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Shevela D, Schröder WP, Messinger J. Measurements of Oxygen Evolution in Photosynthesis. Methods Mol Biol 2024; 2790:133-148. [PMID: 38649570 DOI: 10.1007/978-1-0716-3790-6_8] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 04/25/2024]
Abstract
This chapter compares two different techniques for monitoring photosynthetic O2 production; the wide-spread Clark-type O2 electrode and the more sophisticated membrane inlet mass spectrometry (MIMS) technique. We describe how a simple membrane inlet for MIMS can be made out of a commercial Clark-type cell and outline the advantages and drawbacks of the two techniques to guide researchers in deciding which method to use. Protocols and examples are given for measuring O2 evolution rates and for determining the number of chlorophyll molecules per active photosystem II reaction center.
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Affiliation(s)
| | | | - Johannes Messinger
- Department of Chemistry, Umeå University, Umeå, Sweden.
- Department of Chemistry - Ångström, Uppsala University, Uppsala, Sweden.
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Amthor JS. ATP yield of plant respiration: potential, actual and unknown. ANNALS OF BOTANY 2023; 132:133-162. [PMID: 37409716 PMCID: PMC10550282 DOI: 10.1093/aob/mcad075] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/31/2023] [Accepted: 07/04/2023] [Indexed: 07/07/2023]
Abstract
BACKGROUND AND AIMS The ATP yield of plant respiration (ATP/hexose unit respired) quantitatively links active heterotrophic processes with substrate consumption. Despite its importance, plant respiratory ATP yield is uncertain. The aim here was to integrate current knowledge of cellular mechanisms with inferences required to fill knowledge gaps to generate a contemporary estimate of respiratory ATP yield and identify important unknowns. METHOD A numerical balance sheet model combining respiratory carbon metabolism and electron transport pathways with uses of the resulting transmembrane electrochemical proton gradient was created and parameterized for healthy, non-photosynthesizing plant cells catabolizing sucrose or starch to produce cytosolic ATP. KEY RESULTS Mechanistically, the number of c subunits in the mitochondrial ATP synthase Fo sector c-ring, which is unquantified in plants, affects ATP yield. A value of 10 was (justifiably) used in the model, in which case respiration of sucrose potentially yields about 27.5 ATP/hexose (0.5 ATP/hexose more from starch). Actual ATP yield often will be smaller than its potential due to bypasses of energy-conserving reactions in the respiratory chain, even in unstressed plants. Notably, all else being optimal, if 25 % of respiratory O2 uptake is via the alternative oxidase - a typically observed fraction - ATP yield falls 15 % below its potential. CONCLUSIONS Plant respiratory ATP yield is smaller than often assumed (certainly less than older textbook values of 36-38 ATP/hexose) leading to underestimation of active-process substrate requirements. This hinders understanding of ecological/evolutionary trade-offs between competing active processes and assessments of crop growth gains possible through bioengineering of processes that consume ATP. Determining the plant mitochondrial ATP synthase c-ring size, the degree of any minimally required (useful) bypasses of energy-conserving reactions in the respiratory chain, and the magnitude of any 'leaks' in the inner mitochondrial membrane are key research needs.
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Affiliation(s)
- J S Amthor
- Center for Ecosystem Science and Society and Department of Biological Sciences, Northern Arizona University, Flagstaff, AZ 86011, USA
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Garcia A, Gaju O, Bowerman AF, Buck SA, Evans JR, Furbank RT, Gilliham M, Millar AH, Pogson BJ, Reynolds MP, Ruan Y, Taylor NL, Tyerman SD, Atkin OK. Enhancing crop yields through improvements in the efficiency of photosynthesis and respiration. THE NEW PHYTOLOGIST 2023; 237:60-77. [PMID: 36251512 PMCID: PMC10100352 DOI: 10.1111/nph.18545] [Citation(s) in RCA: 10] [Impact Index Per Article: 10.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/25/2022] [Accepted: 09/15/2022] [Indexed: 06/06/2023]
Abstract
The rate with which crop yields per hectare increase each year is plateauing at the same time that human population growth and other factors increase food demand. Increasing yield potential (Y p ) of crops is vital to address these challenges. In this review, we explore a component ofY p that has yet to be optimised - that being improvements in the efficiency with which light energy is converted into biomass (ε c ) via modifications to CO2 fixed per unit quantum of light (α), efficiency of respiratory ATP production (ε prod ) and efficiency of ATP use (ε use ). For α, targets include changes in photoprotective machinery, ribulose bisphosphate carboxylase/oxygenase kinetics and photorespiratory pathways. There is also potential forε prod to be increased via targeted changes to the expression of the alternative oxidase and mitochondrial uncoupling pathways. Similarly, there are possibilities to improveε use via changes to the ATP costs of phloem loading, nutrient uptake, futile cycles and/or protein/membrane turnover. Recently developed high-throughput measurements of respiration can serve as a proxy for the cumulative energy cost of these processes. There are thus exciting opportunities to use our growing knowledge of factors influencing the efficiency of photosynthesis and respiration to create a step-change in yield potential of globally important crops.
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Affiliation(s)
- Andres Garcia
- ARC Centre of Excellence in Plant Energy Biology, Research School of BiologyThe Australian National UniversityCanberraACT2601Australia
- Division of Plant Sciences, Research School of BiologyAustralian National UniversityCanberraACT2601Australia
| | - Oorbessy Gaju
- ARC Centre of Excellence in Plant Energy Biology, Research School of BiologyThe Australian National UniversityCanberraACT2601Australia
- College of Science, Lincoln Institute for Agri‐Food TechnologyUniversity of LincolnLincolnshireLN2 2LGUK
| | - Andrew F. Bowerman
- ARC Centre of Excellence in Plant Energy Biology, Research School of BiologyThe Australian National UniversityCanberraACT2601Australia
- Division of Plant Sciences, Research School of BiologyAustralian National UniversityCanberraACT2601Australia
| | - Sally A. Buck
- ARC Centre of Excellence in Plant Energy Biology, Research School of BiologyThe Australian National UniversityCanberraACT2601Australia
- Division of Plant Sciences, Research School of BiologyAustralian National UniversityCanberraACT2601Australia
| | - John R. Evans
- Division of Plant Sciences, Research School of BiologyAustralian National UniversityCanberraACT2601Australia
- ARC Centre of Excellence for Translational Photosynthesis, Research School of BiologyThe Australian National UniversityCanberraACT2601Australia
| | - Robert T. Furbank
- Division of Plant Sciences, Research School of BiologyAustralian National UniversityCanberraACT2601Australia
- ARC Centre of Excellence for Translational Photosynthesis, Research School of BiologyThe Australian National UniversityCanberraACT2601Australia
| | - Matthew Gilliham
- ARC Centre of Excellence in Plant Energy Biology, School of Agriculture, Food and Wine & Waite Research InstituteUniversity of AdelaideGlen OsmondSA5064Australia
| | - A. Harvey Millar
- ARC Centre of Excellence in Plant Energy Biology, School of Molecular Sciences & Institute of AgricultureThe University of Western AustraliaCrawleyWA6009Australia
| | - Barry J. Pogson
- ARC Centre of Excellence in Plant Energy Biology, Research School of BiologyThe Australian National UniversityCanberraACT2601Australia
- Division of Plant Sciences, Research School of BiologyAustralian National UniversityCanberraACT2601Australia
| | - Matthew P. Reynolds
- International Maize and Wheat Improvement Center (CIMMYT)Km. 45, Carretera Mexico, El BatanTexcoco56237Mexico
| | - Yong‐Ling Ruan
- Division of Plant Sciences, Research School of BiologyAustralian National UniversityCanberraACT2601Australia
| | - Nicolas L. Taylor
- ARC Centre of Excellence in Plant Energy Biology, School of Molecular Sciences & Institute of AgricultureThe University of Western AustraliaCrawleyWA6009Australia
| | - Stephen D. Tyerman
- ARC Centre of Excellence in Plant Energy Biology, School of Agriculture, Food and Wine & Waite Research InstituteUniversity of AdelaideGlen OsmondSA5064Australia
| | - Owen K. Atkin
- ARC Centre of Excellence in Plant Energy Biology, Research School of BiologyThe Australian National UniversityCanberraACT2601Australia
- Division of Plant Sciences, Research School of BiologyAustralian National UniversityCanberraACT2601Australia
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Managing argon interference during measurements of 18O/ 16O ratios in O 2 by continuous-flow isotope ratio mass spectrometry. Anal Bioanal Chem 2022; 414:6177-6186. [PMID: 35841416 PMCID: PMC9314310 DOI: 10.1007/s00216-022-04184-3] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/08/2022] [Revised: 06/08/2022] [Accepted: 06/17/2022] [Indexed: 11/08/2022]
Abstract
Abstract Monitoring changes in stable oxygen isotope ratios in molecular oxygen allows for studying many fundamental processes in bio(geo)chemistry and environmental sciences. While the measurement of \documentclass[12pt]{minimal}
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\begin{document}$$^{18}$$\end{document}18O/\documentclass[12pt]{minimal}
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\begin{document}$$\mathrm {O}_{2}$$\end{document}O2 in gaseous samples can be carried out conveniently and from extracting moderately small aqueous samples for analyses by continuous-flow isotope ratio mass spectrometry (CF-IRMS), oxygen isotope signatures, \documentclass[12pt]{minimal}
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\begin{document}$$\updelta ^{18}$$\end{document}δ18O, could be overestimated by more than 6\documentclass[12pt]{minimal}
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\begin{document}$$\permille$$\end{document}‱ because of interferences from argon in air. Here, we systematically evaluated the extent of such Ar interferences on \documentclass[12pt]{minimal}
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\begin{document}$$\mathrm {O}_{2}$$\end{document}O2 for measurements by gas chromatography/IRMS and GasBench/IRMS and propose simple instrumental modifications for improved Ar and \documentclass[12pt]{minimal}
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\begin{document}$$\mathrm {O}_{2}$$\end{document}O2 separation as well as post-measurement correction procedures for obtaining accurate \documentclass[12pt]{minimal}
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\begin{document}$$\updelta ^{18}$$\end{document}δ18O. We subsequently evaluated the consequences of Ar interferences for the quantification of O isotope fractionation in terms of isotope enrichment factors, \documentclass[12pt]{minimal}
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\begin{document}$$\upepsilon _{\mathrm {O}}$$\end{document}ϵO, and \documentclass[12pt]{minimal}
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\begin{document}$$^{18}$$\end{document}18O kinetic isotope effects (\documentclass[12pt]{minimal}
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\begin{document}$$^{18}$$\end{document}18O KIEs) in samples where \documentclass[12pt]{minimal}
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\begin{document}$$\mathrm {O}_{2}$$\end{document}O2 is consumed and Ar:\documentclass[12pt]{minimal}
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\begin{document}$$\mathrm {O}_{2}$$\end{document}O2 ratios increase steadily and substantially over the course of a reaction. We show that the extent of O isotope fractionation is overestimated only slightly and that this effect is typically smaller than uncertainties originating from the precision of \documentclass[12pt]{minimal}
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\begin{document}$$\updelta ^{18}$$\end{document}δ18O measurements and experimental variability. Ar interferences can become more relevant and bias \documentclass[12pt]{minimal}
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\begin{document}$$\upepsilon _{\mathrm {O}}$$\end{document}ϵO values by more than \documentclass[12pt]{minimal}
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\begin{document}$$2\permille$$\end{document}2‱ in aqueous samples where fractional \documentclass[12pt]{minimal}
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\begin{document}$$\mathrm {O}_{2}$$\end{document}O2 conversion exceeds 90%. Practically, however, such samples would typically contain less than 25 \documentclass[12pt]{minimal}
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\begin{document}$$\mathrm {O}_{2}$$\end{document}O2 at ambient temperature, an amount that is close to the method detection limit of \documentclass[12pt]{minimal}
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\begin{document}$$^{16}$$\end{document}16O ratio measurement by CF-IRMS. Graphical abstract ![]()
Supplementary Information The online version contains supplementary material available at 10.1007/s00216-022-04184-3.
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Bathellier C, Yu LJ, Farquhar GD, Coote ML, Lorimer GH, Tcherkez G. Ribulose 1,5-bisphosphate carboxylase/oxygenase activates O 2 by electron transfer. Proc Natl Acad Sci U S A 2020; 117:24234-24242. [PMID: 32934141 PMCID: PMC7533879 DOI: 10.1073/pnas.2008824117] [Citation(s) in RCA: 17] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023] Open
Abstract
Ribulose 1,5-bisphosphate carboxylase/oxygenase (Rubisco) is the cornerstone of atmospheric CO2 fixation by the biosphere. It catalyzes the addition of CO2 onto enolized ribulose 1,5-bisphosphate (RuBP), producing 3-phosphoglycerate which is then converted to sugars. The major problem of this reaction is competitive O2 addition, which forms a phosphorylated product (2-phosphoglycolate) that must be recycled by a series of biochemical reactions (photorespiratory metabolism). However, the way the enzyme activates O2 is still unknown. Here, we used isotope effects (with 2H, 25Mg, and 18O) to monitor O2 activation and assess the influence of outer sphere atoms, in two Rubisco forms of contrasted O2/CO2 selectivity. Neither the Rubisco form nor the use of solvent D2O and deuterated RuBP changed the 16O/18O isotope effect of O2 addition, in clear contrast with the 12C/13C isotope effect of CO2 addition. Furthermore, substitution of light magnesium (24Mg) by heavy, nuclear magnetic 25Mg had no effect on O2 addition. Therefore, outer sphere protons have no influence on the reaction and direct radical chemistry (intersystem crossing with triplet O2) does not seem to be involved in O2 activation. Computations indicate that the reduction potential of enolized RuBP (near 0.49 V) is compatible with superoxide (O2•-) production, must be insensitive to deuteration, and yields a predicted 16O/18O isotope effect and energy barrier close to observed values. Overall, O2 undergoes single electron transfer to form short-lived superoxide, which then recombines to form a peroxide intermediate.
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Affiliation(s)
- Camille Bathellier
- Elementar France, Spectrométrie de Masse Isotopique, 69428 Lyon Cedex 3, France
- Research School of Biology, ANU Joint College of Sciences, Australian National University, 2601 Canberra ACT, Australia
| | - Li-Juan Yu
- Australian Research Council Centre of Excellence for Electromaterials Science, Research School of Chemistry, ANU Joint College of Sciences, Australian National University, 2601 Canberra ACT, Australia
| | - Graham D Farquhar
- Research School of Biology, ANU Joint College of Sciences, Australian National University, 2601 Canberra ACT, Australia;
| | - Michelle L Coote
- Australian Research Council Centre of Excellence for Electromaterials Science, Research School of Chemistry, ANU Joint College of Sciences, Australian National University, 2601 Canberra ACT, Australia
| | - George H Lorimer
- Department of Chemistry and Biochemistry, University of Maryland, College Park, MD 20742
| | - Guillaume Tcherkez
- Research School of Biology, ANU Joint College of Sciences, Australian National University, 2601 Canberra ACT, Australia;
- Institut de Recherche en Horticulture et Semences, Institut National de Recherche pour l'Agriculture, l'Alimentation et l'Environnement (INRAe), Université d'Angers, 49070 Beaucouzé, France
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6
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Burlacot A, Burlacot F, Li-Beisson Y, Peltier G. Membrane Inlet Mass Spectrometry: A Powerful Tool for Algal Research. FRONTIERS IN PLANT SCIENCE 2020; 11:1302. [PMID: 33013952 PMCID: PMC7500362 DOI: 10.3389/fpls.2020.01302] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/18/2020] [Accepted: 08/11/2020] [Indexed: 05/15/2023]
Abstract
Since the first great oxygenation event, photosynthetic microorganisms have continuously shaped the Earth's atmosphere. Studying biological mechanisms involved in the interaction between microalgae and cyanobacteria with the Earth's atmosphere requires the monitoring of gas exchange. Membrane inlet mass spectrometry (MIMS) has been developed in the early 1960s to study gas exchange mechanisms of photosynthetic cells. It has since played an important role in investigating various cellular processes that involve gaseous compounds (O2, CO2, NO, or H2) and in characterizing enzymatic activities in vitro or in vivo. With the development of affordable mass spectrometers, MIMS is gaining wide popularity and is now used by an increasing number of laboratories. However, it still requires an important theory and practical considerations to be used. Here, we provide a practical guide describing the current technical basis of a MIMS setup and the general principles of data processing. We further review how MIMS can be used to study various aspects of algal research and discuss how MIMS will be useful in addressing future scientific challenges.
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Measurements of Electron Partitioning Between Cytochrome and Alternative Oxidase Pathways in Plant Tissues. Methods Mol Biol 2018; 1670:203-217. [PMID: 28871545 DOI: 10.1007/978-1-4939-7292-0_17] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 04/27/2023]
Abstract
Plant respiration is characterized by the existence of the alternative oxidase pathway (AOP) that competes with cytochrome oxidase pathway (COP) for the electrons of the ubiquinone pool of the mitochondrial electron transport chain, thus reducing ATP synthesis. The oxygen (O2) isotope fractionation technique is the only available to determine the electron partitioning between the two pathways and their in vivo activities in plant tissues. In this chapter, the basis of the O2 isotope fractionation technique and its derived calculations are carefully explained together with a detailed description of the dual-inlet isotope ratio mass spectrometry (DI-IRMS) system and the protocol developed at the University of Balearic Islands. The key advantages of the DI-IRMS over other systems are highlighted as well as the potential problems of this technique. Among these problems, those associated with leakage, diffusion, and inhibitor treatments are noted and solutions to prevent, detect, and repair these problems are detailed.
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Del-Saz NF, Ribas-Carbo M, McDonald AE, Lambers H, Fernie AR, Florez-Sarasa I. An In Vivo Perspective of the Role(s) of the Alternative Oxidase Pathway. TRENDS IN PLANT SCIENCE 2018; 23:206-219. [PMID: 29269217 DOI: 10.1016/j.tplants.2017.11.006] [Citation(s) in RCA: 93] [Impact Index Per Article: 15.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/26/2017] [Revised: 10/18/2017] [Accepted: 11/15/2017] [Indexed: 05/02/2023]
Abstract
Despite intense research on the in vitro characterization of regulatory factors modulating the alternative oxidase (AOX) pathway, the regulation of its activity in vivo is still not fully understood. Advances concerning in vivo regulation of AOX based on the oxygen-isotope fractionation technique are reviewed, and regulatory factors that merit future research are highlighted. In addition, we review and discuss the main biological functions assigned to the plant AOX, and suggest future experiments involving in vivo activity measurements to test different hypothesized physiological roles.
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Affiliation(s)
- Néstor Fernández Del-Saz
- Grup de Recerca en Biologia de les Plantes en Condicions Mediterranies, Universitat de les Illes Balears, Carretera de Valldemossa Km 7.5, 07122 Palma de Mallorca, Spain
| | - Miquel Ribas-Carbo
- Grup de Recerca en Biologia de les Plantes en Condicions Mediterranies, Universitat de les Illes Balears, Carretera de Valldemossa Km 7.5, 07122 Palma de Mallorca, Spain
| | - Allison E McDonald
- Department of Biology, Wilfrid Laurier University, Science Building, 75 University Avenue West, Waterloo, ON N2L 3C5, Canada
| | - Hans Lambers
- School of Biological Sciences, University of Western Australia, 35 Stirling Highway, Crawley (Perth), Western Australia 6009, Australia
| | - Alisdair R Fernie
- Max-Planck-Institut für Molekulare Pflanzenphysiologie, Am Mühlenberg 1, 14476 Potsdam-Golm, Germany
| | - Igor Florez-Sarasa
- Max-Planck-Institut für Molekulare Pflanzenphysiologie, Am Mühlenberg 1, 14476 Potsdam-Golm, Germany.
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9
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Lyu W, Selinski J, Li L, Day DA, Murcha MW, Whelan J, Wang Y. Isolation and Respiratory Measurements of Mitochondria from Arabidopsis thaliana. J Vis Exp 2018. [PMID: 29364229 DOI: 10.3791/56627] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/26/2022] Open
Abstract
Mitochondria are essential organelles involved in numerous metabolic pathways in plants, most notably the production of adenosine triphosphate (ATP) from the oxidation of reduced compounds such as nicotinamide adenine dinucleotide (NADH) and flavin adenine dinucleotide (FADH2). The complete annotation of the Arabidopsis thaliana genome has established it as the most widely used plant model system, and thus the need to purify mitochondria from a variety of organs (leaf, root, or flower) is necessary to fully utilize the tools that are now available for Arabidopsis to study mitochondrial biology. Mitochondria are isolated by homogenization of the tissue using a variety of approaches, followed by a series of differential centrifugation steps producing a crude mitochondrial pellet that is further purified using continuous colloidal density gradient centrifugation. The colloidal density material is subsequently removed by multiple centrifugation steps. Starting from 100 g of fresh leaf tissue, 2 - 3 mg of mitochondria can be routinely obtained. Respiratory experiments on these mitochondria display typical rates of 100 - 250 nmol O2 min-1 mg total mitochondrial protein-1 (NADH-dependent rate) with the ability to use various substrates and inhibitors to determine which substrates are being oxidized and the capacity of the alternative and cytochrome terminal oxidases. This protocol describes an isolation method of mitochondria from Arabidopsis thaliana leaves using continuous colloidal density gradients and an efficient respiratory measurements of purified plant mitochondria.
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Affiliation(s)
- Wenhui Lyu
- ARC Centre of Excellence in Plant Energy Biology, Department of Animal, Plant and Soil Science, School of Life Science, La Trobe University
| | - Jennifer Selinski
- ARC Centre of Excellence in Plant Energy Biology, Department of Animal, Plant and Soil Science, School of Life Science, La Trobe University;
| | - Lu Li
- ARC Centre of Excellence in Plant Energy Biology, Department of Animal, Plant and Soil Science, School of Life Science, La Trobe University
| | - David A Day
- School of Biological Sciences, Flinders University
| | - Monika W Murcha
- ARC Centre of Excellence in Plant Energy Biology, University of Western Australia
| | - James Whelan
- ARC Centre of Excellence in Plant Energy Biology, Department of Animal, Plant and Soil Science, School of Life Science, La Trobe University
| | - Yan Wang
- ARC Centre of Excellence in Plant Energy Biology, Department of Animal, Plant and Soil Science, School of Life Science, La Trobe University
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Abstract
This chapter compares two different techniques for monitoring photosynthetic O2 production: the widespread Clark-type O2 electrode and the more sophisticated membrane inlet mass spectrometry (MIMS) technique. We describe how a simple membrane inlet for MIMS can be made out of a commercial Clark-type cell, and outline the advantages and drawbacks of the two techniques to guide researchers in deciding which method to use. Protocols and examples are given for measuring O2 evolution rates and for determining the number of chlorophyll molecules per active photosystem II reaction center.
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Affiliation(s)
| | | | - Johannes Messinger
- Department of Chemistry, Umeå University, Umeå, Sweden.
- Department of Chemistry - Ångström Laboratory, Uppsala University, Uppsala, Sweden.
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Pati SG, Bolotin J, Brennwald MS, Kohler HPE, Werner RA, Hofstetter TB. Measurement of oxygen isotope ratios ((18)O/(16)O) of aqueous O2 in small samples by gas chromatography/isotope ratio mass spectrometry. RAPID COMMUNICATIONS IN MASS SPECTROMETRY : RCM 2016; 30:684-690. [PMID: 26864520 DOI: 10.1002/rcm.7481] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/19/2015] [Revised: 12/11/2015] [Accepted: 12/12/2015] [Indexed: 06/05/2023]
Abstract
RATIONALE Oxygen isotope fractionation of molecular O2 is an important process for the study of aerobic metabolism, photosynthesis, and formation of reactive oxygen species. The latter is of particular interest for investigating the mechanism of enzyme-catalyzed reactions, such as the oxygenation of organic pollutants, which is an important detoxification mechanism. METHODS We developed a simple method to measure the δ(18) O values of dissolved O2 in small samples using automated split injection for gas chromatography coupled to isotope ratio mass spectrometry (GC/IRMS). After creating a N2 headspace, the dissolved O2 partitions from aqueous solution to the headspace, from which it can be injected into the gas chromatograph. RESULTS In aqueous samples of 10 mL and in diluted air samples, we quantified the δ(18) O values at O2 concentrations of 16 μM and 86 μM, respectively. The chromatographic separation of O2 and N2 with a molecular sieve column made it possible to use N2 as the headspace gas for the extraction of dissolved O2 from water. We were therefore able to apply a rigorous δ(18) O blank correction for the quantification of (18) O/(16) O ratios in 20 nmol of injected O2 . CONCLUSIONS The successful quantification of (18) O-kinetic isotope effects associated with enzymatic and chemical reduction of dissolved O2 illustrates how the proposed method can be applied for studying enzymatic O2 activation mechanisms in a variety of (bio)chemical processes.
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Affiliation(s)
- Sarah G Pati
- Eawag, Swiss Federal Institute of Aquatic Science and Technology, CH-8600, Dübendorf, Switzerland
- Institute of Biogeochemistry and Pollutant Dynamics (IBP), ETH Zürich, CH-8092, Zürich, Switzerland
| | - Jakov Bolotin
- Eawag, Swiss Federal Institute of Aquatic Science and Technology, CH-8600, Dübendorf, Switzerland
| | - Matthias S Brennwald
- Eawag, Swiss Federal Institute of Aquatic Science and Technology, CH-8600, Dübendorf, Switzerland
| | - Hans-Peter E Kohler
- Eawag, Swiss Federal Institute of Aquatic Science and Technology, CH-8600, Dübendorf, Switzerland
- Institute of Biogeochemistry and Pollutant Dynamics (IBP), ETH Zürich, CH-8092, Zürich, Switzerland
| | - Roland A Werner
- Institute of Agricultural Sciences, ETH Zürich, CH-8092, Zürich, Switzerland
| | - Thomas B Hofstetter
- Eawag, Swiss Federal Institute of Aquatic Science and Technology, CH-8600, Dübendorf, Switzerland
- Institute of Biogeochemistry and Pollutant Dynamics (IBP), ETH Zürich, CH-8092, Zürich, Switzerland
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