This study is aimed at evaluating the effects of TiO2NPs on biochemical and physiological parameters of marigold (Calendula officinalis L.) under NaCl stress. Treatments included TiO2NPs applied as foliar spraying in three levels (50, 100, and 200 mgL-1), no foliar application as control, and different NaCl levels (0, 30, 60, and 90 mM) by adding NaCl to irrigation water. According to the results, the application of different concentrations of TiO2 had various effects on the studied parameters. The use of 100 mgL-1 TiO2NPs increased flavonoid content of the leaves (at 30 mM NaCl), cell membrane injury (with no salinity), CAT and SOD activities (at 90 mM NaCl), and PPO activity (at 60 mM NaCl). On the other hand, using 100 mgL-1 TiO2NPs under salinity stress decreased MDA and H2O2 contents. Moreover, using 200 mgL-1 TiO2NPs increased photosynthetic pigments content, total flavonoid content of flowers, total soluble sugar, carotenoid content of flowers, and RWC (at the treatment with no salinity), aboveground and underground biomasses (at 30 mM and 60 mM NaCl, respectively), phenolic content and antioxidant activity (at 30 mM NaCl), and APX activity (at 90 mM NaCl). In conclusion, the findings of the present study indicated that TiO2NPs could be a useful material to mitigate the harmful effects of salinity stress. Furthermore, the TiO2NPs spraying could have beneficial effects on osmotic adjustment, biochemical compound, non-enzymatic and enzymatic antioxidant activities, and growth of marigold under NaCl stress conditions.

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