The impact of TiO2 nanoparticles treatment, developmental, and environmental factors on phenolic content and antioxidant capacity of grapevine (Vitis vinifera L.) leaves

Abstract

Over the last decades, researchers used several elicitors to increase secondary metabolite synthesis (D'Amelia et al., 2018; Anjum et al., 2019). Several studies are now using a variety of nanoparticles (NPs) as unique and effective secondary metabolite elicitors in planta of several plant species. The most frequent "nano-elicitors" include carbon nanotubes (CNT), silver (Ag), gold (Au), copper (Cu), zinc oxide (ZnO), and titanium dioxide nanoparticles (TiO2 NPs) (Anjum et al., 2019; Khan et al., 2021; Lala, 2021). TiO2 is one of the most popular commercially available nano-size materials that has found application in a variety of fields due to its wide availability, biocompatibility, low cost, non-toxicity, and high chemical stability. In nature, TiO2 exists in four polymorphs: anatase, rutile, brookite, and TiO2 (B). The physical and chemical features of TiO2 depend on the crystal phase, size, and shape of the particles. For example, different phases of crystalline TiO2 have varied band gaps, such as rutile and anatase TiO2, which have 3.0 eV and 3.2 eV, respectively, and these band gaps impact TiO2's photocatalytic activity. The activation of TiO2 NPs by photon energy equal to or more than the TiO2 band gap energy drives an electron from the valence band to the conduction band, leaving a hole in the valence band; electron-hole pairs (the charge carriers) are formed. The electron and hole participate in redox reactions with species adsorbed on the surface of TiO2 such as H2O and O2 to generate reactive oxygen species (ROS). ROS are efficient against pathogens and the degradation of hazardous organic compounds (Kőrösi et al., 2019b). Furthermore, they play a crucial role as signal molecules for upregulating antioxidant defense in plants.