Salinity stress alters ion homeostasis, antioxidant activities and the production of rosmarinic acid, luteolin and apigenin in Dracocephalum kotschyi Boiss

Salt stress affects growth and secondary metabolism in medicinal plants. There is no information about the impacts of salt stress on Dracocephalum kotschyi Boiss. Therefore, in this study, the 60-day old seedlings grown in coco peat and perlite were irrigated with various concentrations of NaCl (0, 25, 50, 75, and 100 mM) in accordance with a randomized complete block design for 3 weeks. The results showed that with increasing salt concentration, Na+ concentration was increased, but Ca2+ and K+ concentrations and fresh and dry weights were decreased in both roots and shoots. Besides, photosynthetic pigments and relative water content declined, whereas proline concentration and electrolyte leakage levels elevated in leaves under salinity stress. The activities of ascorbate peroxidase and guaiacol peroxidase enzymes were enhanced at lower salt concentrations but impaired under higher concentrations of NaCl. High-performance liquid chromatography showed that the contents of rosmarinic acid, luteolin, and apigenin were increased with aggravation of salt stress. The highest total phenolic and flavonoid contents and the rosmarinic acid, luteolin, and apigenin contents were verified at 75 mM NaCl that was concomitant with the most 2,2-diphenylpicrylhydrazyl scavenging activity in the leaves. In contrast, all these attributes decreased under 100 mM NaCl. In conclusion, the results unveiled that D. kotschyi is a moderate salt-tolerant plant and adaptive mechanisms adopted by this plant are including Na+ exclusion in roots, the activation of the antioxidant system, and the alteration of phenolic profile. This study also suggests that mild to moderate salinity can be employed as an elicitor to increasing some pharmaceutical important phenolic compounds in D. kotschyi.