title: Complex I-complex II ratio strongly differs in various organs of Arabidopsis thaliana.
abstract: In most studies, amounts of protein complexes of the oxidative phosphorylation (OXPHOS) system in different organs or tissues are quantified on the basis of isolated mitochondrial fractions. However, yield of mitochondrial isolations might differ with respect to tissue type due to varying efficiencies of cell disruption during organelle isolation procedures or due to tissue-specific properties of organelles. Here we report an immunological investigation on the ratio of the OXPHOS complexes in different tissues of Arabidopsis thaliana which is based on total protein fractions isolated from five Arabidopsis organs (leaves, stems, flowers, roots and seeds) and from callus. Antibodies were generated against one surface exposed subunit of each of the five OXPHOS complexes and used for systematic immunoblotting experiments. Amounts of all complexes are highest in flowers (likewise with respect to organ fresh weight or total protein content of the flower fraction). Relative amounts of protein complexes in all other fractions were determined with respect to their amounts in flowers. Our investigation reveals high relative amounts of complex I in green organs (leaves and stems) but much lower amounts in non-green organs (roots, callus tissue). In contrast, complex II only is represented by low relative amounts in green organs but by significantly higher amounts in non-green organs, especially in seeds. In fact, the complex I-complex II ratio differs by factor 37 between callus and leaf, indicating drastic differences in electron entry into the respiratory chain in these two fractions. Variation in amounts concerning complexes III, IV and V was less pronounced in different Arabidopsis tissues (quantification of complex V in leaves was not meaningful due to a cross-reaction of the antibody with the chloroplast form of this enzyme). Analyses were complemented by in gel activity measurements for the protein complexes of the OXPHOS system and comparative 2D blue native/SDS PAGE analyses using isolated mitochondria. We suggest that complex I has an especially important role in the context of photosynthesis which might be due to its indirect involvement in photorespiration and its numerous enzymatic side activities in plants.
authors.affiliation: Faculty of Natural Sciences, Institute of Plant Genetics, Leibniz Universität Hannover, 30419 Hannover, Germany.
authors.forename: Katrin
authors.initials: K
authors.lastname: Peters
authors.forename: Markus
authors.initials: M
authors.lastname: Niessen
authors.forename: Christoph
authors.initials: C
authors.lastname: Peterhänsel
authors.forename: Bettina
authors.initials: B
authors.lastname: Späth
authors.forename: Angela
authors.initials: A
authors.lastname: Hölzle
authors.forename: Stefan
authors.initials: S
authors.lastname: Binder
authors.forename: Anita
authors.initials: A
authors.lastname: Marchfelder
authors.forename: Hans-Peter
authors.initials: HP
authors.lastname: Braun
mesh_terms: D017360:Arabidopsis / Q000378:metabolism*; D029681:Arabidopsis Proteins / Q000378:metabolism*; D004579:Electron Transport; D042967:Electron Transport Complex I / Q000378:metabolism*; D015180:Electrophoresis, Gel, Two-Dimensional; D004591:Electrophoresis, Polyacrylamide Gel; D024101:Mitochondrial Proteins / Q000378:metabolism*; D010085:Oxidative Phosphorylation; D018515:Plant Leaves / Q000378:metabolism; D018517:Plant Roots / Q000378:metabolism; D018547:Plant Stems / Q000378:metabolism
chemical_list: D029681:Arabidopsis Proteins; D024101:Mitochondrial Proteins; D042967:Electron Transport Complex I