title: Reduced mitochondrial malate dehydrogenase activity has a strong effect on photorespiratory metabolism as revealed by 13C labelling.
abstract: Mitochondrial malate dehydrogenase (mMDH) catalyses the interconversion of malate and oxaloacetate (OAA) in the tricarboxylic acid (TCA) cycle. Its activity is important for redox control of the mitochondrial matrix, through which it may participate in regulation of TCA cycle turnover. In Arabidopsis, there are two isoforms of mMDH. Here, we investigated to which extent the lack of the major isoform, mMDH1 accounting for about 60% of the activity, affected leaf metabolism. In air, rosettes of mmdh1 plants were only slightly smaller than wild type plants although the fresh weight was decreased by about 50%. In low CO2 the difference was much bigger, with mutant plants accumulating only 14% of fresh weight as compared to wild type. To investigate the metabolic background to the differences in growth, we developed a (13)CO2 labelling method, using a custom-built chamber that enabled simultaneous treatment of sets of plants under controlled conditions. The metabolic profiles were analysed by gas- and liquid- chromatography coupled to mass spectrometry to investigate the metabolic adjustments between wild type and mmdh1 The genotypes responded similarly to high CO2 treatment both with respect to metabolite pools and (13)C incorporation during a 2-h treatment. However, under low CO2 several metabolites differed between the two genotypes and, interestingly most of these were closely associated with photorespiration. We found that while the glycine/serine ratio increased, a concomitant altered glutamine/glutamate/α-ketoglutarate relation occurred. Taken together, our results indicate that adequate mMDH activity is essential to shuttle reductants out from the mitochondria to support the photorespiratory flux, and strengthen the idea that photorespiration is tightly intertwined with peripheral metabolic reactions.
authors.affiliation: Umeå Plant Science Centre, Department of Forest Genetics and Plant Physiology, Swedish University of Agricultural Sciences , SE-901 83 Umeå, Sweden.
authors.forename: Pernilla
authors.initials: P
authors.lastname: Lindén
authors.affiliation: Umeå Plant Science Centre, Department of Plant Physiology, Umeå University, SE-901 87 Umeå, Sweden.
authors.forename: Olivier
authors.initials: O
authors.lastname: Keech
authors.affiliation: Swedish Metabolomics Centre, Department of Molecular Biology, Umeå University, SE-901 87 Umeå, Sweden.
authors.forename: Hans
authors.initials: H
authors.lastname: Stenlund
authors.affiliation: Umeå Plant Science Centre, Department of Plant Physiology, Umeå University, SE-901 87 Umeå, Sweden thomas.moritz@slu.se per.gardestrom@umu.se.
authors.forename: Per
authors.initials: P
authors.lastname: Gardeström
authors.affiliation: Umeå Plant Science Centre, Department of Forest Genetics and Plant Physiology, Swedish University of Agricultural Sciences , SE-901 83 Umeå, Sweden thomas.moritz@slu.se per.gardestrom@umu.se.
authors.forename: Thomas
authors.initials: T
authors.lastname: Moritz
mesh_terms: D017360:Arabidopsis / Q000378:metabolism / Q000502:physiology; D002247:Carbon Isotopes / Q000378:metabolism; D008401:Gas Chromatography-Mass Spectrometry; D008291:Malate Dehydrogenase / Q000378:metabolism* / Q000502:physiology; D008928:Mitochondria / Q000201:enzymology / Q000378:metabolism*; D010084:Oxidation-Reduction; D010788:Photosynthesis / Q000502:physiology*
chemical_list: D002247:Carbon Isotopes; D008291:Malate Dehydrogenase
keywords: Heavy isotope labelling; mass spectrometry; mitochondrial malate dehydrogenase; photorespiration; primary carbon metabolism; redox balance.