An investigation of changes in antioxidant enzymes activities and secondary metabolites of thyme (Thymus vulgaris) seedlings under in vitro salt stress

Salinity is one of the major factors limiting the growth of plants that threaten the sustainability of agriculture in vast areas of the world. It seems that the evaluation of medicinal plants such as thyme due to food, pharmaceutical and health is essential under salinity stress to discover its benefits of economic and health. This study was designed to investigate the effect of salinity on physiological parameters, biochemical and secondary metabolites in thyme (Thymus vulgaris) under in vitro culture conditions. Thyme seedlings grown from the seeds, 4 weeks after growth at 16 hours of light and 8 hours of dark and at temperature of 25±1 ºC in the growth chamber, were transferred to MS (Murashige and skoog) medium containing different concentrations of NaCl (0, 80, 100, 120 and 150 mM) and 25 days after the subculture, physiological parameters such as antioxidant enzymes activities and active pharmaceutical ingredients were measured. 25 days after salt treatment, the chlorophyll a, b, total chlorophyll, carotenoids, and total soluble protein content were significantly decreased with increasing NaCl concentration, whereas increasing the salt concentration increased carbohydrates, proline and phenolics in thyme seedlings. Also salinity led to a significant increase in the activity of antioxidant enzymes. GC-Mass analysis showed that the productions of secondary metabolites were greatly affected by salinity. By increasing salinity level of P-cymene and Gama Terpinene increased and Thymol decreased. In general, it was observed that salinity with changes the physiological and biochemical parameters and the amount of active ingredients of Thyme can change the value of its medicinal properties.