Green synthesized zinc oxide nanoparticles confer drought tolerance in melon (Cucumis melo L.)

Green synthesized nanoparticles present an eco-friendly and cost-effective solution for plant modulation against abiotic stress. The present research aims to explore the role of biogenically synthesized zinc oxide nanoparticles (ZnO.NPs) in mitigating drought-induced alterations in Cucumis melo L. For this experiment, plants were exposed to drought, elicited by polyethylene glycol (10%) and treatments of ZnO.NPs. Treatments were designed as non-stressed seedlings, drought-stressed (DS), and 4 doses of ZnO.NPs (75, 100, 125 and 150mgL-1 ZnO.NPs + DS). Results show that drought exposure caused oxidative damage in melon seedlings, which was reflected from incline in hydrogen peroxide, lipid peroxidation, electrolyte leakage and decline in pigments and osmolytes as well as chloroplast ultrastructural integrity. Furthermore, the photosynthetic functions, vegetative growth and nutrients uptake were significantly compromised. Alternatively, melon seedlings supplemented with ZnO.NPs manifested enhancement in tolerance against drought. ZnO.NPs dosage stimulated the drought tolerance associated genes (SOD, POD, CAT, APX, DREB2D, DREB3), antioxidant activities and improvement in nutrients acquisitions. Moreover, plant photosynthetic functions and pigments content, soluble sugar and protein, vegetative growth and chlorophyll fluorescence showed significant improvement with ZnO.NPs application. The upregulation of genes, antioxidant activities, osmolytes and nutrients acquisition synergistically improved the tolerance of melon seedlings against oxidative damage. Furthermore, the decrease in oxidative damage to melon seedlings was confirmed through chloroplast ultrastructural observation using a transmission electron microscope. Nevertheless, this remarkable change was more notable at optimum concentrations of ZnO.NPs (75 and 100mgL-1). The findings of the current study offer potential contribution in preserving melon crops from oxidative damage induced by drought stress and a step forward into sustainable agriculture