Strigolactone could enhances gas-exchange through augmented antioxidant defense system in Salvia nemorosa L. plants subjected to saline conditions stress

•salinity caused the overproduction of reactive oxygen species (ROS) in Salvia nemorosa.•Strigolactone alleviated the negative effects of salinity on gas exchange parameters in Salvia nemorosa.•Strigolactone activated antioxidant defense system in Salvia nemorosa.•Strigolactone resulted in mitigating oxidative stress in Salvia nemorosa.•Strigolactone further increased the essential oil yield of Salvia nemorosa. Salvia is one of the most important herbs that is of universal pharmacological value whose production may be restricted by salt stress. Although the role of phytohormones in modulating the harmful effects of salinity has been investigated, insufficient information has been reported on the positive effects of strigolactone (SL). Therefore, to evaluate the plant reaction to salinity when associated with SL treatments, S. nemorosa were subjected to four levels of salinity (0, 100, 200 and 300 mM NaCl) and five levels of SL (0. 0.1, 0.2, 0.3 and 0.4 μM) under greenhouse conditions. The outcomes demonstrated that salinity reduced the plant growth rate and foliar applied SL significantly prevented salinity stress-induced loss of growth. Increasing salinity significantly reduced leaf chlorophyll content, Fv/Fm and gas exchange parameters and these negative effects could be mitigated by SL application. Providing salt stressed Salvia plants with various levels of SL mostly accompanied with a slow but significant decrease in the activities of peroxidase (POD), catalase (CAT), superoxide dismutase (SOD) and glutathione reductase (GR). When different concentrations of salinity stress were imposed, increasing levels of SL up to 0.3 μM resulted in lower total phenol content and reduced glutathione (GSH) compared with the plants exposed to salinity alone. When plants were subjected to 100 mM NaCl, SL treatment at 0.3 μM indicated the highest essential oil yield (0.4 g plant−1). The modulatory effect of SL treatments in reducing the deleterious effects of NaCl toxicity could be attributed to more proline accumulation and decreased activity of antioxidant enzymes which improved salt tolerance of Salvia nemorosa.