Physiological Mechanism of Salicylic Acid in Mentha pulegium L. under salinity and drought stress

Water stress and salinity are the most common abiotic environmental factors that influenced the biochemical and physiological traits of the plants. The goal of the research was to determine the effects of salt stress and drought stress on physiological and biochemical responses in Mentha pulegium L. and was to evaluate possible effect of exogenous salicylic acid (SA) in amelioration of stress deleterious effects in this plant. Plants were treated with different levels of NaCl (0, 50, 100 and 150 mM) and polyethylene glycol (0, 5, 10 and 15%), and SA (0.5 mM) was applied as a foliar spray. Stressed plants showed a reduction in plant growth and the content of photosynthetic pigments and relative water content (RWC), as well as in the activity of peroxidase (POX) as compared to control plants. Reducing growth in M. pulegium under drought stress was more than salt stress, which showed the higher sensitivity of this plant to drought stress. On the other side, salinity and drought boosted lipid peroxidation, hydrogen peroxide content, proline content and superoxide dismutase (SOD) and polyphenol oxidase (PPO) activities. SA application improved the growth under both stresses, and positive effects of SA in salinity-treated plants were more prominent than drought-exposed plants. SA increased RWC, proline accumulation, antioxidant enzymes activities (SOD, POX and PPO) in plants under salinity and drought conditions. This study further confirms that the application of SA to M. pulegium plants proved very effective to ameliorate the salinity and drought damage.