Analysis of fructans from higher plants by matrix-assisted laser desorption/ionization mass spectrometry

In this communication both matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS) and high-performance anion-exchange chromatography (HPAEC) have been applied to analyze fructans from higher plants. Size distribution of a commercially available fructan preparation from Dahlia variabilis L. was determined by MALDI-MS. Molecular masses ranged from 2,000 up to 6,000 Da with a peak value of distribution at 2,635 Da. Essentially the same pattern was obtained using HPAEC. Low-molecular-weight fructans from onion bulbs (Allium cepa L.) were studied in more detail. Tissue extracts were analyzed by MALDI-MS without any analyte purification. Mass-spectra of both proteins and oligosaccharides were obtained. For identification, metastable ion scanning was performed. Neither deproteinization nor deionization of the samples affected the oligosaccharide pattern. Using HPAEC, a more complex oligosaccharide pattern was obtained because isomeric glycans were differentiated. However, the overall size distribution was similar to that obtained by MALDI-MS. In further experiments epidermal or parenchyma cell layers of the onion bulb were placed into matrix solution and were then subjected to MALDI-MS and metastable ion scanning as well. By taking this approach, analyte desorption was achieved immediately from plant tissue. Oligosaccharide mass spectra were essentially the same as those of the extracts. To our knowledge, this is the first time that MALDI-MS has been applied as a microprobe to plant tissue. Finally MALDI-MS analysis was performed using single-cell extracts from onion tissues without any purification of the analyte.