EFFECTS OF UV IRRADIATION ON PLANT GROWTH AND CONCENTRATIONS OF FOUR MEDICINAL INGREDIENTS IN CHINESE LICORICE (GLYCYRRHIZA URALENSIS)

The main root of Chinese licorice (Glycyrrhiza uralensis) is used worldwide as a medicinal material and flavoring agent. This study aimed to determine UV light stress conditions effective for increasing the concentrations of four medicinal ingredients – glycyrrhizic acid (GL), liquiritin (LQ), liquiritigenin (LG), and isoliquiritigenin (ISLG) – and the main root dry weight of Chinese licorice. All UV treatments were compared to exposure to a white fluorescent lamp as a control. For UV treatments, the white fluorescent lamp was supplemented with either UV-A or UV-B fluorescent lamp or a combination of both. Low intensities of UV-A and UV-B were applied for longer treatment periods, while high intensities of UV-A and UV-B were applied for shorter periods. The control was set in each UV treatment for a same period. The dry weights of the main roots as the medicinal part in each UV treatment were not significantly different from the weights of the controls. The concentrations of the four medicinal ingredients in the high intensity UV-B irradiation treatments (BH and AHBH) over 5 or 6 days were 50-70% higher than those in their respective controls. LG and ISLG concentrations in the medium intensity combined UV irradiation treatments (AHBL and ALBH) over 10 days were 140 and 350%, respectively, greater than the levels in their respective controls. These results suggest that UV-B or combined UV-A and UV-B irradiation with white light over 5 to 10 days is more effective than irradiation of white light alone in increasing the contents of GL, LQ, LG, and ISLG in dried main roots without inhibiting the growth of the main root.