In addition to the toxic effects of TiO₂ NPs, discussed in previous chapters, these NPs have been also shown to promote photosynthesis and nitrogen metabolism, resulting in the enhanced growth of spinach. It increases the absorption of light and accelerates the transfer and transformation of the light energy. It was also found that treatment with nano-sized TiO₂ significantly increased the level of antioxidant enzymes, and decreased the ROS accumulation and malonyldialdehyde content in spinach chloroplasts under visible and UV irradiation. TiO₂ NPs also increased the superoxide dismutase activity of germinating soybean, enhanced its antioxidant ability, and promoted seed germination and seedling growth.