Thymol as a control factor of the expression of key genes of the ginsenoside biosynthesis pathway and its effect on the production of ginseng saponins in Panax quinquefolium hairy root cultures

The cultures of Panax quinquefolium hairy root accumulate ginsenosides, triterpenic saponins, which are attributed numerous pharmacological properties of ginseng such as antioxidant, anti-inflammatory, anti-cancer or regulating nervous, endocrine and cardiovascular systems. The present study is the first one to apply thymol as an elicitor to enhance content of eight ginsenosides: Rb1, Rb2, Rb3, Rc, Rd, Rg1, Rg2 and Re. Additionally the relative expression level of the main regulatory genes (FPS, SS and DS) of the ginsenoside pathway was assessed in studied cultures. To evaluate the functional significance of thymol on FPS, SS and DS expression, quantitative RT-PCR experiments were executed at different time exposure and elicitor concentration. The effect of thymol on ginsenoside production was examined at 0.01, 0.1, 1, 10, 100, 250 and 500 μM concentrations after 24- and 72-h time exposure. The ginsenoside level was determined using HPLC. The maximum yield (express as: content - 20.55 mg g−1 d.w. and productivity - 5.86 mg g−1d.w.L−1day−1) of all the examined ginsenosides was reached in medium containing 1 μM thymol after 72-hour elicitation. The level of all studied saponins increased in non-elicited samples; however, the strongest effect of thymol was observed for metabolites Rg1 and Re (2.73 and 2.56 - fold increase in comparison to control, respectively). Compound Rg2, absent in untreated samples, was detected after stimulation of thymol at concentration > 10 μM.