Effect of drought stress on growth parameters, osmolyte contents, antioxidant enzymes and glycyrrhizin synthesis in licorice (Glycyrrhiza glabra L.) grown in the field

• Published in: Phytochemistry (Oxford) Vol. 156; pp. 124 - 134
• Main Authors: Hosseini, Marjan Sadat, Samsampour, Davood, Ebrahimi, Morteza, Abadía, Javier, Khanahmadi, Morteza
• Format: Journal Article
• Language: English
• Published: England Elsevier Ltd 01.12.2018
• Subjects: Antioxidant enzymes; Drought stress; Fabaceae; Gene expression; Glycyrrhiza glabra; Glycyrrhizin; Reactive oxygen species; Triterpenoid; Glycyrrhizin; Reactive oxygen species; Triterpenoid; Glycyrrhiza glabra; Antioxidant enzymes; Drought stress; Gene expression; Fabaceae
• ISSN: 0031-9422; 1873-3700
• DOI: 10.1016/j.phytochem.2018.08.018

Glycyrrhiza glabra L. (licorice) is a medicinal species rich in the specialised plant metabolite glycyrrhizin. It has been previously proposed that drought, which is increasing in importance due to the climatic change and scarcity of water resources, can promote the synthesis of glycyrrhizin. The effects of slight, moderate and intense drought (70, 35 and 23% of the regular irrigation, respectively) on growth parameters, osmolyte content, oxidative stress markers, antioxidant enzymes, glycyrrhizin biosynthesis genes and root glycyrrhizin concentration and contents, have been assessed in five Iranian licorice genotypes grown in the field. Drought decreased progressively biomass and leaf relative water contents, and increased progressively osmolyte (proline, glycine-betaine and soluble sugars) concentrations in leaves and roots. Drought caused oxidative stress in leaves, as indicated by lipid peroxidation and hydrogen peroxide concentrations, and increased the activities of antioxidant enzymes in leaf extracts (catalase, peroxidase, superoxide dismutase and pholyphenoloxidase). Drought promoted the synthesis of glycyrrhizin, as indicated by the increases in the expression of the glycyrrhizin biosynthesis pathway genes SQS1, SQS2, bAS, CYP88D6, CYP72A154 and UGT73, and increased the root concentrations of glycyrrhizin with drought in some genotypes. However, the large decreases in root biomass caused by drought led to general decreases in the amount of glycyrrhizin per plant with moderate and intense drought, whereas the slight drought treatment led to significant decreases in glycyrrhizin content in only one genotype. Under intense drought two of the genotypes were still capable to maintain half of the control glycyrrhizin yield, whereas in the other three genotypes glycyrrhizin yield was 22–33% of the control values. Results indicate that under intense drought, with only 23% of the normal water dose being applied, an appropriate choice of genotype can still lead to acceptable glycyrrhizin yields. Hypothetical interaction network in response to drought stress in Licorice. The red rectangle includes genes involved in the glycyrrhizin biosynthesis pathway in licorice plants. The expression of genes encoding these enzymes in slight (S), moderate (M) and intense (I) drought stress is shown in the heatmap. Genes are depicted using fold change values and colour coded to reflect changes in relative expression. Each arrow represents the enzyme reactions: FPP, farnesyl pyrophosphate; SQS, squalene synthase; bAS, beta-amyrin synthase; LUS, lupeol synthase; CAS, cycloartenol synthase; CYP88D6 and CYP72A154, cytochrome P450 monooxygenases; UGTs, UDP-glucuronosyltransferases. [Display omitted] •Drought caused progressive decreases in the biomass of five licorice genotypes grown in the field.•Drought caused oxidative stress, and increases in osmolytes and in antioxidant enzymes.•Drought caused increases in the expression of several genes in the glycyrrhizin biosynthesis pathway.•Root glycyrrhizin concentrations only increased in some genotypes under slight/moderate drought.•Glycyrrhizin contents per plant were maintained in four genotypes but only under slight drought.