Effects of nanoTiO₂ on tomato plants under different irradiances

In this study, we investigated the physiological and photochemical influences of nanoTiO₂ exposure on tomato plants (Lycopersicum esculentum Mill.). Tomato plants were exposed to 100 mg L^-1 of nanoTiO₂ for 90 days in a hydroponic system. Light irradiances of 135 and 550 μmol_photon m^-2 s^-1 were applied as environmental stressors that could affect uptake of nanoTiO₂. To quantify nanoTiO₂ accumulation in plant bodies and roots, we used transmission electron microscopy, energy-dispersive X-ray spectroscopy, inductively coupled plasma mass spectrometry, and X-ray powder diffraction. Phenotypic and physiological influences such as color change, growth rate, fruit productivity, pigment concentration, and enzyme activity (SOD, CAT, APX) were monitored. We observed numerous effects caused by high irradiance and nanoTiO₂ exposure, such as rapid chlorophyll decrease, increased anthocyanin and carotenoid concentrations, high enzymatic activity, and an approximately eight-fold increase in fruit production. Moreover, light absorption in the nanoTiO₂-treated tomato plants, as measured by a ultraviolet-visible light spectrometer, increased by a factor of approximately 19, likely due to natural pigments that worked as sensitizers, and this resulted in an ∼120% increase in photochemical activities on A, ФPSII, ФCO₂, g_sw, and E.