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Published on September 19, 2008; 10.1104/pp.108.127969

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Received August 11, 2008
Accepted September 8, 2008

Alterations in cytosolic glucose phosphate metabolism affect structural features and biochemical properties of starch-related heteroglycans

Joerg Fettke , Adriano Nunes-Nesi , Jessica Alpers , Michal Szkop , Alisdair R. Fernie , and Martin Steup *

Max-Planck Institute of Molecular Plant Physiology and Department of Plant Physiology, University of Potsdam, 14476 Potsdam-Golm, Germany

* Corresponding author; email: msteup{at}rz.uni-potsdam.de.

The cytosolic pools of glucose 1-phosphate and glucose 6-phosphate are essential intermediates in several biosynthetic paths, including formation of sucrose and cell wall constitutents, and they are also linked to the cytosolic starch-related heteroglycans. In this communication 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 from various transgenic potato (Solanum tuberosum L.) 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 the cPGM activity. However, external glucose or glucose 1-phosphate exerted entirely different effects on the cytosolic heteroglycans when added to tuber discs. Glucose was directed mainly towards 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, glucose 1-phosphate 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 phosphosphorylase activity. Based on 14C-labeling experiments we propose that in the cytosol glucose and glucose 1-phosphate are metabolized by largely separated paths.




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J. Fettke, M. Hejazi, J. Smirnova, E. Hochel, M. Stage, and M. Steup
Eukaryotic starch degradation: integration of plastidial and cytosolic pathways
J. Exp. Bot., July 1, 2009; 60(10): 2907 - 2922.
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