friendly strategies are therefore needed to mitigate HM stress in plants. Endophytic fungi have gained attention for their potential to enhance plant tolerance to abiotic stresses. In this study, the endophytic fungus Paecilomyces lilacinus was evaluated for its ability to produce phytohormones and alleviate lead (Pb) and cobalt (Co) stress in maize (Zea mays L.). RESULTS: Firstly, culture filtrate of P. lilacinus was analyzed for phytohormone production under Pb and Co stress conditions. The fungus produced significant amounts of gibberellic acid (43.01 µg mL⁻¹), salicylic acid (2192.1 µg mL⁻¹), and abscisic acid (35.4 µg mL⁻¹), along with measurable protein content (170.06 µg mL⁻¹) in cobalt contaminated filtrate. Secondly, pot experiments were conducted to evaluate the effect of P. lilacinus inoculation on maize plants grown under different concentrations of Pb and Co. Inoculated plants showed increased endogenous levels of GA₃, SA, and ABA, along with significantly higher chlorophyll content compared to non-inoculated controls. The fungal association also enhanced antioxidant capacity, as indicated by increased 2,2-diphenyl-1-picrylhydrazyl (DPPH) inhibition activity, which reached 90.9% under Pb (90 mg) and 89.1% under Co (90 mg). Similarly, the highest ABTS inhibition activity (96%) was recorded under Pb (90 mg). Moreover, P. lilacinus inoculation significantly increased the activities of different antioxidant enzymes, including catalase, ascorbate acid oxidase, and peroxidase. Enhanced uptake of Pb and Co from the soil was also observed in inoculated maize plants compared with control plants. CONCLUSION: The findings demonstrate that Paecilomyces lilacinus mitigates heavy metal toxicity in maize by enhancing phytohormone production and strengthening antioxidant defense mechanisms in a symbiotic association with the host plant. This endophytic interaction improves plant tolerance to Pb and Co stress and promotes metal uptake, highlighting the potential of P. lilacinus as a sustainable biological approach for reducing heavy metal toxicity and improving crop productivity in contaminated soils.