Development and Application of a High-Resolution Imaging Mass Spectrometer for the Study of Plant Tissues

Abstract

Matrix-assisted laser desorption/ionization (MALDI) mass spectrometry imaging (MSI) or imaging mass spectrometry (imaging MS) has been a powerful tool to map the spatial distribution of molecules on the surface of biological materials. This technique has frequently been applied to animal tissue slices for the purpose of mapping proteins, peptides, lipids, sugars or small metabolites to find disease-specific biomarkers or to study drug metabolism. Recently, it has also been applied to intact plant tissues or thin slices thereof using commercial mass spectrometers. The present work is concerned with the refinement of MALDI/laser desorption/ionization (LDI)-Fourier transform ion cyclotron resonance (FTICR)-MS incorporating certain specific features namely, ultra-high mass resolution (>100,000), ultra-high molecular mass accuracy (<1 p.p.m.) and high spatial resolution (<10 µm) for imaging MS of plant tissues. Employing an in-house built mass spectrometer, the imaging MS analysis of intact Arabidopsis thaliana tissues, namely etiolated seedlings and roots of seedlings, glued to a small transparent ITO (indium tin oxide)-coated conductive glass was performed. A matrix substance was applied to the vacuum-dried intact tissues by sublimation prior to the imaging MS analysis. The images of various small metabolites representing their two-dimensional distribution on the dried intact tissues were obtained with or without different matrix substances. The effects of MALDI matrices on the ionization of small metabolites during imaging MS acquisition are discussed.

Cell-specific localization of alkaloids in Catharanthus roseus stem tissue measured with Imaging MS and Single-cell MS

“…The space resolution of Imaging MS was 20 μm. MS images were reconstituted using an in-house software called LabMSI (22). Target mass peaks were detected in a bin size = 0.02.…”

“…Recent imaging MS revealed localization of many secondary metabolites in the rhizome of Glycyrrhiza glabra, with high resolution of about 20 μm (21). We have also reported the localization of metabolites at the cellular level of Arabidopsis tissues (22).…”

The complexity of intercellular localisation of alkaloids revealed by single‐cell metabolomics

“…In the present study, we have applied state-of-the-art methods of Imaging MS and single-cell MS for detecting metabolites in situ at the cellular level in leaf tissue of C. roseus as well as the stem tissue (Mizuno et al, 2008;Fujii et al, 2015;Takahashi et al, 2015;Yamamoto et al, 2016). By improving methods of laser irradiation for Imaging MS and of micro-capillary and video-assisted system for single-cell MS, we successfully elucidated single-cell-specific TIA localisation in the leaf tissue of C. roseus.…”

High-resolution MALDI mass spectrometry imaging of gallotannins and monoterpene glucosides in the root of Paeonia lactiflora

“…For plant tissues with numerous well-defined compartments, improvement in spatial resolution down to the cellular level provides access to a much greater chemical detail and therefore holds great potential to reveal the functions of tissue/cell-specific metabolites. For instance, asymmetric metabolic features in the cross section of maize leaf were mapped at 5 μm spatial resolution with an oversampling method18; C 29 alkane distribution on surface of single pollen grains of Arabidopsis was resolved at ~12 μm spatial resolution19; as well as various metabolite distributions on intact seedling of A. thaliana were visualized below 10 μm spatial resolution20. Likewise, tissue-specific localization of free flavonoids in rhizome of liquorice was visualized in the cork layer with 10 μm laser pixel resolution6 and at 5 μm pixel resolution metabolites in wheat seed were visualized21.…”