Abstract
Mass spectrometry (MS) imaging provides spatial and molecular information for a wide range of compounds. This tool can be used to investigate metabolic changes in plant physiology and environmental interactions. A major challenge in our study was to prepare tissue sections that were compatible with high spatial resolution analysis and therefore dedicated sample preparation protocols were established and optimized for the physicochemical properties of all major plant organs. We combined high spatial resolution (5 μm), in order to detect cellular features, and high mass accuracy (<2 ppm root mean square error), for molecular specificity. Mass spectrometry imaging experiments were performed in positive and negative ion mode. Changes in metabolite patterns during plant development were investigated for germination of oilseed rape. The detailed localization of more than 90 compounds allowed assignment to metabolic processes and indicated possible functions in plant tissues. The 'untargeted' nature of MS imaging allows the detection of marker compounds for the physiological status, as demonstrated for plant-pathogen interactions. Our images show excellent correlation with optical/histological examination. In contrast to previous MS imaging studies of plants, we present a complete workflow that covers multiple species, such as oilseed rape, wheat seed and rice. In addition, different major plant organs and a wide variety of compound classes were analyzed. Thus, our method could be used to develop a plant metabolite atlas as a reference to investigate systemic and local effects of pathogen infection or environmental stress.
Highlights
Plants are major suppliers of food and natural resources used in pharmaceuticals, cosmetics, and fine chemicals
The exact location of this pixel and the zoomed-in mass spectrum are provided in Electronic supplementary information (ESI), Fig. S1.† Additional single 10 μm spectra from cotyledon vasculature, nucellar tissue, seed coat, and emerging radicle are shown in the ESI, Fig. S2–S5.† Several compounds such as sinapine, methyl sinapate, cyclic spermidine conjugate, triacylglycerols and phosphatidylcholines were detected
We present an approach for Mass spectrometry (MS) imaging of plant metabolites that cover multiple mono- and dicot species, major plant organs and a wide variety of compound classes
Summary
Plants are major suppliers of food and natural resources used in pharmaceuticals, cosmetics, and fine chemicals. Wheat (Triticum aestivum) and oilseed rape (Brassica napus) to uncover biochemical mechanisms behind complex agronomical traits and phenotypes.[4] Important current issues in crop plant research are developmental plasticity,[5] and responses to abiotic[6] and biotic stress.[7] In contrast to genes, metabolites are the end products of cellular processes and can serve as direct signatures of biochemical activity.[8] Metabolomics studies are typically based on mass spectrometry (MS), hyphenated with techniques such as gas and liquid chromatography, covering an extensive variety of compound classes and concentration ranges In these studies, usually homogenized samples are used, resulting in a loss of spatial information. We discuss the idea of how our MS imaging approach could be used to build up an atlas of the plant metabolome as a reference to detect the systemic and local metabolic changes
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