Impact of external calcium and calcium sensors on ginsenoside Rb1 biosynthesis by Panax notoginseng cells

Abstract The effects of external calcium concentrations on biosynthesis of ginsenoside Rb 1 and several calcium signal sensors were quantitatively investigated in suspension cultures of Panax notoginseng cells. It was observed that the synthesis of intracellular ginsenoside Rb 1 in 3‐day incubation was dependent on the medium Ca 2+ concentration (0–13 mM). At an optimal Ca 2+ concentration of 8 mM, a maximal ginsenoside Rb 1 content of 1.88 ± 0.03 mg g −1 dry weight was reached, which was about 60% and 25% higher than that at Ca 2+ concentrations of 0 and 3 mM, respectively. Ca 2+ feeding experiments confirmed the Ca 2+ concentration‐dependent Rb 1 biosynthesis. In order to understand the mechanism of the signal transduction from external Ca 2+ to ginsenoside biosynthesis, the intracellular content of calcium and calmodulin (CaM), activities of calcium/calmodulin‐dependent NAD kinase (CCDNK) and calcium‐dependent protein kinase (CDPK), and activity of a new biosynthetic enzyme of ginsenoside Rb 1 , i.e., UDPG:ginsenoside Rd glucosyltransferase (UGRdGT), in the cultured cells were all analyzed. The intracellular calcium content and CCDNK activity were increased with an increase of external Ca 2+ concentration within 0–13 mM. In contrast, the CaM content and activities of CDPK and UGRdGT reached their highest levels at 8 mM of initial Ca 2+ concentration, which was also optimal to the ginsenoside Rb 1 synthesis. A similar Ca 2+ concentration‐dependency of the intracellular contents of calcium and CaM and activities of CCDNK, CDPK, and UGRdGT was confirmed in Ca 2+ feeding experiments. Finally, a possible model on the effect of external calcium on ginsenoside Rb 1 biosynthesis via the signal transduction pathway of CaM, CDPK, and UGRdGT is proposed. Regulation of external Ca 2+ concentration is considered a useful strategy for manipulating ginsenoside Rb 1 biosynthesis by P. notoginseng cells. © 2004 Wiley Periodicals, Inc.