Synergistic role of zinc oxide nanoparticles in enhancing antioxidative defense and drought tolerance via metabolic and essential oil modulation in marjoram

Drought is one significant environmental stress that has a detrimental impact on plant growth and lowers production. This study examined the role of ZnO₂ nanoparticles (NPs) in reducing the harmful effects of drought. The growth features of marjoram plants cultivated in typical and drought-stressed environments (100, 75, and 50% water field capacity) were increased by spraying with solutions containing nanoparticles of ZnO2. In contrast to other treated plants, plants treated with ZnO2 NPs (100 mg L−1) showed greater levels of important osmolytes and conserved more photosynthetic pigments. Furthermore, by raising the membrane stability index, the antioxidant enzymes’ activity, and the levels of lipid peroxidation, hydrogen peroxide, and exogenous application of ZnO2 NPs spraying improved drought tolerance and reduced the membrane injury index. An increase in growth and biochemical parameters, such as total antioxidant activity and anthocyanin content, was detected in ZnO2 NPs-treated drought-stressed marjoram plants. Marjoram plant oil analysis revealed that some components appeared, such as eucalyptol, and others increased, especially in response to treatment with only the lowest water stress (50% WFC) and 100 mg L−1 ZnO2 NPs treatment. Our findings generally corroborated the beneficial effects of applying zinc NPs, particularly the absolute contribution of ZnO2 NPs (100 mg L−1) to lessen drought stress’s negative consequences (specifically, 50% WFC) in marjoram plants.