We performed mass spectrometric imaging (MSI) to localize ginsenosides (Rb(1), Rb(2) or Rc, and Rf) in cross-sections of the Panax ginseng root at a resolution of 100 microm using matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS). Tandem mass spectrometry (MS/MS) of alkali metal-adducted ginsenoside ions revealed structural information of the corresponding saccharides and aglycone. MALDI-MSI confirmed that ginsenosides were located more in the cortex and the periderm than that in the medulla of a lateral root. In addition, it revealed that localization of ginsenosides in a root tip (diameter, 2.7 mm) is higher than that in the center of the root (diameter, 7.3 mm). A quantitative difference was detected between localizations of protopanaxadiol-type ginsenoside (Rb(1), Rb(2), or Rc) and protopanaxatriol-type ginsenoside (Rf) in the root. This imaging approach is a promising technique for rapid evaluation and identification of medicinal saponins in plant tissues.

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