The determination of the effects of medium components and elicitor on secondary metabolite production in adventitious root suspension culture of melissa officinalis (Lemon balm)

Adventitious root cultures of plants represent alternative biotechnological methods for the production of bioactive compounds widely used in various sectors, particularly in medicine, pharmacy, cosmetics, and food industries. This study aimed to determine the effects of indole-3-butyric acid (IBA; 0.50, 1.0, 2.0, and 4.0 mg L⁻¹), Murashige and Skoog (MS) medium (0.50, 0.75, 1.0, 1.25, and 1.5 MS), and sucrose concentrations (1%, 2%, 3%, 4%, and 5%) on biomass accumulation, secondary metabolite content (rosmarinic acid, total phenolics, and flavonoids), and antioxidant activity in adventitious root suspension cultures of Melissa officinalis (lemon balm). In addition, based on the findings obtained from the nutrient medium optimization studies, the effects of yeast extract used as an elicitor at different concentrations (50, 100, and 200 μg mL⁻¹) on these parameters were also investigated. Antioxidant activity assays were performed using the DPPH• (2,2-diphenyl-1-picrylhydrazyl) free radical scavenging activity, ABTS•⁺ (2,2′-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid)) cation radical scavenging activity, and FRAP (ferric reducing antioxidant power) methods. The induction of adventitious roots was achieved by culturing the hypocotyl segments of 50-day-old in vitro-grown plants on 1 MS medium supplemented with 1 mg L⁻¹ IBA, 30 g L⁻¹ sucrose, and 2 g L⁻¹ phytagel under dark conditions. For the optimization of medium components (sucrose, MS, and IBA) under suspension culture conditions, 4 g of adventitious roots were cultured in 250 mL Erlenmeyer flasks containing 125 mL of nutrient medium on a shaker at 120 rpm for 30 days. As a result of the study, the optimal concentrations of sucrose, MS, and IBA for fresh weight, rosmarinic acid content, total phenolic compounds, and antioxidant activity (DPPH, FRAP, and ABTS) were determined to be 30 g L⁻¹ (3%), 0.5 MS (2.2 g L⁻¹), and 2 mg L⁻¹, respectively. Under optimized medium conditions, the highest rosmarinic acid content (30.25 ± 0.49 mg g⁻¹ KA), representing a 2.59-fold increase compared to the control group, was observed with the application of 200 μg mL⁻¹ yeast extract. In conclusion, adventitious root cultures of Melissa officinalis represent a promising alternative for the biotechnological production of rosmarinic acid, and the optimization of nutrient medium components along with the application of elicitors plays a crucial role in achieving high-yield metabolite production. Keywords: Adventitious Root, Antioxidant Activity, Elicitor, Melissa officinalis, Rosmarinic Acid, Yeast Extract