Investigating the impact of TiO2 nanoparticles on bioactive compounds in sweet pepper seedlings: a comparison of foliar and root application methods

Engineered TiO2 nanoparticles (TiO2-NPs) are broadly produced and utilized in various consumer products. However, plant uptake of NPs may lead to disruptions in physiological and metabolic processes, particularly when the plant’s defense mechanisms are overwhelmed. In this study, sweet pepper seedlings were exposed to TiO2-NPs via foliar (2.5% suspension) and root (0.5% suspension) methods, with plants treated with distilled water serving as controls. Results showed that foliar application caused higher accumulation of Ti in leaves as compared to stems, while root exposure led to a higher increase of Ti content in stems than in leaves. Additionally, foliar application led to alterations in chemical composition of the plants, including changes in malondialdehyde (MDA), L-ascorbic acid, total phenolics content, carotenoids, in total antioxidant capacity (TAC) and antioxidant enzymes activity. Root exposure also affected enzyme activity and TAC, but also altered H2O2, MDA and glutathione content. Chlorophylls remained at stable level in the leaves of the seedlings. Overall, these studies provide important information on plant-nanoparticle interactions and the potential effects of different nanoparticle application strategies. These data indicate also that the specific nanoparticles, applied at a controlled manner, have potential to boost the plant metabolism and improve stress tolerance, which is an important factor affecting crops’ quality and productivity.