Chitosan effects on the elevation of essential oils and antioxidant activity of Carum copticum L. seedlings and callus cultures under in vitro salt stress

Chitosan is a natural nontoxic biopolymer, which is indicated as an aid for reducing oxidative injury caused by salt stress. To explore the potential effects of chitosan on the production of secondary metabolites and antioxidant activity of Carum copticum L., commonly known as Ajwain, seedlings and callus under in vitro salt stress, total phenolics, protein content, antioxidant enzyme activities, and essential oil contents were measured. Two-week-old C. copticum was cultured on MS medium containing 0, 10 and 20 mg L−1 chitosan and 0 and 100 mM NaCl. Calli induced on MS medium supplemented with 4 μM benzyl amino purine and 1 μM 2, 4-dichlorophenoxyacetic acid were cultured on MS medium containing 4 μM BAP, 1 μM 2, 4-D, and different concentrations of chitosan with 100 mM NaCl. The total phenolics, protein content, and antioxidant enzyme activities significantly increased in callus cultures and seedlings under NaCl treatment, except for the root phenolic content. On the other hand, chitosan suppressed phenolic accumulation and antioxidant enzyme activities under NaCl treatment. Furthermore, both NaCl and chitosan enhanced the contents of thymol and p-cymene in seedlings and calli. No significant difference was observed between calli and seedlings. Regarding the effects of chitosan, 20 mg L−1 chitosan found to be most effective on phenol content with increased production of thymol and p-cymene, and it could serve as a favorable excipient for the pharmaceutical industry. These results suggest that plant tissue culture techniques are a promising approach for improving the production of target secondary metabolites through abiotic elicitors supplemented to the medium.