Visualizing the Spatial Distribution of Metabolites in Angelica sinensis Roots by Matrix‐Assisted Laser Desorption/Ionization Mass Spectrometry Imaging

Angelica sinensis is one of the most popular traditional Chinese medicines (TCM) and has been extensively used to treat various diseases. Hundreds of endogenous ingredients have been isolated and identified from this herb, but their spatial distribution within the plant root is largely unknown. In this study, we tried to investigate and map within-tissue spatial distribution of metabolites in Angelica sinensis roots. After optimization of experiment conditions, the 1,5-diaminonaphthalene (1,5-DAN) was chosen as the matrix and was sprayed on the surface of root sections. Then matrix-assisted laser desorption/ionization mass spectrometry imaging (MALDI-MSI) was employed to perform in situ detection and obtain detail spatial distribution information of metabolites in Angelica sinensis roots. The spatial distributions of a wide range of metabolites including organic acids, amino acids, oligosaccharides, and phospholipids were characterized and visualized in Angelica sinensis roots. Majority of these metabolites were located in the phloem and xylem, while ferulic acid was mainly present in the cork layer. The results revealed a dramatic metabolic heterogeneity among different regions of the roots and distinct spatial distribution patterns of different metabolites. Additionally, the metabolic pathways involved in the biosynthesis of choline were also successfully localized and visualized. This study comprehensively characterized the spatial distribution of metabolites in Angelica sinensis roots, which would prompt the understanding of its chemical separation, biosynthesis, and pharmacological activities.