Essential oil constituents and secondary metabolites of Mentha viridis under tissue culture technique using violet visible light emitting diodes (LEDs)

This study aimed to propagate the valuable medicinal plant Mentha viridis through in vitro culture of nodal segments measuring approximately 1-1.5 cm. Two different types of light-emitting diode (LED) systems were used to apply three different concentrations of two different cytokinins: 6-benzylaminopurine (BAP) and thidiazuron (TDZ) at 0, 1, or 2 mg/L. The LED systems were white as a control and violet, which is a 1:1 ratio of red and blue light. After a 30-day incubation period, the results revealed significant improvements in the survival rate and the number of shoots per explant across the various treatment groups. With MS medium supplemented with 2 mg/L TDZ and illuminated by white and violet LEDs, the highest values were obtained, yielding survival rates of 93.3% and 13.3 shoots per explant, respectively. Moreover, the treatment involving 2 mg/L TDZ under violet LEDs illumination exhibited superior outcomes in terms of leaf count per explant, callus formation, and callus size. Notably, no callus formation was observed in response to BAP treatments. All treatments resulted in a significant increase in antioxidant enzyme activity and the accumulation of various compounds, such as anthocyanin, ascorbic acid, phenols, flavonoids, peroxidase, and polyphenol oxidase, when compared to the control in a broader context, the levels of IAA, kinetin, and zeatin increased, while GA3 and ABA decreased in response to the applied treatments, as compared to the control. Additionally, ten compounds were consistently found in all treatments by GC/MS analysis of the micro-propagated Mentha, with carvone accounting for the highest proportion (43.5%) and being the predominant component. Among all treatments, nodal segments that were exposed to violet LEDs and grown on MS medium supplemented with 1 mg/L TDZ had the highest carvone content.