Growth, phytochemical parameters and glycyrrhizin production in licorice (Glycyrrhiza glabra L.) grown in the field with saline water irrigation

Salinity is a worldwide problem in crops that can be managed using salt-tolerant species. Wild licorice (Glycyrrhiza spp.), a genus of the Fabaceae family that is considered medicinal and contains many secondary metabolites, including the triterpenoid glycyrrhizin, can grow in saline conditions. The effects of irrigating five different field-grown genotypes of Glycyrrhiza glabra with two levels of salinity (75/37.5/37.5 and 150/75/75 mM NaCl/CaCl2/MgSO4) have been studied, looking at some plant physiological and biochemical characteristics. Salinity led to decreases in leaf and root biomass and leaf relative water content, increases in leaf antioxidant enzyme activities (peroxidase, superoxide dismutase and polyphenol oxidase), and increases in osmolyte levels (soluble sugars, glycine betaine and proline) in leaves and roots. Salinity caused decreases in root glycyrrhizin concentrations in three of the genotypes and in glycyrrhizin contents in all of them (decreases ranging from 26% to 73% with intense salinity), likely as a result of the large decreases in root biomass. The glycyrrhizin content was only moderately affected by salinity in one of the genotypes (‘Kerman’). In this salinity-tolerant genotype, the expression of some glycyrrhizin biosynthesis genes (bAS, SQS1, SQS2, CYP72A154, CYP88D6 and UGT73) was increased by salinity, but this did not result in increases in glycyrrhizin contents. These results indicate that the genetic background of licorice affects glycyrrhizin contents and its response to salinity stress, and also that one of the genotypes studied can be used by farmers in soils affected by salinity.