Antioxidant defense and secondary metabolites concentration in hyssop (Hyssopus officinalis L.) plants as affected by salt stress

Salt stress is one of the major limiting factors for plant production, and the quality of medicinal plants is also affected by soil salinity. Hyssop (Hyssopus officinalis L.) plants were cultivated for four weeks in perlite: sand and irrigated with Hoagland nutrient solution containing 0, 50, 100, 150, and 200 mM NaCl. Plants growth was decreased by salt stress while the leaf relative water content was not affected, and the chlorophyll content decreased only by the highest salt concentration (200 mM). Sodium was accumulated at small amounts, indicating a high ability of this species to exclude salt. Soluble sugars and proline were accumulated up to 1.6 and 4.5 fold, respectively. The antioxidant enzymes activity (peroxidase, catalase, ascorbate peroxidase) were increased by the salt treatments, particularly in the leaves. The levels of secondary metabolites (saponins, phenolics, flavonoids, anthocyanins, and iridoids) were all increased under salt stress, and the total antioxidant capacity of alcoholic extract of the leaves and roots was significantly higher in the salt-treated compared with control plants. Our results showed that hyssop is a salt-tolerant species, and the quality of this medicinal plant is improved when grown under saline conditions