Zinc-based amendments and Zn-solubilizing beneficial bacteria mitigate lead-induced toxicity in chickpea (<i>Cicer arietinum</i> L.).

Abstract

Lead (Pb) is a toxic metal that disrupts plant physiological processes and poses significant human health risks. Fertilizers, nanomaterials, and mineral-solubilizing plant growth-promoting rhizobacteria (PGPR) support phytoremediation as an emerging, eco-friendly strategy for metal detoxification by improving nutrient availability and minimizing metal toxicity in plants. This study explored the interactions of Zn-fertilizer, zinc-oxide nanoparticles (ZnO-NPs), and Zn-solubilizing <i>Enterobacter cloacae</i> (Zns-<i>Ec</i>) in mitigating Pb-induced phytotoxicity in 50, 100, and 150 mgPbkg^-1 soil-stressed chickpea. Under Pb stress. Zn, ZnO-NP and Zns-<i>Ec</i> significantly (<i>p</i> < 0.05) improved root biomass (23.4, 52.3, and 71.4%), chl <i>a</i> (21.2, 26.5, and 39.8%), and carotenoids (26.7, 29.7 and 45.7%) in chickpea subjected to 50 mgPbkg^-1 soil. Zn, ZnO-NP and Zns-<i>Ec</i> interactions reduced lipid peroxidation (LPO), hydrogen peroxide (H₂O₂) and membrane integrity and increased soluble proline, helping to mitigate oxidative stress in Pb-stressed chickpea. Zn, ZnO-NP and Zns-<i>Ec</i> increased antioxidant enzyme activity of chickpea with highest increases in catalase (CAT; 33.4, 40.7 and 51.2%), ascorbate peroxidase (APX; 24.5, 29.8, and 41.2%), glutathione reductase (GR; 20.7, 33.1 and 48.9%), peroxidase (POD; 24.8, 34.5, and 48.9%) under 150 mgPbkg^-1 stress. Treatments of Zn, ZnO-NP and Zns-<i>Ec</i> greatly reduced Pb uptake in roots (20.1, 35.7, and 67%) and shoots (17.6, 29.5 and 54%), in 50 mgPbkg^-1-stressed chickpeas. Additionally, Zn amendments significantly reduced Pb concentrations in rhizosphere soil, increased levels of available K and soluble P. Rhizosphere soil harvested from Zn, ZnO-NPs, and Zns-<i>Ec</i> treatments showed increased available P (8.2 24.5 and 29.5%) and K (24, 21, 34.5%) content under mgPbkg^-1 Pb treatment. Zn, ZnO-NP, and Zns-<i>Ec</i> mitigated Pb toxicity in chickpea by enhancing antioxidant enzyme activity, reducing lipid peroxidation, and limiting Pb uptake through Zn-Pb interaction and rhizosphere immobilization. These findings the synergistic role of Zn amendments and metal-tolerant PGPR in improving plant resilience under heavy metal stress.