Effects of auxin elicitors on root morphology and glycyrrhizin biosynthesis in Glycyrrhiza glabra L. ecotypes

Glycyrrhiza glabra L. is one of the valuable medicinal plants of the world, whose glycyrrhizin, the most important triterpenoid metabolite in its roots, is widely used in food and modern pharmaceutical industries. To overcome the seed germination problems, the risk of plant extinction due to the indiscriminate root harvesting, and the slow rate of natural biosynthesis of secondary metabolites, it is necessary to study on this plant root tissue culture and use elicitors to increase its glycyrrhizin biosynthesis. In the present study, the seed germination rate of two Iranian licorice ecotypes (Kashmar and Joghtai) and an Iraqi ecotype was investigated at different levels of sulfuric acid pretreatment. In addition, differences between the ecotypes in terms of morphology and root glycyrrhizin content were studied in response to IAA and NAA auxin elicitors with concentrations of 0, 0.5, 1, and 1.5 mg.l-1 in ½ MS medium using root explants. The results showed that all three ecotypes obtained the highest seed germination in the 98% sulfuric acid pretreatment for 40 minutes. The Iraqi ecotype was placed in the statistically best group in terms of all traits except glycyrrhizin content under control and some hormone levels (esp. NAA) conditions. In the Iranian ecotypes, the auxin elicitors application significantly improved the root traits and glycyrrhizin content. Kashmar ecotype produced the thickest roots using 0.5 mg.l-1 of IAA and the highest root dry weight (5.8 and 5.4 mg, respectively) using the medium and high concentrations of NAA and IAA. Joghtai ecotype also produced the heavy roots with 1.5 and 0.5 mg.l-1 of IAA and NAA (100 and 79 mg, respectively). In general, the medium and high concentrations of IAA and NAA (1 and 1.5 mg.l-1) caused the highest glycyrrhizin production (8.82 and 7.83 µg.g-1 DW, respectively) in Kashmar ecotype roots. Therefore, selection of appropriate ecotype and auxin elicitors application can increase in vitro production of biomass and root glycyrrhizin content in G. glabra.