Comparative effects of salt stress on growth and antioxidative responses in different organs of pennyroyal (Mentha pulegium L.)

Pennyroyal (Mentha pulegium L.) is a medicinal plant of the Labiatae family. In this study, it was investigated the effect of salinity on leaf area, shoot length, root length, activities of superoxide dismutase (SOD), peroxidase (POD), polyphenol oxidase (PPO), catalase (CAT), and ascorbate peroxidase (APX) in pennyroyal species. Seeds were sown in Tref peat in greenhouse conditions with 16 h light/ 8 h dark period per 24 h and day/ night temperatures of 25/ 18 ˚C. Then, 60 days seedlings transferred to pots containing perlite and grew in hoagland solution with different concentrations of 0, 25, 50, and 75 mM NaCl. Seedlings were harvested for physiological and biochemical analyzes, after four different harvest times (10, 20, 30, and 40 days). The results showed that leaf area and shoot length decreased with increasing salinity levels, whereas root length increased to 50 mM NaCl and then decreased. Delay in harvest time caused more decrease in leaf area and shoot length. With increasing NaCl, activity of all the enzymes significantly increased at four harvest times. Activities of SOD, PPO, and APX were higher in root than that of leaf and shoot, whereas CAT activity was higher in leaf. On the basis of the obtained data, it can be concluded that pennyroyal reduced negative effects of salinity stress with increasing activities of antioxidant enzymes in leaf, shoot, and root. Antioxidative response of M pulegium has a direct relationship to salt stress time duration.