Zinc oxide nanoparticles mitigating morpho-physiological changes under drought stress condition

The increasing severity of drought stress poses a major challenge to global crop productivity by impairing plant growth, photosynthesis, and water relations. In this study, zinc oxide nanoparticles (ZnO NPs) were synthesized via an eco-friendly green route using Moringa oleifera leaf extract as a bioreducing and stabilizing agent. The biosynthesized ZnO NPs were characterized by UV–Vis spectroscopy, SEM, and TEM analyses, validating their successful synthesis. Tomato plants (Solanum lycopersicum L. cv. Pusa Ruby) were subjected to drought stress and treated with foliar applications of ZnO NPs at concentrations of 10, 20, 30, 40, and 50 mgL⁻¹ to assess their influence on morphological and physiological traits. Drought stress significantly reduced plant height, leaf area, relative water content (LRWC), and membrane stability index (LMSI), while markedly increasing electrolyte leakage (EL). Foliar application of ZnO NPs effectively mitigated these adverse effects in a dose-dependent manner. The 30–40 mg L⁻¹ ZnO NP treatments showed the most pronounced improvement in growth and stress tolerance parameters. At 40 mg L⁻¹, plant height (91.26 cm), leaf area (139.59 cm²), and MSI (46.31%) were significantly higher compared to drought-stressed, while EL (41.29%) was markedly reduced. Similarly, LRWC (66.89%) improved substantially, indicating enhanced water retention. Overall, green-synthesized ZnO NPs enhanced drought tolerance in tomato by stabilizing cellular membranes, maintaining osmotic balance, and protecting photosynthetic pigments through strengthened defense mechanisms. The optimal concentration of 40 mg L⁻¹ ZnO NPs demonstrated the greatest efficacy, highlighting its potential as a sustainable nanobiofertilizer for improving crop resilience under water-limited conditions.