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BIOCHEMICAL PROCESSES AND MACROMOLECULAR STRUCTURES

Alterations in Cytosolic Glucose-Phosphate Metabolism Affect Structural Features and Biochemical Properties of Starch-Related Heteroglycans^1,[W]

Max-Planck Institute of Molecular Plant Physiology (A.N.-N., A.R.F.) and Department of Plant Physiology (J.F., J.A., M.S., M.S.), University of Potsdam, 14476 Potsdam-Golm, Germany

The cytosolic pools of glucose-1-phosphate (Glc-1-P) and glucose-6-phosphate are essential intermediates in several biosynthetic paths, including the formation of sucrose and cell wall constituents, and they are also linked to the cytosolic starch-related heteroglycans. In this work, structural features and biochemical properties of starch-related heteroglycans were analyzed as affected by the cytosolic glucose monophosphate metabolism using both source and sink organs from wild-type and various transgenic potato (Solanum tuberosum) plants. In leaves, increased levels of the cytosolic phosphoglucomutase (cPGM) did affect the cytosolic heteroglycans, as both the glucosyl content and the size distribution were diminished. By contrast, underexpression of cPGM resulted in an unchanged size distribution and an unaltered or even increased glucosyl content of the heteroglycans. Heteroglycans prepared from potato tubers were found to be similar to those from leaves but were not significantly affected by the level of cPGM activity. However, external glucose or Glc-1-P exerted entirely different effects on the cytosolic heteroglycans when added to tuber discs. Glucose was directed mainly toward starch and cell wall material, but incorporation into the constituents of the cytosolic heteroglycans was very low and roughly reflected the relative monomeric abundance. By contrast, Glc-1-P was selectively taken up by the tuber discs and resulted in a fast increase in the glucosyl content of the heteroglycans that quantitatively reflected the level of the cytosolic phosphorylase activity. Based on ¹⁴C labeling experiments, we propose that in the cytosol, glucose and Glc-1-P are metabolized by largely separated paths.

² Present address: Department of Biochemistry, Faculty of Agriculture and Biology, Warsaw University of Life Sciences, 02–776 Warszawa, Poland.

The author responsible for distribution of materials integral to the findings presented in this article in accordance with the policy described in the Instructions for Authors (www.plantphysiol.org) is: Martin Steup (msteup{at}rz.uni-potsdam.de).

^[W] The online version of this article contains Web-only data.

www.plantphysiol.org/cgi/doi/10.1104/pp.108.127969

^* Corresponding author; e-mail msteup{at}rz.uni-potsdam.de.

Received August 11, 2008; accepted September 8, 2008; published September 19, 2008.

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