Morphological and Biochemical Response of Potatoes to Exogenous Application of ZnO and SiO2 Nanoparticles in a Water Deficit Environment

A field study was conducted to understand the effectiveness of foliar applications of ZnO-NPs (0, 50, 100 mg L−1) and SiO2-NPs (0, 25, 50 mg L−1) on potato plant growth, morphology, nutrient uptake, oxidative stress, and antioxidative response under drought conditions (i.e., 100% crop evapotranspiration ETc, 75% ETc, and 50% ETc). Results revealed that water deficiency significantly hampered plant growth and biomass production and stimulated oxidative stress in potatoes. However, the exogenous application of ZnO-NPs and SiO2-NPs significantly improved plant growth attributes such as the number of branches, plant height, fresh and dry biomass, leaf area, and leaf area index as compared with untreated plants. The foliar application of ZnO-NPs (i.e., 100 and 50 mg L−1) and SiO2-NPs (50 mg L−1) promoted the mineral ion accumulation in plants grown under water deficiency and thus resulted in higher NPK, Zn2+, Fe2+, and Mn2+ contents. A significant reduction in malondialdehyde (MDA) and hydrogen peroxide (H2O2) was found in plants treated with 100 mg L−1 ZnO followed by 50 mg L−1 SiO2 and 50 mg L−1 ZnO nanoparticles as compared with untreated plants, respectively. Furthermore, the aforesaid treatments resulted in the maximum activity of antioxidant enzymes (i.e., superoxide dismutase SOD, catalase CAT, polyphenol oxidase PPO, and ascorbate peroxidase APX) under water deficit stress. Similarly, the foliar application of ZnO and SiO2 nanoparticles improved nonenzymatic antioxidants such as total flavonoid content (TFC) and total phenolic compounds (TPC) as compared with untreated plants (control). Moreover, plant growth traits were significantly and positively correlated with mineral contents, while they were negatively correlated with MDA and H2O2. ZnO-NPs and SiO2-NPs applications improved biochemical traits, which might lead to enhancements in plant tolerance and improvements in potato growth, productivity, and quality traits under water shortage conditions.