Comparative study of the physiological responses, secondary metabolites, and gene expression of medicinal plant Prunella vulgaris L. treated with exogenous methyl jasmonate and salicylic acid

Prunella vulgaris L. is medicinally important due to its treatment of mastitis, thyroid gland malfunctions, and infectious hepatitis in northeastern Asia and Europe. However, little is known about the physiological responses, secondary metabolites, and gene expression of P. vulgaris in response to hormone treatment. In this study, field P. vulgaris was transplanted into pots, the role of methyl jasmonate (MeJA: 1 mM) and salicylic acid (SA: 4 mM) was comparatively evaluated in antioxidant systems, secondary metabolites, and gene expression in P. vulgaris 24 h after treatment. The results indicated that the activities of enzymes (ascorbate peroxidase (APX), peroxidase (POD), superoxide dismutase (SOD), and phenylalanine ammonia-lyase (PAL)) and the contents of glutathione (GSH), soluble protein (SP), hydrogen peroxide (H2O2), total phenols (TP), total flavonoids (TF), rosmarinic acid (RA), and hyperoside (Hyp) increased significantly in response to MeJA treatment. Furthermore, MeJA also effectively enhanced the expression levels of PvPAL, 4-coumaroyl CoA ligase (Pv4CL), coumarate 4-hydroxylase (PvC4H), and tyrosine aminotransferase (PvTAT). The effects of SA on the activities of antioxidant enzymes were less obvious, and inhibiting phenylpropanoid biosynthesis-related gene expression resulted in reduced contents of TP, TF, RA, and Hyp. Therefore, the application of MeJA or SA had remarkable impacts of P. vulgaris, which can improve the antioxidant capacity of P. vulgaris, enhance the stress resistance of plants, and can accumulate secondary metabolites by regulating the content of H2O2. These results clarify the mechanism of P. vulgaris adversity regulation and provide a scientific basis for improving the quality of medicinal plants.