title: The antioxidants of legume nodule mitochondria.
abstract: The mitochondria of legume root nodules are critical to sustain the energy-intensive process of nitrogen fixation. They also generate reactive oxygen species at high rates and thus require the protection of antioxidant enzymes and metabolites. We show here that highly purified mitochondria from bean nodules (Phaseolus vulgaris L. cv. Contender x Rhizobium leguminosarum bv. phaseoli strain 3622) contain ascorbate peroxidase primarily in the inner membrane (with lesser amounts detected occasionally in the matrix), guaiacol peroxidases in the outer membrane and matrix, and manganese superoxide dismutase (MnSOD) and an ascorbate-regenerating system in the matrix. This regenerating system relies on homoglutathione (instead of glutathione) and pyridine nucleotides as electron donors and involves the enzymes monodehydroascorbate reductase, dehydroascorbate reductase, and homoglutathione reductase. Homoglutathione is synthesized in the cytosol and taken up by the mitochondria and bacteroids. Although bacteroids synthesize glutathione, it is not exported to the plant in significant amounts. We propose a model for the detoxification of peroxides in nodule mitochondria in which membrane-bound ascorbate peroxidase scavenges the peroxide formed by the electron transport chain using ascorbate provided by L-galactono-1,4-lactone dehydrogenase in the inner membrane. The resulting monodehydroascorbate and dehydroascorbate can be recycled in the matrix or cytosol. In the matrix, the peroxides formed by oxidative reactions and by MnSOD may be scavenged by specific isozymes of guaiacol peroxidase, ascorbate peroxidase, and catalase.
authors.affiliation: Departamento de Nutrición Vegetal, Estación Experimental de Aula Dei, CSIC, Zaragoza, Spain.
authors.forename: I
authors.initials: I
authors.lastname: Iturbe-Ormaetxe
authors.forename: M A
authors.initials: MA
authors.lastname: Matamoros
authors.forename: M C
authors.initials: MC
authors.lastname: Rubio
authors.forename: D A
authors.initials: DA
authors.lastname: Dalton
authors.forename: M
authors.initials: M
authors.lastname: Becana
mesh_terms: D000975:Antioxidants / Q000378:metabolism*; D060387:Ascorbate Peroxidases; D002374:Catalase / Q000378:metabolism; D003600:Cytosol / Q000201:enzymology; D003576:Electron Transport Complex IV / Q000378:metabolism; D007887:Fabaceae / Q000201:enzymology / Q000378:metabolism*; D005978:Glutathione / Q000031:analogs & derivatives* / Q000096:biosynthesis; D007527:Isoenzymes / Q000378:metabolism; D008291:Malate Dehydrogenase / Q000378:metabolism; D008565:Membrane Proteins / Q000378:metabolism; D008928:Mitochondria / Q000378:metabolism*; D009245:NADH Dehydrogenase / Q000378:metabolism; D009247:NADH, NADPH Oxidoreductases / Q000378:metabolism; D009586:Nitrogen Fixation / Q000502:physiology; D010088:Oxidoreductases / Q000378:metabolism; D010453:Peptide Synthases / Q000378:metabolism; D009195:Peroxidase / Q000378:metabolism; D010544:Peroxidases / Q000378:metabolism; D018517:Plant Roots / Q000201:enzymology / Q000378:metabolism* / Q000382:microbiology; D017382:Reactive Oxygen Species / Q000378:metabolism; D013482:Superoxide Dismutase / Q000378:metabolism; D013559:Symbiosis
chemical_list: D000975:Antioxidants; D007527:Isoenzymes; D008565:Membrane Proteins; D017382:Reactive Oxygen Species; C402172:homoglutathione; D010088:Oxidoreductases; D008291:Malate Dehydrogenase; D010544:Peroxidases; C121048:guaiacol peroxidase; D060387:Ascorbate Peroxidases; D002374:Catalase; D009195:Peroxidase; D013482:Superoxide Dismutase; D009247:NADH, NADPH Oxidoreductases; C023927:monodehydroascorbate reductase (NADH); D009245:NADH Dehydrogenase; C020666:glutathione dehydrogenase (ascorbate); D003576:Electron Transport Complex IV; D010453:Peptide Synthases; C402171:homoglutathione synthase; D005978:Glutathione