In vitro proliferation and triterpenoid characteristics of licorice (Glycyrrhiza uralensis Fischer, Leguminosae) stolons

Abstract

Dried roots and stolons of licorice plants (Glycyrrhiza uralensis) are among the most important drugs (Glycyrrhizae radix) in traditional oriental medicine; they are also important commercial products used worldwide in sweetening and flavoring. Here, we describe the establishment of an in vitro stolon culture system for G. uralensis. Stolon formation was induced in single node stems (with axillary buds) grown in Murashige and Skoog (MS) liquid culture medium, supplemented with 0.01 μM α-naphthaleneacetic acid (NAA). Stolons were cultured at 26°C in the dark on a rotary shaker, gyrating at 100 rpm. The same NAA concentration produced the highest rates of stolon proliferation (6.58-fold in 4 weeks). A 6% sucrose concentration also enhanced stolon proliferation (6.34-fold in 4 weeks). GC/MS analysis confirmed the accumulation of small amounts of glycyrrhizin (14 μg g⁻¹ dry weight) in cultured stolons. Interestingly, betulinic acid and oleanoic acid production in vitro were higher than in field-grown stolons. Adventitious root and shoot regeneration from cultured stolons were readily achieved under illuminated conditions in MS medium containing 0.01 μM of NAA and 0.2% gerlite. Regenerated plants produced glycyrrhizin (7,600 μg g⁻¹ dry weight) in their roots. Our in vitro stolon culture system is suitable for studying glycyrrhizin biosynthesis and for rapid propagation of elite licorice clones.