Journal Article

Analysis of Cytosolic Heteroglycans from Leaves of Transgenic Potato (<i>Solanum tuberosum</i> L.) Plants that Under- or Overexpress the Pho 2 Phosphorylase Isozyme

Joerg Fettke, Simon Poeste, Nora Eckermann, Axel Tiessen, Markus Pauly, Peter Geigenberger and Martin Steup

in Plant and Cell Physiology

Published on behalf of Japanese Society of Plant Physiologists

Volume 46, issue 12, pages 1987-2004
Published in print December 2005 | ISSN: 0032-0781
Published online December 2005 | e-ISSN: 1471-9053 | DOI: http://dx.doi.org/10.1093/pcp/pci214
Analysis of Cytosolic Heteroglycans from Leaves of Transgenic Potato (Solanum tuberosum L.) Plants that Under- or Overexpress the Pho 2 Phosphorylase Isozyme

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During starch degradation, chloroplasts export neutral sugars into the cytosol where they appear to enter a complex glycan metabolism. Interactions between glycans and glucosyl transferases residing in the cytosol were studied by analyzing transgenic potato (Solanum tuberosum L.) plants that possess either decreased or elevated levels of the cytosolic (Pho 2) phosphorylase isoform. Water-soluble heteroglycans (SHGs) were isolated from these plants and were characterized. SHG contains, as major constituents, arabinose, rhamnose, galactose and glucose. Non-aqueous fractionation combined with other separation techniques revealed a distinct pool of the SHG that is located in the cytosol. Under in vitro conditions, the cytosolic heteroglycans act as glucosyl acceptor selectively for Pho 2. Acceptor sites were characterized by a specific hydrolytic degradation following the Pho 2-catalyzed glucosyl transfer. The size distribution of the cytosolic SHG increased during the dark period, indicating a distinct metabolic activity related to net starch degradation. Antisense inhibition of Pho 2 resulted in increased glucosyl and rhamnosyl contents of the glycans. Overexpression of Pho 2 decreased the content of both residues. Compared with the wild type, in both types of transgenic plants the size of the cytosolic glycans was increased.

Keywords: Carbohydrate metabolism; Cytosolic heteroglycans; Overexpression; Phosphorylase isozymes; Solanum tuberosum L.; Starch metabolism; DPE2, amylomaltase, glucanotransferase or transglucosidase (EC 2.4.1.25); FFF, field flow fractionation; FITC, fluorescein isothiocyanate; HPAEC-PAD, high-performance anion-exchange chromatography with pulsed amperometric detection; MALLS, multiangle laser light scattering; SHG, water-soluble heteroglycans; SHG0, water-soluble heteroglycans (including monosaccharides and disaccharides); SHGL, water-soluble heteroglycans (large size fraction); SHGS water-soluble heteroglycans (small size fraction); SHGT water-soluble heteroglycans (total fraction)

Journal Article.  13480 words.  Illustrated.

Subjects: Biochemistry ; Molecular and Cell Biology ; Plant Sciences and Forestry

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