SUMMARYThe present paper describes matrix-free laser desorption/ionisation mass spectrometric imaging (LDI-MSI) of highly localized UV-absorbing secondary metabolites in plant tissues at single-cell resolution. The scope and limitations of the method are discussed with regard to plants of the genus Hypericum. Naphthodianthrones such as hypericin and pseudohypericin are traceable in dark glands on Hypericum leaves, placenta, stamens and styli; biflavonoids are also traceable in the pollen of this important phytomedical plant. The highest spatial resolution achieved, 10 lm, was much higher than that achieved by commonly used matrix-assisted laser desorption/ionization (MALDI) imaging protocols. The data from imaging experiments were supported by independent LDI-TOF/MS analysis of cryo-sectioned, laser-microdissected and freshly cut plant material. The results confirmed the suitability of combining laser microdissection (LMD) and LDI-TOF/MS or LDI-MSI to analyse localized plant secondary metabolites. Furthermore, Arabidopsis thaliana was analysed to demonstrate the feasibility of LDI-MSI for other commonly occurring compounds such as flavonoids. The organspecific distribution of kaempferol, quercetin and isorhamnetin, and their glycosides, was imaged at the cellular level.

We have developed a method to visualize matrix-assisted laser desorption ionization imaging mass spectrometry (MALDI IMS) data aligned with optically determinable tissue structures in three dimensions. Details of the methodology are exemplified using the 3-D reconstruction of myelin basic protein (MBP) in the corpus callosum of a mouse brain. In this procedure, optical images obtained from serial coronal sections are first aligned to each other to reconstruct a surface of the corpus callosum from segmented contours of the aligned images. The MALDI IMS data are then coregistered to the optical images and superimposed into the surface to create the final 3-D visualization. Correlating proteomic data with anatomical structures provides a more comprehensive understanding of healthy and pathological brain functions, and holds promise to be utilized in more complex anatomical arrangements. (J Am Soc Mass Spectrom 2005, 16, 1093-1099

The global yield of bananas-one of the most important food crops-is severely hampered by parasites, such as nematodes, which cause yield losses up to 75%. Plant-nematode interactions of two banana cultivars differing in susceptibility to Radopholus similis were investigated by combining the conventional and spatially resolved analytical techniques 1 H NMR spectroscopy, matrixfree UV-laser desorption/ionization mass spectrometric imaging, and Raman microspectroscopy. This innovative combination of analytical techniques was applied to isolate, identify, and locate the bananaspecific type of phytoalexins, phenylphenalenones, in the R. similiscaused lesions of the plants. The striking antinematode activity of the phenylphenalenone anigorufone, its ingestion by the nematode, and its subsequent localization in lipid droplets within the nematode is reported. The importance of varying local concentrations of these specialized metabolites in infected plant tissues, their involvement in the plant's defense system, and derived strategies for improving banana resistance are highlighted.plant protection | induced plant defense | matrix-free LDI-MSI

Polar headgroups of free glycosyl-phosphatidylinositol (GPI) lipids or protein-bound GPI membrane anchors have been shown to exhibit insulin-mimetic activity in different cell types. However, elucidation of the molecular mode of action of these phospho-inositolglycan (PIG) molecules has been hampered by 1) lack of knowledge of their exact structure; 2) variable action profiles; and 3) rather modest effects. In the present study, these problems were circumvented by preparation of PIG-peptides (PIG-P) in sufficient quantity by sequential proteolytic (V8 protease) and lipolytic (phosphatidylinositol-specific phospholipase C) cleavage of the GPI-anchored plasma membrane protein, Gce1p, from the yeast Saccharomyces cerevisiae. The structure of the resulting PIG-P, NH2-Tyr-Cys-Asn-ethanolamine-PO4-6(Man1-2)Man1-2Man1-+ ++6Man1-4GlcNH(2)1-6myo-inositol-1,2-cyclicPO4, was revealed by amino acid analysis and Dionex exchange chromatography of fragments generated enzymatically or chemically from the neutral glycan core and is in accordance with the known consensus structures of yeast GPI anchors. PIG-P stimulated glucose transport and lipogenesis in normal, desensitized and receptor-depleted isolated rat adipocytes, increased glycerol-3-phosphate acyltransferase activity and translocation of the glucose transporter isoform 4, and inhibited isoproterenol-induced lipolysis and protein kinase A activation in adipocytes. Furthermore, PIG-P was found to stimulate glucose transport in isolated rat cardiomyocytes and glycogenesis and glycogen synthase in isolated rat diaphragms. The concentration-dependent effects of the PIG-P reached 70-90% of the maximal insulin activity with EC50-values of 0.5-5 microM. Chemical or enzymic cleavages within the glycan or peptide portion of the PIG-P led to decrease or loss of activity. The data demonstrate that PIG-P exhibits a potent insulin-mimetic activity which covers a broad spectrum of metabolic insulin actions on glucose transport and metabolism.

The detailed characterization of macromolecules plays an important role for synthetic chemists to define and specify the structure and properties of the successfully synthesized polymers. The search for new characterization techniques for polymers is essential for the continuation of the development of improved synthesis methods. The application of tandem mass spectrometry for the detailed characterization of synthetic polymers using the soft ionization techniques matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS) and electrospray ionization mass spectrometry (ESI-MS), which became the basic tools in proteomics, has greatly been increased in recent years and is summarized in this perspective. Examples of a variety of homopolymers, such as poly(methyl methacrylate), poly(ethylene glycol), as well as copolymers, e.g. copolyesters, are given. The advanced mass spectrometric techniques described in this review will presumably become one of the basic tools in polymer chemistry in the near future.

In order to achieve a comprehensive description of biological tissue, spectral information about proteins, lipids, nucleic acids, and other biochemical components need to be obtained concurrently. Different analytical techniques may be combined to record complementary information of the same sample. Established techniques, which can be utilized to elucidate the biochemistry of tissue samples are, for instance, MALDI-TOF-MS and Raman microscopic imaging. With this contribution, we combine these two techniques for the first time. The combination of both techniques allows the utilization and interpretation of complementary information (i.e., the information about the protein composition derived from the Raman spectra with data of the lipids analyzed by the MALDI-TOF measurements). Furthermore, we demonstrate how spectral information from MALDI-TOF experiments can be utilized to interpret Raman spectra.

The number of proteomics studies concerning human brain samples has been increasing in recent years, in particular in the discovery of biomarkers for neurological diseases. The human brain samples are obtained from brain banks, which are interested in providing high quality human nervous tissue. In order to provide brain banks as well as scientists working in the proteomics field with measures for tissue quality, the critical factors after death, the effect of post-mortem interval (PMI) and storage temperature on the human brain proteome were investigated. This study was focused on the gray matter of the frontal cortex. The PMI was artificially prolonged from the time of autopsy (2 h after death) by storing samples at 4 degrees C or room temperature over 18, 24, and 48 h. The samples were analyzed by 2-D DIGE using a pH 4-7 gradient, revealing a time course of quantitative protein changes. The degradation of three proteins, peroxiredoxin-1, stathmin, and glial fibrillary acidic protein were further confirmed by Western-blot analysis. Proteins vulnerable to PMI were analyzed by the 2-D DIGE analysis of cortex samples from three donors, and were derived from a variety of functional groups, including metabolic, structural, stress response, antioxidants, synaptosomal, and neuronal proteins.

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