Plant and Cell Physiology Advance Access originally published online on October 17, 2005
Plant and Cell Physiology 2005 46(12):1987-2004; doi:10.1093/pcp/pci214
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Analysis of Cytosolic Heteroglycans from Leaves of Transgenic Potato (Solanum tuberosum L.) Plants that Under- or Overexpress the Pho 2 Phosphorylase Isozyme
1 Department of Plant Physiology, Institute of Biochemistry and Biology, University of Potsdam, Karl-Liebknecht-Str. 24-25, Building 20, D-14476 Potsdam-Golm, Germany
2 Max-Planck-Institute of Molecular Plant Physiology, Am Mühlenberg 1, D-14476 Potsdam-Golm, Germany
* Corresponding author: E-mail, msteup{at}rz.uni-potsdam.de; Fax, +49–331/977–2512
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.
3 These authors contributed equally to this work.
(Received August 26, 2005; Accepted October 6, 2005)
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