Mitochondrial Metabolism in Developing Embryos of Brassica napus

• Published in: The Journal of biological chemistry Vol. 281; no. 45; pp. 34040 - 34047
• Main Authors: Schwender, Jörg, Shachar-Hill, Yair, Ohlrogge, John B.
• Format: Journal Article
• Language: English
• Published: United States Elsevier Inc 10.11.2006; American Society for Biochemistry and Molecular Biology
• Subjects: Acetyl Coenzyme A - metabolism; Amino Acids - metabolism; Brassica napus - growth & development; Brassica napus - metabolism; Carbohydrate Metabolism; Carbon - metabolism; Carbon Isotopes - metabolism; Citric Acid Cycle; Culture Techniques; Cytosol - metabolism; Fatty Acids - metabolism; Gas Chromatography-Mass Spectrometry; Glucose - metabolism; Glycolysis; Isotope Labeling; Malates - metabolism; Mitochondria - metabolism; Models, Biological; Oxidative Phosphorylation; Protein-Serine-Threonine Kinases - metabolism; Pyruvic Acid - metabolism; Seeds - growth & development; Seeds - metabolism
• ISSN: 0021-9258; 1083-351X
• DOI: 10.1074/jbc.M606266200

The metabolism of developing plant seeds is directed toward transforming primary assimilatory products (sugars and amino acids) into seed storage compounds. To understand the role of mitochondria in this metabolism, metabolic fluxes were determined in developing embryos of Brassica napus. After labeling with [1,2-13C2]glucose + [U-13C6]glucose, [U-13C3]alanine, [U-13C5]glutamine, [15N]alanine, (amino)-[15N]glutamine, or (amide)-[15N]glutamine, the resulting labeling patterns in protein amino acids and in fatty acids were analyzed by gas chromatography-mass spectrometry. Fluxes through mitochondrial metabolism were quantified using a steady state flux model. Labeling information from experiments using different labeled substrates was essential for model validation and reliable flux estimation. The resulting flux map shows that mitochondrial metabolism in these developing seeds is very different from that in either heterotrophic or autotrophic plant tissues or in most other organisms: (i) flux around the tricarboxylic acid cycle is absent and the small fluxes through oxidative reactions in the mitochondrion can generate (via oxidative phosphorylation) at most 22% of the ATP needed for biosynthesis; (ii) isocitrate dehydrogenase is reversible in vivo; (iii) about 40% of mitochondrial pyruvate is produced by malic enzyme rather than being imported from the cytosol; (iv) mitochondrial flux is largely devoted to providing precursors for cytosolic fatty acid elongation; and (v) the uptake of amino acids rather than anaplerosis via PEP carboxylase determines carbon flow into storage proteins.