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The complexity of intercellular localization of alkaloids revealed by single cell metabolomics.

Catharanthus roseus is a medicinal plant well known for producing bioactive compounds such as vinblastine and vincristine, which are classified as terpenoid indole alkaloids (TIAs). Although the leaves of this plant are the main source of these antitumor drugs, much remains unknown about how TIAs are biosynthesized from a central precursor, strictosidine, to various TIAs in planta. Here, we have succeeded in showing, for the first time in leaf tissue of C. roseus, cell-specific TIAs localization and accumulation with 10 μm spatial resolution Imaging mass spectrometry (Imaging MS) and live single cell mass spectrometry (Single-cell MS). These metabolomic studies revealed that most TIA precursors (iridoids) are localized in the epidermal cells, but major TIAs including serpentine and vindoline are localized instead in idioblast cells. Interestingly, the central TIA intermediate strictosidine also accumulates in both epidermal and idioblast cells of C. roseus. Moreover, we also found that vindoline accumulation increases in laticifer cells as the leaf expands. These discoveries highlight the complexity of intercellular localization in plant specialized metabolism. This article is protected by copyright. All rights reserved.