Innovative strategies for alleviating chromium toxicity in tomato plants using melatonin functionalized zinc oxide nanoparticles

Abstract

This study investigates the biosynthesis, characterization, and application of melatonin-functionalized zinc oxide nanoparticles (ZnO NPs@MT) in alleviating chromium (Cr) toxicity in tomato plants. The biosynthesis of ZnO NPs@MT was achieved using leaf extract from Achillea millefolium. The characteristic properties of ZnO NPs@MT were analyzed using UV–Vis spectroscopy, FESEM, XRD, and HR-TEM. UV–Vis analysis revealed a distinct absorption peak at 366 nm, confirming the formation of pure ZnO NPs@MT with a band gap of 3.39 eV SEM and HR-TEM investigations showed uniformly dispersed rod-shaped particles with an average length of 154 nm and a breadth of 24 nm. XRD patterns confirmed the hexagonal crystallinity of the highly pure ZnO NPs@MT synthesized via the green method. Treatment with ZnO NPs@MT effectively mitigated Cr-induced stress in tomato plants. Cr spiked plants treated with ZnO NPs@MT exhibited a significant increase in root and shoot lengths by 119.5% and 134.7%, respectively. Photosynthetic parameters, including chlorophyll content, CO₂ assimilation rate, and stomatal conductance, improved markedly under Cr stress. Antioxidant enzyme activities were enhanced, bolstering the oxidative stress response. Furthermore, ZnO NPs@MT application reduced electrolyte leakage, malondialdehyde, and hydrogen peroxide levels, indicating decreased cellular damage. Increased concentrations of proline and glycine betaine were also observed, contributing to enhanced stress tolerance. Overall, the application of ZnO NPs@MT demonstrates a promising strategy for improving stress resilience in tomato plants, underscoring their potential in sustainable agricultural practices.