Phytotoxicity of nano-zinc oxide to tomato plant (Solanum lycopersicum L.): Zn uptake, stress enzymes response and influence on non-enzymatic antioxidants in fruits

Abstract

The production of metallic nanoparticles is greatly increasing due to its wide range of applications in agricultural formulations. The present pot experiment investigated the uptake of Zn from nano-zinc oxide (n-ZnO)-amended soil at 300, 600 and 1000 mg n-ZnO/kg concentrations, and its effects on the enzymatic and non-enzymatic antioxidants in tomato tissues and fruits respectively. Results showed that root uptake of Zn increased with increasing n-ZnO concentrations. The enzyme activity showed that n-ZnO, through the generation of H2O2 and induction of oxidative stress, significantly reduced the activity of stress-controlling enzymes (APX and SOD) in the root. Conversely in leaves, despite alteration in chlorophylls in the early growing stage, APX activity was only significant at 1000 mg n-ZnO/kg) while SOD activity was enhanced at all treatments. CAT activity was significantly reduced, unlike in the roots where CAT activity was significantly enhanced. Contents of total phenols, flavonoids, β-carotene and lycopene in fruits were significantly reduced by at least 4.8% while ascorbic acid was promoted at low n-ZnO treatments. In conclusion, the toxic effect of n-ZnO on stress enzymes was prominent in tomato roots, and there was also inhibitory effect on induction of non-enzymatic antioxidants in the tomato fruits.