Melatonin-mediated Elicitation in TDZ Induced Callus Cultures of Echinacea purpurea

Abstract

Echinacea purpurea (L.) Moench, is an important medicinal herb of the Asteraceae family. The plant is highly enriched with antioxidant and anti-inflammatory compounds, greatly benefiting the pharmaceutical industries. The in vitro cultures enable the efficient and sustainable production of plant metabolites that is usually enhanced by the addition of elicitor in culture medium. In the current study, TDZ was efficiently employed for the optimum induction of E. purpurea callus cultures. Furthermore, the impact of varying doses of melatonin on biomass accumulation, antioxidant potential, and secondary metabolites production was assessed in callus cultures of E. purpurea. Among all the tested concentrations of TDZ and inoculated explants, stem-derived callus developed using 3 mg/L TDZ showed 100% callus induction frequency and maximum biomass accumulation (FW: 222.08 g/L, DW: 21.625 g/L). This callus of friable nature was used in further experiments because of the fast proliferation of the segregated cells. Exposing the established callus culture with varying concentrations of melatonin showed promising results. The maximum biomass accumulation (FW: 208.62 g/L, DW: 11.87 g/L), maximum total phenolic production (TPP: 132.8 mg GAE/L) and total flavonoid production (TFP: 585.9 mg QE/L) was observed in callus treated with 25μM melatonin. The optimal DPPH radical scavenging activity (DPPH-FRSA: 92.7%), and total antioxidant capacity (TAC: 63.2 ug AAE /mg) was also recorded in callus maintained at 25μM melatonin. A positive correlation was found between these parameters and biomass. HPLC analysis further revealed the maximum synthesis of majority of compounds at this concentration. However, a peak production of amino acids was observed at lowest concentration of melatonin (1 μM). Our research contributes to a better understanding of TDZ as an effective plant growth regulator having a potential for callus induction and biomass accumulation. The outcomes of this study revealed that elicitation with melatonin might prove to be an effective strategy for increasing biomass, phenolic compounds, flavonoids, and antioxidant potential in E. purpurea callus cultures. Keywords: E. purpurea; Melatonin; Elicitation, Thidiazuron; Callus Cultures; Phytochemicals