Improving drought tolerance and glycyrrhizin content of licorice plant by EPS-producing cyanobacteria

We evaluated the effects of two selected EPS-producing cyanobacterial strains for microbe-dependent drought tolerance in native licorice plant (Glycyrrhiza glabra) and addressed the mechanisms, which might be improved through these interactions. These bacteria were inoculated on the soils in a form of single strain (Anabaena sphaerica or Nostoc pruniforme) or two strains (Anabaena + Nostoc) in greenhouse conditions. The growth parameters, physiological and metabolical responses among treatments were investigated through assaying the antioxidants and glycyrrhizin contents in the plants grown in both normal condition and moderate water stress condition (FC 50%). The reduction of the ratio of root/shoot in response to drought (FC 50%) was correlated with amount of specific metabolites production, including glycyrrhizic acid (GA), glabridin (GB), liquiritin (LQ) and liquiritigenin (LG), especially in soil treated by Anabaena + Nostoc (P < 0.05). In water-deficient conditions, accumulation of GA in plants treared by Anabaena + Nostoc was boosted by 64% and 69% compared to Anabaena and the control, respectively. Besides, a significant increase in catalase activity (25%) was perceived in this treatment after exposure to drought stress. These results highlight the potential role of enzymatic antioxidants and the increase of GA content in responsing to the drought tolerance in licorice plant. Our findings suggest that using EPS-producing strains of Cyanobacteria is an efficient treatment to improve the drought tolerance in cultivation of medicinal plant in soil of arid and semi-arid regions.