Antisense inhibition of enolase strongly limits the metabolism of aromatic amino acids, but has only minor effects on respiration in leaves of transgenic tobacco plants.
Enolase catalyses the reversible conversion of 2-phosphoglycerate and phosphoenolpyruvate in glycolysis. Phosphoenolpyruvate constitutes an important branch point in plant metabolism. It is converted to pyruvate by pyruvate kinase and organic acids by phosphoenolpyruvate carboxylase. Phosphoenolpyruvate also acts as a precursor for the synthesis of aromatic amino acids in plastids. Tobacco (Nicotiana tabacum) enolase antisense plants were analysed for changes in metabolite composition, respiration and photosynthetic parameters. Antisense repression resulted in up to a 95% reduction in total enolase activity. It also resulted in fundamental changes in foliar metabolism. Although 2-phosphoglycerate remained largely unaltered, there was a substantial decrease in phosphoenolpyruvate. The levels of aromatic amino acids and secondary phenylpropanoid metabolites that are derived from these compounds decreased strongly, as did branched chain amino acids. The level of pyruvate was unaltered, as was the rate of respiration. There were substantial increases in tricarboxylic acid cycle intermediates, including a 16-fold increase in isocitrate, an increase in the total free amino acid content, including a 14-fold increase in asparagine and glutamine, and a 50% decrease in free sugars. We conclude that a decrease in enolase activity affects secondary pathways, such as the shikimate branch of amino acid biosynthesis, but does not inhibit the rate of respiration.
Voll
Lars M
LM
Department of Biochemistry, Friedrich-Alexander-Universität Erlangen-Nürnberg, Staudtstr. 5, 91058 Erlangen, Germany.
Hajirezaei
Mohammad R
MR
Leibniz Institute of Plant Genetics and Crop Plant Research (IPK), 06466 Gatersleben, Germany.
Czogalla-Peter
Cäcilia
C
Leibniz Institute of Plant Genetics and Crop Plant Research (IPK), 06466 Gatersleben, Germany.
Lein
Wolfgang
W
Max-Planck Institute of Molecular Plant Physiology, Am Mühlenberg 1, 14476 Golm, Germany.
Stitt
Mark
M
Max-Planck Institute of Molecular Plant Physiology, Am Mühlenberg 1, 14476 Golm, Germany.
Sonnewald
Uwe
U
Department of Biochemistry, Friedrich-Alexander-Universität Erlangen-Nürnberg, Staudtstr. 5, 91058 Erlangen, Germany.
Börnke
Frederik
F
Department of Biochemistry, Friedrich-Alexander-Universität Erlangen-Nürnberg, Staudtstr. 5, 91058 Erlangen, Germany.
D024322:Amino Acids, Aromatic / Q000378:metabolism*; D001483:Base Sequence; D050260:Carbohydrate Metabolism; D002245:Carbon Dioxide / Q000378:metabolism; D002952:Citric Acid Cycle; D003600:Cytosol / Q000201:enzymology; D017931:DNA Primers / Q000235:genetics; D018744:DNA, Plant / Q000235:genetics; D017343:Genes, Plant; D020319:Oligodeoxyribonucleotides, Antisense / Q000235:genetics; D010641:Phenotype; D010728:Phosphoenolpyruvate / Q000378:metabolism; D010751:Phosphopyruvate Hydratase / Q000037:antagonists & inhibitors* / Q000235:genetics / Q000378:metabolism; D010788:Photosynthesis / Q000235:genetics; D018515:Plant Leaves / Q000378:metabolism; D030821:Plants, Genetically Modified; D012765:Shikimic Acid / Q000378:metabolism; D014026:Nicotiana / Q000235:genetics* / Q000378:metabolism*
D024322:Amino Acids, Aromatic; D017931:DNA Primers; D018744:DNA, Plant; D020319:Oligodeoxyribonucleotides, Antisense; D002245:Carbon Dioxide; D012765:Shikimic Acid; D010728:Phosphoenolpyruvate; D010751:Phosphopyruvate Hydratase
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