Imaging Mass Spectrometry Reveals In Situ Conversion of Glucosinolates to Bioactive Isothiocyanates in Cabbage

Cabbage (Brassica oleracea var. capitata) contains glucosinolates (GSLs) such as glucoraphanin and sinigrin, which serve as precursors to bioactive isothiocyanates (ITCs), including sulforaphane (SFN) and allyl isothiocyanate (AITC). Upon cellular rupture, GSLs come into contact with myrosinase, resulting in ITC formation as part of the plant defense response. While this process has been studied biochemically, its spatial manifestation within plant tissues has not been directly visualized. In this study, GSL levels in intact and ruptured cabbage samples were quantified by LC-MS, and imaging mass spectrometry (IMS) was used to map the GSLs and ITCs in tissue sections. GSLs were localized mainly in intact regions, whereas ITCs were detected predominantly in ruptured areas, showing reciprocal spatial distributions. These results provide the first direct visualization of GSL-to-ITC conversion in plant tissues and demonstrate the utility of IMS for studying enzymatic biochemical transformations relevant to plant defense and food functionality.