Carvacrol as a Stimulant 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 accumulation of ginsenosides (triterpenic saponins) was determined in Panax quinquefolium hairy root cultures subjected to an elicitation process using carvacrol at 5, 10, 25, 50, 100, 250, and 500 mu M concentrations during 24 and 72 h exposure. This study was the first one in which carvacrol was applied as an elicitor. The content of eight ginsenosides, Rb1, Rb2, Rb3, Rc, Rd, Rg1, Rg2, and Re, was determined using HPLC analysis. Moreover, the quantitative RT-PCR method was applied to assess the relative expression level of farnesyl diphosphate synthase, squalene synthase, and dammarenediol synthase genes in the studied cultures. The addition of carvacrol (100 mu M) was an effective approach to increase the production of ginsenosides. The highest content and productivity of all detected saponins were, respectively, 20.01 mg center dot g(-1) d.w. and 5.74 mg center dot L-1 center dot day(-1) after 72 h elicitation. The production profile of individual metabolites in P. quinquefolium cultures changed under the influence of carvacrol. The biosynthesis of most examined protopanaxadiol derivatives was reduced under carvacrol treatment. In contrast, the levels of ginsenosides belonging to the Rg group increased. The strongest effect of carvacrol was noticed for Re metabolites, achieving a 7.72-fold increase in comparison to the control. Saponin Rg2, not detected in untreated samples, was accumulated after carvacrol stimulation, reaching its maximum concentration after 72 h exposure to 10 mu M elicitor.