title: Multiple strategies to prevent oxidative stress in Arabidopsis plants lacking the malate valve enzyme NADP-malate dehydrogenase.
abstract: The nuclear-encoded chloroplast NADP-dependent malate dehydrogenase (NADP-MDH) is a key enzyme controlling the malate valve, to allow the indirect export of reducing equivalents. Arabidopsis thaliana (L.) Heynh. T-DNA insertion mutants of NADP-MDH were used to assess the role of the light-activated NADP-MDH in a typical C(3) plant. Surprisingly, even when exposed to high-light conditions in short days, nadp-mdh knockout mutants were phenotypically indistinguishable from the wild type. The photosynthetic performance and typical antioxidative systems, such as the Beck-Halliwell-Asada pathway, were barely affected in the mutants in response to high-light treatment. The reactive oxygen species levels remained low, indicating the apparent absence of oxidative stress, in the mutants. Further analysis revealed a novel combination of compensatory mechanisms in order to maintain redox homeostasis in the nadp-mdh plants under high-light conditions, particularly an increase in the NTRC/2-Cys peroxiredoxin (Prx) system in chloroplasts. There were indications of adjustments in extra-chloroplastic components of photorespiration and proline levels, which all could dissipate excess reducing equivalents, sustain photosynthesis, and prevent photoinhibition in nadp-mdh knockout plants. Such metabolic flexibility suggests that the malate valve acts in concert with other NADPH-consuming reactions to maintain a balanced redox state during photosynthesis under high-light stress in wild-type plants.
authors.affiliation: Department of Plant Physiology, FB5, University of Osnabrueck, D-49069 Osnabrueck, Germany.
authors.forename: Inga
authors.initials: I
authors.lastname: Hebbelmann
authors.forename: Jennifer
authors.initials: J
authors.lastname: Selinski
authors.forename: Corinna
authors.initials: C
authors.lastname: Wehmeyer
authors.forename: Tatjana
authors.initials: T
authors.lastname: Goss
authors.forename: Ingo
authors.initials: I
authors.lastname: Voss
authors.forename: Paula
authors.initials: P
authors.lastname: Mulo
authors.forename: Saijaliisa
authors.initials: S
authors.lastname: Kangasjärvi
authors.forename: Eva-Mari
authors.initials: EM
authors.lastname: Aro
authors.forename: Marie-Luise
authors.initials: ML
authors.lastname: Oelze
authors.forename: Karl-Josef
authors.initials: KJ
authors.lastname: Dietz
authors.forename: Adriano
authors.initials: A
authors.lastname: Nunes-Nesi
authors.forename: Phuc T
authors.initials: PT
authors.lastname: Do
authors.forename: Alisdair R
authors.initials: AR
authors.lastname: Fernie
authors.forename: Sai K
authors.initials: SK
authors.lastname: Talla
authors.forename: Agepati S
authors.initials: AS
authors.lastname: Raghavendra
authors.forename: Vera
authors.initials: V
authors.lastname: Linke
authors.forename: Renate
authors.initials: R
authors.lastname: Scheibe
mesh_terms: D017360:Arabidopsis / Q000201:enzymology / Q000235:genetics / Q000378:metabolism*; D050538:Malate Dehydrogenase (NADP+) / Q000235:genetics*; D010084:Oxidation-Reduction; D018384:Oxidative Stress / Q000235:genetics / Q000502:physiology*; D010788:Photosynthesis / Q000235:genetics / Q000502:physiology; D030821:Plants, Genetically Modified / Q000201:enzymology / Q000235:genetics / Q000378:metabolism*
chemical_list: D050538:Malate Dehydrogenase (NADP+)