Visualizing the spatial distribution of metabolites in Clausena lansium (Lour.) skeels using matrix-assisted laser desorption/ionization mass spectrometry imaging.

Clausena lansium (Lour.) Skeels (Rutaceae) is a natural bioactive plant. Its roots, stems, leaves, and seeds are widely used in Chinese traditional and folk medicine. Although the characterization and functional analysis of bioactive components in Clausena lansium (Lour.) Skeels has been widely reported, the spatial distribution of these compounds within the main plant tissues remains undefined. Here, we adopted matrix-assisted laser desorption/ionization-mass spectrometry imaging (MALDI-MSI) to reveal the spatial distribution of active alkaloids, coumarins, sugars and organic acids in C. lansium. Using a combined wet and dry matrix covering method to enhance sensitivity, we detected alkaloids throughout the fruit including 3-methylcarbazole and murrastinine which were especially rich in the kernel tissues but were restricted to the stem xylem and medulla and in the leaf epidermal region. Interestingly, murrayanine and heptaphylline were mainly found in pulp tissues with very low content in the stems and leaves while girinimbine was only distributed within the outer kernel skin. Coumarins were mainly distributed in the fruit pericarp and leaf vein tissues but with no clear spatial specificity in stems. Lastly, hexoses were mainly evident in the fruit pulp, although sucrose was also found in the pericarp, pulp, and pulp fibers with citric acid being distributed throughout the fruit. The accurate spatial and chemical information obtained provides new insights into the specific accumulation of metabolites in individual tissues.