In vitro assessment of physiological changes of watermelon (Citrullus lanatus) upon iron oxide nanoparticles exposure

With the rapid development of nanotechnology, developing nano iron fertilizer is an important strategy to alleviate Fe deficiency and elevate Fe fertilization effect in agricultural applications. In this study, watermelon seedlings were grown in soil amended with iron oxide nanoparticles (γ-Fe2O3 NPs) at different concentrations (0, 20, 50, 100 mg/L). The content of soluble sugar and protein, content of chlorophyll and malondialdehyde (MDA), and activity of antioxidant enzymes of watermelon leaves were determined in five successive weeks to evaluate the physiological changes of watermelon plants after γ-Fe2O3 NPs exposure. Transmission electron microscope (TEM) observations indicated that γ-Fe2O3 NPs could enter root cell of watermelon. Results showed that 20 mg/L γ-Fe2O3 NPs didn't cause any oxidative stress on watermelon and 50 mg/L γ-Fe2O3 NPs could increase soluble sugar, soluble protein and chlorophyll content in the growth of plants. In addition, 50 and 100 mg/L γ-Fe2O3 NPs caused oxidative stress on watermelon leaves, but this NP-induced stress was removed with the growth of watermelon. It is noteworthy that we found γ-Fe2O3 NPs might possess an intrinsic peroxidase-like activity. The variation trend of physiological parameters was correlated with the nutritional requirements of plants. It can be concluded that γ-Fe2O3 NPs at proper concentrations have the ability to improve iron deficiency chlorosis and promote the growth of watermelon plants. To the best of the author's knowledge, this is the first holistic study focusing on the impact of γ-Fe2O3 NPs in long-term experiment of watermelon plants.