Integrated Physiological and Transcriptomic Analyses Reveal Secondary Metabolic Responses of Prunella vulgaris Seedlings to Sodium Nitroprusside Treatment

Prunella vulgaris L. is a valuable edible and medicinal industrial crop widely cultivated and used in Asia and Europe. Although exogenous sodium nitroprusside (SNP, a NO donor) is known to increase the biosynthesis of bioactive polyphenols and triterpenoids in this plant, its precise regulatory network remains unclear. Here, we integrated physiological and transcriptomic analyses to decipher how exogenous sodium nitroprusside (SNP, 100 μM) reprograms secondary metabolism in P. vulgaris seedling leaves at 2, 24, and 48 h post treatment. The results indicated that SNP treatment significantly altered antioxidant and redox responses, elevated osmotic regulators, and increased accumulation of key bioactive compounds (such as rosmarinic acid and ursolic acid), accompanied by increased in vitro antioxidant activity. At 24 h post treatment, our comparative analysis revealed 4341 differentially expressed transcripts (DETs). Exogenous SNP treatment is associated with phytohormone signal transduction, Ca2+ signaling, and secondary metabolite biosynthesis. SNP treatment markedly increased endogenous jasmonic acid (JA) levels and upregulated the expression of core transcription factors (MYBs, bHLHs, WRKYs, and NACs), along with increased expression of JA biosynthesis transcripts (e.g., PvLOXs, PvAOC, and PvACX), as well as key transcripts involved in polyphenol biosynthesis (e.g., PvPAL, PvTAT, and PvRAS) and triterpenoid biosynthesis (e.g., PvHMGS, PvDXS, and PvSQS). Our findings provide a systematic view of the physiological, hormonal, and transcriptional responses through which SNP is associated with changes in secondary metabolism in P. vulgaris and provide a theoretical basis for future studies on foliar SNP application to improve the pharmaceutical quality.