Professor of Chemistry, Professor of Biochemistry & Molecular Biology
Founder and Co-director
W.M. Keck Institute for Proteomics Technology and Applications
George Washington University

Date: Tuesday, September 18, 2007
Time: 10AM-11AM
Location: Molecular Science and Engineering ("M Building"), Room 3201A

"In Vivo Imaging of Plant Metabolism with Mass Spectrometry"

Abstract: To better understand plant metabolism changes due to genetic modifications, environmental stress such as starvation or drought conditions, or ecological challenges (plant-herbivore and plant-insect interactions), tools are required that can map the spatial and temporal distribution of diverse chemical species in a living organism. Mass spectrometry offers unique capabilities in terms of simultaneous detection of numerous biochemical components, the potential for their structural identification, high sensitivity and broad dynamic range. To utilize mass spectrometry for in vivo analysis of metabolites, atmospheric pressure ion sources are being developed. In this presentation two new ion sources, atmospheric pressure infrared matrix-assisted laser desorption ionization (AP IR-MALDI) and laser ablation electrospray ionization (LAESI), are described for the rapid identification of a wide array of metabolites, including simple carbohydrates, oligosaccharides, amino acids, organic acids, lipids, flavonoids and a variety of other compounds, in plants. With AP IR-MALDI we showed examples of detecting intermediates in cellular respiration (e.g., the citric acid cycle with 70% coverage) and in a variety of other metabolic pathways. We also demonstrated the ability of these methods to follow plant transpiration and to image molecular distributions in plant tissue. In biological fluids, LAESI showed detection capabilities for a variety of molecular classes and size ranges (up to 66 kDa) with low femtomole detection limits and quantitation capabilities with a four-decade dynamic range. With LAESI we also performed in vivo spatial profiling (on leaf, stem and root) of metabolites in a French marigold (Tagetes patula) seedling. Both methods are readily applicable to diverse biological tissues. Future studies include metabolism of genetically modified organisms, ecological interactions, physiological investigations, clinical applications, pharmacokinetics studies, subcellular detection and combination of these techniques with laser surgery.
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