## 3 Discussion  
Most reports concerning essential oils (EO) are focused on research related to their chemical profile and biological activities [35]. One of the interesting examples of EO ingredients is carvacrol (2-Methyl-5-[1-methyl ethyl]-phenol). It is a naturally occurring phenolic monoterpenoid and a cynene derivative, present in the essential oils of _Thymus vulgaris_, _Lepidium flavour_, _Origanum scabrum_, _Origanum microphyllum_, _Origanum onites_, and _Origanum vulgare_. In vitro and in vivo studies confirmed pharmacological activities of carvacrol such as antidiabetic action and antioxidant, anti-inflammatory, hepatoprotective, antitumor, neuroprotective, and antimicrobial properties [36; 37]. Bearing in mind that EO compounds demonstrate multidirectional activity and the fact that there are no studies on the application of essential oil ingredients to intensify the accumulation of secondary metabolites in plants, our team started investigating the influence of essential oil components on the biosynthesis of medicinal metabolites in hairy root cultures [33; 34]. This study is a continuation of previous research and the first one on carvacrol application to enhance triterpene saponin production in _P. quinquefolium_-transformed root cultures and carvacrol influence on gene expressions' coding of key enzymes of the ginseng pathway. The obtained results revealed that the maximum total content of the tested saponin was about 20 mg\(\cdot\)g\({}^{-1}\) d.w. (19.75 mg\(\cdot\)g\({}^{-1}\) d.w. and 20.01 mg\(\cdot\)g\({}^{-1}\) d.w., respectively, after 24 and 72 h of elicitation) with 100 uM of carvacrol. This amount was similar to the level observed for all ginsengides after the yeast extract elicitation of _P. quinquefolium_ hairy root cultures [29]. In contrast, methyl jasmonate treatment contributed to a higher total content of ginseng saponin [30]. Transformed root cultures of American ginseng were also elicited with use of linalool and _trans_-anethole [33; 34]. Then, it was also noticed that these ingredients of EO stimulated ginseng accumulation in _P. quinquefolium_ cultures. The optimal concentration and exposure time of essential oil compounds to stimulate secondary metabolite accumulation should be experimentally estimated [33; 34]. Carvacrol, similarly to _trans_-anethole and linalool, improved the total ginseng accumulation after \begin{table}
\begin{tabular}{c c c} \hline \hline
**Ginsenosides** & **Elicitation 24 h** & **Elicitation 72 h** \\ \hline Rg1 & \(-0.25\) & \(-0.06\) \\ \hline Re & 0.72 & 0.04 \\ \hline Rg2 & 0.65 & 0.47 \\ \hline Rb1 & \(-0.91\) & \(-0.57\) \\ \hline Rc & \(-0.83\) & \(-0.59\) \\ \hline Rb2 & \(-0.81\) & \(-0.69\) \\ \hline Rb3 & \(-0.82\) & \(-0.61\) \\ \hline Rd & \(-0.90\) & \(-0.87\) \\ \hline Rg group & 0.79 & 0.08 \\ \hline Rb group & \(-0.87\) & \(-0.74\) \\ \hline Total & 0.09 & \(-0.40\) \\ \hline \hline \end{tabular}
\end{table} 
Table 1: [PERSON]’s rank correlation coefficient between ginseng content/productivity and carvacrol concentration and time of elicitation. short-time elicitation, whereas methyl jasmonate brought about the most intensive biosynthesis of ginseng saponin after 7 days of treatment in these cultures and in hairy root cultures of another species of ginseng--_Panax ginseng_[18; 30; 33; 34]. Moreover, [PERSON] et al. [19] and [PERSON] [38] showed significant differences among the used elicitors in ginseng production in hairy and adventitious root cultures of Korean ginseng, respectively. In addition to the elicitor type, its concentration is also highly important in ensuring a successful elicitation process. The results of this study showed that different concentrations of carvacrol allow for achieving the maximum contents of individual ginseng. A similar observation was noticed after linalool elicitation [33]. In contrast, less varied findings, especially regarding protopanaxadiol derivatives, were obtained in response to the _trans_-anethole and methyl jasmonate treatment of _P. quinquefolium_ hairy root [30; 34].