Plant Physiology Preview
Published on January 23, 2003; 10.1104/pp.010538
Received June 26, 2002
Returned for revision September 9, 2002
Accepted November 21, 2002
In Plants, 3-O-Methylglucose Is Phosphorylated by Hexokinase But Not Perceived as a Sugar
Sandra Cortès , Marina Gromova , Adeline Evrard , Claude Roby *, Alain Heyraud , Dominique B. Rolin , Philippe Raymond , and Renaud M. Brouquisse
Commissariat à l'Energie Atomique, Centre National de la Recherche Scientifique, and Université Joseph Fourier, Unité Mixte de Recherche 5019 Physiologie Cellulaire Végétale, 17 rue des Martyrs, 38054 Grenoble cedex 9, France (S.C., M.G., A.E., C.R.); Centre National de la Recherche Scientifique, Unité Propre de Recherche 5301 Centre de Recherches sur les Macromolécules Végétales, Boîte Postale 53, 38041 Grenoble cedex 9, France (A.H.); and Institut National de la Recherche Agronomique and Université Victor Segalen Bordeaux 2, Unité Mixte de Recherche 619 Biotechnologie et Physiologie Végétales, Boîte Postale 81, 33883 Villenave d'Ornon cedex, France (D.B.R., P.R., R.M.B.)
* Corresponding author; email: croby{at}cea.fr.
In plants, sugars are the main respiratory substrates and important signaling molecules in the regulation of carbon metabolism. Sugar signaling studies suggested that sugar sensing involves several key components, among them hexokinase (HXK). Although the sensing mechanism of HXK is unknown, several experiments support the hypothesis that hexose phosphorylation is a determining factor. Glucose (Glc) analogs transported into cells but not phosphorylated are frequently used to test this hypothesis, among them 3-O-methyl-Glc (3-OMG). The aim of the present work was to investigate the effects and fate of 3-OMG in heterotrophic plant cells. Measurements of respiration rates, protein and metabolite contents, and protease activities and amounts showed that 3-OMG is not a respiratory substrate and does not contribute to biosynthesis. Proteolysis and lipolysis are induced in 3-OMG-fed maize (Zea mays L. cv DEA) roots in the same way as in sugar-starved organs. However, contrary to the generally accepted idea, phosphorous and carbon nuclear magnetic resonance experiments and enzymatic assays prove that 3-OMG is phosphorylated to 3-OMG-6-phosphate, which accumulates in the cells. Insofar as plant HXK is involved in sugar sensing, these findings are discussed on the basis of the kinetic properties because the catalytic efficiency of HXK isolated from maize root tips is five orders of magnitude lower for 3-OMG than for Glc and Man.
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