title: Analysis of cytosolic heteroglycans from leaves of transgenic potato (Solanum tuberosum L.) plants that under- or overexpress the Pho 2 phosphorylase isozyme.
abstract: 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.
authors.affiliation: Department of Plant Physiology, Institute of Biochemistry and Biology, University of Potsdam, Karl-Liebknecht-Str. 24-25, Building 20, D-14476 Potsdam-Golm, Germany.
authors.forename: Joerg
authors.initials: J
authors.lastname: Fettke
authors.forename: Simon
authors.initials: S
authors.lastname: Poeste
authors.forename: Nora
authors.initials: N
authors.lastname: Eckermann
authors.forename: Axel
authors.initials: A
authors.lastname: Tiessen
authors.forename: Markus
authors.initials: M
authors.lastname: Pauly
authors.forename: Peter
authors.initials: P
authors.lastname: Geigenberger
authors.forename: Martin
authors.initials: M
authors.lastname: Steup
mesh_terms: D000222:Adaptation, Physiological / Q000502:physiology; D001089:Arabinose / Q000378:metabolism; D015152:Blotting, Northern; D002236:Carbohydrate Conformation; D003600:Cytosol / Q000737:chemistry* / Q000378:metabolism; D004591:Electrophoresis, Polyacrylamide Gel; D005690:Galactose / Q000378:metabolism; D018506:Gene Expression Regulation, Plant; D005947:Glucose / Q000378:metabolism; D006026:Glycoside Hydrolases / Q000494:pharmacology; D007150:Immunohistochemistry; D007527:Isoenzymes / Q000235:genetics / Q000378:metabolism; D006005:Phosphorylases / Q000235:genetics* / Q000378:metabolism; D018515:Plant Leaves / Q000737:chemistry* / Q000166:cytology / Q000378:metabolism; D030821:Plants, Genetically Modified; D011134:Polysaccharides / Q000032:analysis* / Q000378:metabolism; D012210:Rhamnose / Q000378:metabolism; D011198:Solanum tuberosum / Q000201:enzymology / Q000235:genetics* / Q000378:metabolism*; D013379:Substrate Specificity
chemical_list: D007527:Isoenzymes; D011134:Polysaccharides; D001089:Arabinose; D006005:Phosphorylases; D006026:Glycoside Hydrolases; C100181:pullulanase; C019713:alpha-N-arabinofuranosidase; D005947:Glucose; D012210:Rhamnose; D005690:Galactose