Impact of nano-TiO2 on salt stress tolerance of Carum copticum

     Soil and water salinity in semi-arid regions such as Iran have been a important threat for plant growth and agriculture. It is demonstrated that TiO2 nanoparticles can improve plant growth and increase stress tolerance in plants. Therefore, in current study, a pot experiment was conducted as factorial with completely randomized design to evaluate the effect of 3 levels of salinity (0, 50, 100 mg/L NaCl) and 5 levels nano- TiO2 (0, 10, 20, 40, 80 mg/L) on ajowan (Carum copticum). Results showed that with increasing salt concentration, fresh and dry weight of roots and shoots, content of chlorophyll a, b and relative water content (RWC) significantly reduced, but content of malon dialdehyde, carotenoids, proline content and the activities of SOD and APX increased in leaves. Foliar spray of nano- TiO2 concentrations influenced all the above mentioned parameters in a dose-dependent manner. Foliar spray with suitable nano- TiO2 concentrations (often 20 and 40mg/L) improved plant growth, content of chlorophyll a, b and carotenoids, RWC, proline accumulation and the activities of SOD and APX and reduced lipid peroxidation level. Impact of 80 mg/L nano- TiO2 on growth parameters and photosynthetic pigments contents was less than 20 and 40 mg/L and significantly increased lipid peroxidation under both normal and salinity stress conditions. In conclusion, it can said that appropriate nano-TiO2 concentrations protected ajowan against salt –induced osmotic- and oxidative stresses through increasing proline accumulation and enhancing the activities of antioxidant enzymes