Physiological evaluation of drought stress tolerance and recovery in Verbascum sinuatum plants treated with methyl jasmonate, salicylic acid and titanium dioxide nanoparticles

The genus Verbascum L. (Scrophulariaceae) includes medicinal plants, which have several bioactive compounds especially saponins. The possible recovery ability of Verbascum sinuatum from drought stress conditions was assessed by using salicylic acid (SA), methyl jasmonate (MJA) and titanium dioxide nanoparticles (TiO(2)NPs) as plant growth regulators (PGRs) in liquid culture media. Thirty days-old plants were exposed to different concentrations of polyethylene glycol (PEG-6000) for creating artificial drought conditions (0, -0.3, and -0.6 MPa osmotic potential) and also treated with 200 mu M methyl jasmonate (MJA), 100 mu M salicylic acid (SA) and 20 ppm TiO2 nanoparticles (TiO(2)NPs). Results showed that the growth parameters and the content of photosynthetic pigments decreased at higher drought level (-0.6 MPa). However, SA and TiO(2)NPs alleviated the adverse effects of drought stress by increasing water stress tolerance through promotion of enzymatic and nonenzymatic antioxidant defense systems. MJA negatively affected the growth parameters and increased the content of malondialdehyde (MDA), hydrogen peroxide (H2O2) and total saponin and also the activity of peroxidase (POD) and polyphenol oxidase (PPO). Based on the results obtained from this study, the recovery treatments mainly affected the defense-related metabolism in Verbasum sinuatum plants.