Unraveling Physiological and Metabolomic Responses Involved in Phlox subulata L. Tolerance to Drought Stress

Metabolic responses are important for plant adaptation to abiotic stress. To investigate the responses of Phlox subulata L. to drought stress, we analyzed its physiological and metabolic changes using gas chromatography-mass spectrometer. Based on the physiological indices, P. subulata L. has tolerance to drought to some degree. Our results showed that there were a total of 30 key metabolites induced by drought stress, including amino acids, organic acids, sugars and sugar alcohols, nucleic acid and its derivatives, and other organic compounds. The glutamic acid-mediated proline biosynthesis pathway is continuously upregulated under drought stress, which could regulate osmotic pressure and maintain intracellular environmental stability. More secondary metabolites are used to increase glycolysis and tricarboxylic acid cycle, to accelerate energy production and to enhance the glutamic acid-mediated proline biosynthesis pathway, which are necessary to increase osmotic regulation. Prolonged drought stress induced progressive accumulation of compatible osmolytes, such as proline and inositol, sugars, and amino acids. Therefore, drought caused systemic alterations in metabolic networks involving transamination, TCA cycle, gluconeogenesis/glycolysis, glutamate-mediated proline biosynthesis, shikimate-mediated secondary metabolisms, and the metabolism of pyrimidine. These data suggest that plants may utilize these physiological and metabolomic adjustments as adaptive responses in the early stages of drought stress. These results deepen our understanding of the mechanisms involved in P. subulata L. drought tolerance, which will help improve the understanding of drought’s effects on plant systems.