Comparative Analysis of Physiological Impact of γ-Fe₂O₃ Nanoparticles on Dicotyledon and Monocotyledon

Currently, the impact of nanoparticles (NPs) on plants is a provocative and promising field. As well-known, dicotyledon and monocotyledon show significant differences in the structural features of the roots and iron absorption mechanisms, and hence it is very meaningful to carry out the comparative study on the diverse impact of NPs on the physiological behaviors of monocotyledon and dicotyledon. In this study, two typical monocotyledon and dicotyledon crops, watermelon (Citrullus lanatus) and maize (Zea mays L.), were exposed to 0–100 mg/L iron oxide nanoparticles (γ-Fe₂O₃ NPs). The physiological parameters, such as seed germination percentage, root lengths, malonaldehyde (MDA) contents, chlorophyll contents, ferric reductase activity, and iron contents of shoots and roots were determined. Transmission electron microscope (TEM) observations showed that γ-Fe₂O₃ could enter both two plant root epidermis cell, but no translocation of γ-Fe₂O₃ NPs from roots to shoots was found in the two plants. Results showed that 20 mg/L γ-Fe₂O₃ NPs promoted seed germination of watermelon seeds by 14.5% and maize seeds by 10.1%, respectively. And 20 and 50 mg/L γ-Fe₂O₃ NPs could accelerate root elongation of the two plants. Malondialdehyde (MDA) production, an indicator of lipid peroxidation, was no increased by exposure to 20–100 mg/L γ-Fe₂O₃ NPs in watermelon plants, however, 100 mg/L γ-Fe₂O₃ NPs initially induced an antioxidant defense in maize but then the stress was eliminated. 20–100 mg/L γ-Fe₂O₃ NPs could increase the chlorophyll contents of watermelon during the duration of exposure, while chlorophyll contents of maize exposure to γ-Fe₂O₃ NPs were higher than control in the first week but no positive effects were observed in the next two weeks. It’s noteworthy that chlorophyll contents of maize were far higher than that of watermelon in the first week, which might be explained by the higher efficiency of iron uptake in strategy II plants.