Physiological changes of Mentha pulegium in response to exogenous salicylic acid under salinity

Plant productivity could be largely limited by salt stress. Thus, a pot experiment was conducted to evaluate the response of Mentha pulegium to foliar spray of salicylic acid (SA) (0, 0.5, 1 and 1.5 mM) under different salinity levels (0, 25, 50 and 75 mM NaCl). The results revealed that accumulation of malondialdehyde, H2O2, proline, glycine betaine and total phenol as well as the activities of catalase, peroxidase, ascorbate peroxidase, superoxide dismutase and phenylalanine ammonia-lyase were increased with increasing salinity level. However, leaf water content and photosynthetic pigments were significantly decreased by salt stress. SA treatment had no significant effect on glycine betaine, total phenol content and phenylalanine ammonia-lyase activity in saltstressed plants, while this treatment enhanced proline content via increasing pyrroline-5-carboxylate reductase activity and decreasing proline oxidase activity. Foliar spray of SA also stimulated the activities of catalase, ascorbate peroxidase and superoxide dismutase enzymes and thereby limited H2O2 accumulation and lipid peroxidation. Application of 1 and 1.5 mM SA considerably improved leaf water content and chlorophyll content of M. pulegium under different levels of salinity. These results suggest that exogenous application of 1 and 1.5 mM SA could mitigate salt toxicity and improve antioxidant capacity of M. pulegium under different levels of salinity.