Metabolomics Analyses Revealed the Key Metabolites and Pathways of Panax notoginseng under Heavy Drought Stress

Drought is the most common abiotic stress that hinders plantgrowth. To clarify the changes in the growth and metabolism of Panax notoginseng following drought stress, here the effects of drought stress on the growth and metabolism of P. notoginseng are investigated using gas chromatography-mass spectrometry based on a widely targeted metabolomic approach. We conducted drought stress treatments (DS) and re-watering treatments after drought stress (RW) with no drought stress as the control group. The results showed that DS treatment significantly inhibited biomass accumulation and root development of P. notoginseng. Single saponin Rg1 and total saponin in the roots were the highest in the control group, while the total saponins in the leaves were the highest in DS. A total of 120 metabolites were identified using metabolomics and they were classified into eight categories. The metabolites of P. notoginseng under DS were significantly different from the control and RW treatment. Caffeic acid was significantly enriched in all comparison groups, suggesting its important role in the drought resistance of P. notoginseng. Enrichment analysis of differential metabolites showed that the ATP-binding cassette (ABC) transporters, the metabolic pathway of valine, leucine, and isoleucine were closely associated with the drought resistance of P. notoginseng. We also verified that significantly upregulated differential metabolites such as 5-aminolevulinic acid (5-ALA) and quinic acid can enhance the drought resistance of P. notoginseng through exogenous application.