Exposure to low levels of photocatalytic TiO 2 nanoparticles enhances seed germination and seedling growth of amaranth and cruciferous vegetables

Titanium dioxide (TiO 2 ) is one of the most common compounds on Earth, and it is used in natural forms or engineered bulks or nanoparticles (NPs) with increasing rates. However, the effect of TiO 2 NPs on plants remains controversial. Previous studies demonstrated that TiO 2 NPs are toxic to plants, because the photocatalytic property of TiO 2 produces biohazardous reactive oxygen species. In contrast, another line of evidence suggested that TiO 2 NPs are beneficial to plant growth. To verify this argument, in this study, we used seed germination of amaranth and cruciferous vegetables as a model system. Intriguingly, our data suggested that the controversy was due to the dosage effect. The photocatalytic activity of TiO 2 NPs positively affected seed germination and growth through gibberellins in a plant-tolerable range (0.1 and 0.2 mg/cm 2 ), whereas overdosing (1 mg/cm 2 ) induced tissue damage. Given that plants are the foundations of the ecosystem; these findings are useful for agricultural application, sustainable development and maintenance of healthy environments.