## 3 Results
### Biochemical Components of Tea Leaves under Different Concentrations of ZnO-NPs  
The experimental results demonstrated that under different concentrations of ZnO-NPs, the MDA content, POD and SOD activity (Figure 3) in the fresh tea leaves (picked on 1 April) were significantly different. The differences in MDA content and SOD activity in the fresh tea leaves picked on 8 April were highly significant, while the differences in POD activity were not significant. The experimental results showed that the foliar spraying of the ZnO-NPs solution with a concentration of 100 mg\(\cdot\)L\({}^{-1}\) was beneficial to prevent membrane lipid peroxidation of the tea trees. Figure 3A reflects the effect of different ZnO-NPs treatments on the POD activity in fresh leaves of tea plants. Seven days after spraying, POD activity in the fresh leaves differed significantly from one treatment to another, with an 'A' trend. POD activity was the lowest at 0.0162 U\(\cdot\)g\({}^{-1}\cdot\)min\({}^{-1}\) in CK, and then increased with the increasing of the ZnO-NPs concentration, reaching the maximum at 100 mg\(\cdot\)L\({}^{-1}\) (0.034 U\(\cdot\)g\({}^{-1}\cdot\)min\({}^{-1}\)), which was significantly higher than in the other treatments. After that, POD activity started to decrease and reached the lowest at 200 mg\(\cdot\)L\({}^{-1}\) (0.0177 U\(\cdot\)g\({}^{-1}\cdot\)min\({}^{-1}\)), but it was still higher than that of CK. Fourteen days after spraying, the difference in POD activity in the fresh tea  
Figure 3: Effects of zinc oxide nanoparticles on antioxidant enzyme activities (**A**,**B**) and MDA content (**C**) in tea leaves. Different lowercase letters indicated significant differences at the 0.05 level. leaves was not significant, but decreased in a fluctuating manner with the increasing of the ZnO-NPs concentration. POD activity was greater at 10 mg\(\cdot\)L\({}^{-1}\) and 100 mg\(\cdot\)L\({}^{-1}\), which was 0.0371 U\(\cdot\)g\({}^{-1}\cdot\)min\({}^{-1}\) and 0.0287 U\(\cdot\)g\({}^{-1}\cdot\)min\({}^{-1}\), respectively. POD activity in the fresh leaves treated with 150 mg\(\cdot\)L\({}^{-1}\) and 200 mg\(\cdot\)L\({}^{-1}\) of ZnO-NPs was lower than that of CK. Figure 3B describes the impact of different exogenous treatments on SOD activity in the fresh tea leaves. SOD activity in the fresh tea leaves of the CK treatment was higher (0.0346 U\(\cdot\)g\({}^{-1}\cdot\)min\({}^{-1}\)); while it fluctuated with the increase in ZnO-NPs concentration and reached a maximum of 0.0406 U\(\cdot\)g\({}^{-1}\cdot\)min\({}^{-1}\) at 100 mg\(\cdot\)L\({}^{-1}\). The results of SOD activity in tea leaves at fourteen days after spraying were similar to those at seven days after spraying, and the highest SOD activity in the fresh tea leaves was also found under 100 mg\(\cdot\)L\({}^{-1}\) (0.0362 U\(\cdot\)g\({}^{-1}\cdot\)min\({}^{-1}\)), followed by CK (0.0336 U\(\cdot\)g\({}^{-1}\cdot\)min\({}^{-1}\)). SOD activity in the rest of the treatments was lower than that in the CK. As shown in Figure 3C, the trend of MDA content in the fresh tea leaves treated with ZnO-NPs was the same in different sampling periods, and the content varied significantly among these treatments. In the tea samples picked seven days after spraying, MDA content in leaves at 100 mg\(\cdot\)L\({}^{-1}\) was the lowest at 0.267 umol\(\cdot\)g\({}^{-1}\), which was significantly lower than that in the other treatments. The MDA contents in the fresh tea leaves at 150 mg\(\cdot\)L\({}^{-1}\) and 200 mg\(\cdot\)L\({}^{-1}\) concentrations were higher, 3.369 umol\(\cdot\)g\({}^{-1}\) and 3.484 umol\(\cdot\)g\({}^{-1}\), respectively. On 8 April, MDA content in the tea leaves from the CK was 1.355 umol\(\cdot\)g\({}^{-1}\), which was significantly higher than that of the leaves treated with 100 mg\(\cdot\)L\({}^{-1}\) ZnO-NPs, but significantly lower than that of the leaves treated with 150 mg\(\cdot\)L\({}^{-1}\) and 200 mg\(\cdot\)L\({}^{-1}\). MDA content dropped to a minimum value of 0.2724 umol\(\cdot\)g\({}^{-1}\) at 100 mg\(\cdot\)L\({}^{-1}\).