Quantitative Single-Cell\nMass Spectrometry Provides\na Highly Resolved Analysis of Natural Product Biosynthesis Partitioning\nin Plants

Plants produce an extraordinary array of natural products\n(specialized\nmetabolites). Notably, these structurally complex molecules are not\nevenly distributed throughout plant tissues but are instead synthesized\nand stored in specific cell types. Elucidating both the biosynthesis\nand function of natural products would be greatly facilitated by tracking\nthe location of these metabolites at the cell-level resolution. However,\ndetection, identification, and quantification of metabolites in single\ncells, particularly from plants, have remained challenging. Here,\nwe show that we can definitively identify and quantify the concentrations\nof 16 molecules from four classes of natural products in individual\ncells of leaf, root, and petal of the medicinal plant Catharanthus roseus using a plate-based single-cell\nmass spectrometry method. We show that identical natural products\nshow substantially different patterns of cell-type localization in\ndifferent tissues. Moreover, we show that natural products are often\nfound in a wide range of concentrations across a population of cells,\nwith some natural products at concentrations of over 100 mM per cell.\nThis single-cell mass spectrometry method provides a highly resolved\npicture of plant natural product biosynthesis partitioning at a cell-specific\nresolution.