Physiological and molecular effects of TiO₂ nanoparticle application on UV-A radiation stress responses in Solanum lycopersicum L.

Nanoparticles (NPs) of titanium dioxide (TiO₂) alter photosynthetic and biochemical parameters in Solanum lycopersicum L., possibly due to their photocatalytic properties given by energy absorption in the UV-A range; however, the joint effects TiO₂ NPs and UV-A radiation are not well understood. This work evaluates the combined responses of TiO₂ NPs and UV-A radiation at the physiological and molecular levels in S. lycopersicum. In a split growth chamber, the presence (UV-A +) and absence (UV-A −) of UV-A were combined with 0 (water as a control), and 1000 and 2000 mg L⁻¹ of TiO₂ NPs applied at sowing. At the end of exposure (day 30 after sowing), the photosynthetic performance was determined, and biochemical and molecular parameters were evaluated in leaf tissues. Better photochemical performance in UV-A + than UV-A − in control plants was observed, but these effects decreased in 1000 and 2000 mg TiO₂ L⁻¹, similar to net CO₂ assimilation. A clear increase in photosynthetic pigment levels was recorded under UV-A + compared to UV-A − that was positively correlated with photosynthetic parameters. A concomitant increase in total phenols was observed on adding TiO₂ in UV-A − conditions, while a decreasing trend in lipid peroxidation was observed for the same treatments. There was an increase in psbB gene expression under TiO₂/UV-A + treatments, and a reduced expression of rbcS and rbcL under UV-A −. These results suggest that the reduction in photosynthetic performance on applying high doses of TiO₂ NPs is probably due to biochemical limitation, while UV-A achieves the same result via the photochemical component.