Widely target metabolomics analysis of the differences in metabolites of licorice under drought stress

Plants have abundant species and extensive distribution. They also have outstanding advantages in terms of nutritional health and functional ecology. Licorice (Glycyrrhiza uralensis Fisch.) is an important plant that is both medicinal and edible. Studying the drought resistance adaptability of licorice's economic organs (roots) and the changes in its metabolites is of great significance for the sustainable utilization of licorice resources. In this study, licorice seedlings were used as materials, and natural drought was maintained at different treatment levels. Soil moisture content was controlled by weighing and replenishing the water, including normal water supply (CK), light stress (LS), moderate stress (MS), and severe stress (SS). We examined the changes in licorice metabolites under different drought stresses, mainly through widely targeted metabolomics techniques. Analysis of licorice root extracts by ultra performance liquid chromatography tandem mass spectrometry (UPLC-MS/MS) resulted in the detection of 831 metabolites. These included 177 flavonoids, 140 lipids, 113 phenolic acids, 70 organic acids, 66 amino acids and derivatives, 53 nucleotides and derivatives, 50 terpenoids, 31 alkaloids, 25 lignans and coumarins, and 7 quinones. A total of 18 differentially expressed metabolites were screened out after different drought treatments compared with CK, including three phenolic acids (2-hydroxy-3-phenylpropionic acid, 3-[(1-carboxyvinyl)oxy]benzoic acid, Methyl 3-(4-hydroxyphenyl)propionate), five flavonoids (kaempferol-3-O-(6''-malonyl)glucoside-7-O-glucoside, 6,7-dihydroxyflavone, rhamnocitrin (7-Methylkaempferol), licoflavone A, licorice glycoside B), three sugars and alcohols (sucrose-6-phosphate, D-fructose, ribulose-5-phosphate), one nucleotide and its derivatives (5-methyl-2'-deoxycytidine), two lipids (LysoPE 22:5, Choline Alfoscerate), three amino acids and their derivatives (L-proline, N-acetyl-L-glutamic acid, N-monomethyl-L-arginine) and one organic acid (N-methyl-4-aminobutyric acid). In conclusion, the results provide valuable information for a better understanding of the molecular mechanism of drought resistance in licorice and also provide useful clues for the development and utilization of licorice resources.