## 3 Discussion
Elicitation with carvacrol reduced Rb1, Rb3, and Rd levels in studied cultures. A similar effect was noticed after linalool treatment, in relation to saponin Rb1 [33]. The decreased production of some Rb group ginseng was also observed in different phenotypes of _P. ginseng_ hairy root cultures' treatment, depending on the type of applied elicitors [19]. The stimulant influence of carvacrol (at 10-100 uM) was noticed for Rg1, Rg2, and Re saponins. A significant increase in the level of Rg1 and Re ginsengides was noted after _trans_-anethole and methyl jasmonate treatment. Then, the Rg2 metabolite was undetected [30; 34], while the study on _P. quinquefolium_ hairy root cultures, elicited with abscisic acid, demonstrated an increased Rg2 level [31]. The change in individual ginseng contents influences the RbG/RgG parameter. In studied cultures, this parameter was 5.56 in the control samples, and its level was the lowest, 0.59, after carvacrol treatment (72 h of treatment with 100 uM of carvacrol), which implies that the share of protopanaxatriol derivatives significantly increased in the entire pool of determined compounds. These results differed from the ones obtained after the yeast elicitation of _P. quinquefolium_ hairy root cultures [29]. In the transformed root of _P. ginseng_, the ratio of derivatives belonging to Rb-group ginensosides and Rg-group ginensodes ranged between 0.28 and 0.38 in the control and oscillated between 0.4 and 0.81 depending on the phenotype of the hairy roots and the type of elicitor during 72 h of exposure [19]. In addition to content, productivity also indicates that a particular culture can be potentially applied on an industrial scale. An analysis of productivity revealed that its value increased from 3.97 mg\(\cdot\)L\({}^{-1}\cdot\)day\({}^{-1}\) in the control to the maximum, i.e., 5.74 mg\(\cdot\)L\({}^{-1}\cdot\)day\({}^{-1}\), after carvacrol treatment (100 uM of carvacrol and 72 h of elicitation). _P. quinquefolium_ hairy root cultures, growing in shaken flasks and elicited with methyl jasmonate, demonstrated a similar level of productivity. This parameter was, however, lower in comparison to the parameter observed in bioreactor cultures [30]. In the case of adventitious and hairy roots of _P. ginseng_, the productivity values were 1 mg\(\cdot\)g\({}^{-1}\) d.w.\(\cdot\)L\({}^{-1}\cdot\)day\({}^{-1}\) and 1.9 mg\(\cdot\)g\({}^{-1}\) d.w.\(\cdot\)L\({}^{-1}\cdot\)day\({}^{-1}\) (cultures cultured in flasks), respectively [19; 39]. They were significantly lower in comparison to the productivity levels in samples of _P. quinquefolium_ hairy root cultures untreated and treated with carvacrol and described in this paper. An analysis of parameters characterizing the ability of hairy root cultures of _P. quinquefolium_ to produce ginsenoside indicated that carvacrol can affect the biosynthesis of ginseng saponins. Additionally, the obtained results demonstrated that carvacrol can affect the gene expression level. It up-regulated the expression of three genes, _FPS_, _SS_, and _DS_, involved in ginsenoside biosynthesis. The _FPS_ gene codes farnesyl pyrophosphate synthase (FPS). This enzyme performs a pivotal role in the branch point in the MVA pathway (Figure 8). Dimethylallyl pyrophosphate (DMAPP) and 3-isopentenyl pyrophosphate (IPP) are substrates of farnesyl pyrophosphate synthase. DMAPP and two units of IPP undergo a condensation reaction using FPS, which leads to the formation of farnesyl pyrophosphate. These processes include two steps. At first, geranyl diphosphate (GPP) is obtained, and, then, GPP is converted to farnesyl diphosphate (FPS) [40]. Carvacrol contributed to a maximum (70-fold) increase in _FPS_ gene expression in hairy root cultures of _P. quinquefolium_ at a 10 uM concentration and with 12 h of treatment. Similarly, within 12 h a clearly up-regulated _FPS_ gene was observed by [PERSON] et al. [18] in the transformed root culture of _P. ginseng_ elicited with methyl jasmonate. Another investigation showed that MJ treatment enhanced the mRNA level of _P.