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Abstract
This study explored the effectiveness of green zinc oxide nanoparticles (ZnO-NPs) foliar spray on tomato growth and oxidative stress relief under drought conditions. Tomato plant subjected to four water regimes (100, 75, 50, and 25% FC), and in the same while seedlings were sprayed with 25, 50, and 100 mg/L green ZnO-NPs. The results showed that tomato growth parameters reduced significantly by increasing drought stress levels, while ZnO-NPs enhanced plant growth under all studied drought levels. Out of three ZnO-NPs concentrations tested, 25 and 50 mg/L ZnO-NPs proved to be the optimum treatments for alleviating drought stress. They increased shoot and root biomass compared to untreated controls. Application of 25 and 50 mg/L ZnO-NPs enhanced shoot dry weight by about 2–2.5-fold, respectively, under severe drought conditions (25%) compared to ZnO-NPs untreated plants. The application of 25 and 50 mg/L green ZnO-NPs decreased the drought-induced oxidative stress as indicated by the reduction in malondialdehyde and hydrogen peroxide concentrations compared to untreated controls. While 100 mg/L ZnO-NPs further increased oxidative stress. The beneficial effects of ZnO-NPs were evident in the plants’ defensive state, in which the concentration of ascorbic acid, free phenols, and the activity of superoxide dismutase, catalase, and ascorbate peroxidase were maintained at higher levels compared to NPs-untreated plants. At severe drought conditions, 25 mg/L ZnO-NPs induced SOD, CAT, and APX activity by about 3.99-, 3.23-, and 2.82-fold of their corresponding controls, respectively. Likewise, at 25% FC, SOD, CAT, and APX activity increased with 50 mg/L ZnO-NPs by about 4.58-, 3.57-, and 3.25-fold consecutively compared with their respective controls. Therefore, foliar use of green ZnO-NPs at lower concentrations might be suggested as an efficient way for enhancing tomato tolerance to drought stress.
Highlights
IntroductionDrought is a major factor affecting the growing and production of crops worldwide [1]
Between the abiotic stresses, drought is a major factor affecting the growing and production of crops worldwide [1]
Tomato shoot and root biomass decreased gradually by increasing drought stress conditions reaching the lowest values at 25% FC (Figure 1)
Summary
Drought is a major factor affecting the growing and production of crops worldwide [1]. Water deficiency induces a set of physiological and biochemical responses in plants and is one of the most complicated adverse conditions, as it depends on the intensity and duration of the stress event and on the stage of plant growth and morphology [2]. Under conditions of severe drought stress, plant cells undergo oxidative damage as a result of the production of reactive oxygen species (ROS). The increase in ROS might adversely damage the cellular organelles, DNA, lipids, and enzymatic configuration and eventually cause cell death [4,5]. Plants have very effective cleaning systems for ROS to protect themselves from destructive oxidative reactions [6]. The antioxidant defense system consists of nonenzymatic antioxidants and some antioxidant enzymes [7]
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