Comparative study of osmotic stresses effects on defense mechanisms and secondary metabolites of seedlings and callus of Carum copticum

Carum copticum L. is a medicinal plant of the Apiaceae family with medicinal properties. In this study, the effects of drought stress on the photosynthetic pigments and essential oils as well as the enzymatic and non-enzymatic mechanisms of the seedlings and callus of C. copticum were investigated within the framework of a controlled experiment under in vitro conditions. For this purpose, the seedlings of C. copticum were cultured in the Murashige and Skoog medium containing three levels (0, 3, and 6%) of either sorbitol or mannitol. Furthermore, its calli were independently cultured in the Murashige and Skoog (MS) medium containing 0.25 mg.L-1 2, 4-dichlorophenoxyacetic acid, 1 mg.L-1 benzyl amino purine, and different levels (0, 3, and 6%) of either sorbitol or mannitol. Both sorbitol and mannitol were found to reduce the photosynthetic pigments and carotenoid contents but increased the anthocyanin and flavonoid contents significantly. However, these effects were significantly more severe in plants submitted to mannitol, as compared to the sorbitol-treated ones. With the exception of the mannitol-treated leaf samples whose phenolic contents decreased with increasing drought concentration in the culture media, the phenolic contents in the other samples increased relative to those in the control samples. The ascorbate peroxidase activity was found to decrease in all the treated samples while the catalase activity greatly increased, particularly in the mannitol-stressed plants. Compared to the control, drought led to a significant increase in superoxide dismutase activity in all the samples treated with 6% sorbitol and in the calli samples treated with 3% mannitol, whereas the seedlings grown under mannitol treatment showed almost no difference with the control plants. In addition, drought stress changed the essential oil compounds of both the seedlings and the calli of C. copticum. Analysis of the essential oil constituents by Gas chromatography–Mass Spectrometry (GC–MS) showed thymol, gamatherpinen, and parasimen to be the main essential oil components which increased in quantity under high stress conditions. These bioactive compounds have many industrial and medicinal applications.