Antioxidant capacity and chemical composition of Carum copticum under PEG treatment. Roya Razavizadeh*1 and Mozhdeh Karami2

Drought stress is one of the main non-biological factors limiting the growth and yield of plants in dry and semi-dry regions of the world. Plants are the source of much chemicals derived from secondary metabolism. Carum copticum is a plant from the Apiaceae family with the seeds containing 2-4% the essential oil which are rich in monoterpenes such as thymol and are widely used as an antibacterial agent. This experiment was conducted in order to evaluate the effects of drought stress on physiological parameters and essential oil properties of seedlings and callus of C. copticum. For this purpose, seeds ofC. copticum were cultured in Murashige and Skoog medium containing 0, 2, 4, 6, and 8% PEG. Also,calluses cultured were in MS medium containing 0.25 mg.L-1 2, 4-Dichlorophenoxyacetic acid, and 1 mg.L-1 benzyl amino purine and different levels of PEG. After PEG treatment for 4 weeks, results showed that drought stress decreased chlorophylls and carotenoids contents while it increased anthocyanin, phenolic compounds, protein contents, and CAT and APX activities. Unlike CAT and APX, water deficit induced a significant reduction in superoxide dismutase activity. The content of reducing sugars and proline increased progressively when drought stress increased. Furthermore, PEG changed the essential-oil composition in shoots and calluses. Drought stress increased thymol and p-cymene concentration, though it decreased γ-terpinene. In general, these results showed the high tolerance of C. copticum to drought stress and also revealed positive effects of drought on the antioxidant activities and essential oil composition.