Unraveling spatial distribution of metabolites of Taraxacum mongolicum Hand.-Mazz by matrix-assisted laser desorption/ionization mass spectrometry imaging.

Taraxacum mongolicum Hand.-Mazz (T. mongolicum), as a medical herb and edible vegetable for centuries, has a wide variety of bioactive compounds. Visualization of the spatial dynamics of metabolites can promote our understanding of the compartmentalization of metabolic networks in plant tissue. Meanwhile, it will provide a highly informative approach to discovering the metabolic heterogeneity during the development of plants. This study aims to explore the spatial and temporal distribution patterns and spatiotemporal dynamics of metabolites in T. mongolicum roots and leaves. Matrix-assisted laser desorption/ionization mass spectrometry imaging (MALDI-MSI) was selected as an ideal tool for metabolite imaging. CHCA and DHAP were ultimately selected as the suitable mode matrices in positive and negative ion modes, respectively. A spatial resolution of 100 µm was used to image frozen sections of root tissue and leaf tissue imprints. A wide spectrum of metabolites, including organic acids, phenolic acids, flavonoids, amino acids, carbohydrates, and choline, were visualized for the first time. Meanwhile, the spatiotemporal dynamics of metabolites were characterized during the different developmental stages of the root. Furthermore, we established and applied a method for imaging leaf tissue, revealing three typical patterns of metabolite distribution in T. mongolicum leaves. These results not only reveal the heterogeneity of T. mongolicum tissues and their spatial metabolic networks, but also provide support for quality control, biosynthesis, and resource utilization.