Investigation of the effect of selenium on growth, antioxidant capacity and secondary metabolites in Melissa officinalis

Melissa officinalis is a plant of Lamiaceae family with medicinal properties which is important for its aromatic, synthetic, and secondary metabolites. The aim of this research was to study the effect of selenium on secondary metabolites and antioxidant properties of Melissa officinalis. For this purpose, an experiment was done in a completely randomized design with four replications. The plants were treated with selenium (0, 0.2., and 5 µM). The experimental factors included root and shoot fresh and dry weights, protein contents, ascorbic acid, enzymes (catalase, ascorbate peroxidase, and superoxide dismutase), peroxide hydrogen, caryophyllene, and caryophyllene oxide. Results showed that application of selenium had positive effects on the wet weight of shoots and roots, dried weight of roots, and ascorbic acid, protein, enzyme (catalase, ascorbate peroxidase), peroxide hydrogen, caryophyllene, and caryophyllene oxide contents of the plants under study (p≤0.05). Also, high concentration of selenium (5 µM) lead to increased z-citral, citral, and geranyl acetate contents of Melissa officinalis essential oils while caryophyllene oxide content increased as a result of low concentration (0.2 µM). Therefore, application of selenium is concluded to play an effective role in increasing secondary metabolites in Melissa officinalis. In general, the study suggests that low concentration of selenium increases the growth of Melissa officinalis plants and improves their growth factors and morphology.