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.
Highlights
Mitochondrial malate dehydrogenase catalyses the interconversion of malate and oxaloacetate (OAA) in the tricarboxylic acid (TCA) cycle and its activity is important for redox control of the mitochondrial matrix, through which it may participate in regulation of the TCA cycle turnover (Nunes-Nesi et al, 2005; Tomaz et al, 2010)
The metabolic profiles were analysed by gas- and liquid- chromatography coupled to mass spectrometry to investigate the metabolic adjustments between wild type and mmdh1
Our results indicate that adequate Mitochondrial malate dehydrogenase (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
Summary
Mitochondrial malate dehydrogenase (mMDH) catalyses the interconversion of malate and oxaloacetate (OAA) in the tricarboxylic acid (TCA) cycle and its activity is important for redox control of the mitochondrial matrix, through which it may participate in regulation of the TCA cycle turnover (Nunes-Nesi et al, 2005; Tomaz et al, 2010). Its activity is closely linked to malate/OAA exchange across the mitochondrial inner membrane. This process may be especially important for shuttling reductants between mitochondria and peroxisomes during photorespiration; in which equimolar amounts of NADH are produced during glycine oxidation in mitochondria and consumed in the reduction of hydroxypyruvate to glycerate in peroxisomes (Bauwe et al, 2010). Tomaz et al (2010) found that the double mutant mmdh1mmdh had a dramatically reduced growth rate, which could be, at least partly, related to disturbances in photorespiratory metabolism. Mmdh and mmdh, both had a reduced mMDH activity (~60% and ~40% reductions, respectively), neither displayed an apparent growth phenotype when grown under a controlled environment in air. A slight perturbation in the CO2 response curve was recorded in mmdh, suggesting that photorespiration might be affected in these plants (Tomaz et al, 2010)
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
