Phase-Selective Synthesis of Anatase and Rutile TiO Nanocrystals and Their Impacts on Grapevine Leaves: Accumulation of Mineral Nutrients and Triggering the Plant Defense.

Titanium dioxide nanocrystals (TiO NCs), through their photocatalytic activity, are able to generate charge carriers and induce the formation of various reactive oxygen species (ROS) in the presence of O and HO. This special feature makes TiO an important and promising material in several industrial applications. Under appropriate antioxidant balancing, the presence of ROS is crucial in plant growth and development, therefore, the regulated ROS production through the photocatalytic activity of TiO NCs may be also exploited in the agricultural sector. However, the effects of TiO NCs on plants are not fully understood and/or phase-pure TiO NCs are rarely used in plant experiments. In this work, we present a phase-selective synthesis of TiO NCs with anatase and rutile crystal phases. The nanomaterials obtained were characterized by means of X-ray diffraction (XRD), transmission electron microscopy (TEM), diffuse reflectance UV-Vis spectroscopy, and electron paramagnetic resonance spectroscopy (EPR). In field experiments, cv. Cabernet Sauvignon leaves developed under natural sunlight were treated with aqueous dispersions of TiO NCs at concentrations of 0.001, 0.01, 0.1, and 1 /%. The effect of the applied nanocrystals was characterized via leaf photochemistry, mineral nutrient contents, and pyridoxine levels. We found that stress responses of grapevine to anatase and rutile NCs treatments are different, which can be related to the different ROS profiles of the two polymorphs. Our results indicate that TiO NCs may be utilized not only for direct pathogen inactivation but also for eliciting plant defense mechanisms.