Intrastem Behavior of Monolignol Glucosides Visualized by Cryo-Secondary Ion Mass Spectrometry

Monolignol glucosides occur in plants as water-soluble, chemically stabilized forms of monolignols and have been discussed as storage and transport forms in lignification.However, these small molecules readily change their localization during common analytical pretreatments, and therefore, discussions based on cell-level intact distributions within stems have been limited.In this review, we summarize prior efforts to reveal intrastem behavior using cryo-secondary ion mass spectrometry which directly visualizes the instantaneous distribution in freeze-fixed samples, together with (i) tissue assignment by microscopic observations, (ii) selection of target m/z values based on the ionization behavior of authentic standards, and (iii) validation by chromatography measurements of serial tangential sections.In addition, cryo-secondary ion mass spectrometry equipped with gas cluster ion beam measurements provides high-resolution and threedimensional images.These approaches provide information on which tissues and cells contain what amounts of intrastem monolignol glucosides, and they contribute to re-examining and updating models for the transport, storage, and consumption of lignin precursors involved in lignin deposition.