Spatial Metabolomics Reveals Tissue Specificity and Distribution of Metabolites in Paeonia lactiflora Roots

Abstract Various secondary metabolites accumulate in the roots of Paeonia lactiflora Pall. (P. lactiflora) and exhibit therapeutic potential for multiple disorders. However, their enrichment sites in different tissues or parts of the roots remain unclear. In this study, metabolites in different parts of P. lactiflora roots were imaged by air-assisted desorption electrospray ionization mass spectrometry imaging (AFADESI-MSI) to acquire full-scan MS1 data. They were classified by a mass defect filtering (MDF) model into two precursor ion lists (PILs), which guided metabolite identification using ultrahigh-performance liquid chromatography-quadrupole time-of-flight tandem mass spectrometry (UHPLC-Q-TOF-MS/MS). Ultimately, 92 metabolites were identified, and distributions of monoterpenoids and tannins were revealed. From the root-tip segment (S) to the rhizome-proximal segment (L), metabolites exhibited a spatial transition from diffuse to annular distribution, with enhanced tissue specificity. Furthermore, 19 differential metabolites were screened and characterized. This study facilitates sustainable utilization of P. lactiflora resources and offers insights for plant metabolomics.