Effect of salt stress on the accumulation of triterpenoid saponins in aseptic cultured Glycyrrhiza uralensis

Glycyrrhizae Radix (licorice) comprises the dried roots and rhizomes of the Glycyrrhiza species and has been used as a medicine and sweetener in Asia and Europe. Because prolonged environmental degradation and overharvesting have significantly reduced the available natural sources of Glycyrrhizae Radix, the development of a cultivation system for this plant is needed. However, the accumulation of secondary metabolites is lower in most cultivated Glycyrrhiza plants compared with that in the wild version. Here, we cultivated G. uralensis under various salinity conditions and determined the effect of salt stress on the accumulation of triterpenoid saponins and ononin (isoflavonoid) using liquid chromatography-mass spectrometry. Treatment with up to 1.2% NaCl did not affect the fresh weight of the G. uralensis seedling roots. Moreover, morphological changes were not observed in samples cultivated under 0.3% and 0.6% NaCl, except for a reduction in the number of leaves compared with that of the control plants. The content of glycyrrhizin, licorice-saponins G2, H2, and B2, in the roots increased concomitantly with increasing salt concentration in the medium. In contrast, soyasaponin Bb in the roots decreased significantly at 1.2% salt concentration, in which the concentration of glycyrrhizin and its analogs was the highest. There was no significant difference in the content of ononin. These results demonstrated that salt stress preferentially enhances the production of glycyrrhizin and licorice-saponins in G. uralensis.