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Leverett A, Kromdijk J. The long and tortuous path towards improving photosynthesis by engineering elevated mesophyll conductance. PLANT, CELL & ENVIRONMENT 2024; 47:3411-3427. [PMID: 38804598 DOI: 10.1111/pce.14940] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/14/2023] [Revised: 03/13/2024] [Accepted: 04/29/2024] [Indexed: 05/29/2024]
Abstract
The growing demand for global food production is likely to be a defining issue facing humanity over the next 50 years. To tackle this challenge, there is a desire to bioengineer crops with higher photosynthetic efficiencies, to increase yields. Recently, there has been a growing interest in engineering leaves with higher mesophyll conductance (gm), which would allow CO2 to move more efficiently from the substomatal cavities to the chloroplast stroma. However, if crop yield gains are to be realised through this approach, it is essential that the methodological limitations associated with estimating gm are fully appreciated. In this review, we summarise these limitations, and outline the uncertainties and assumptions that can affect the final estimation of gm. Furthermore, we critically assess the predicted quantitative effect that elevating gm will have on assimilation rates in crop species. We highlight the need for more theoretical modelling to determine whether altering gm is truly a viable route to improve crop performance. Finally, we offer suggestions to guide future research on gm, which will help mitigate the uncertainty inherently associated with estimating this parameter.
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Affiliation(s)
- Alistair Leverett
- Department of Plant Sciences, University of Cambridge, Cambridge, UK
| | - Johannes Kromdijk
- Department of Plant Sciences, University of Cambridge, Cambridge, UK
- Institute for Genomic Biology, University of Illinois at Urbana-Champaign, Urbana, Illinois, USA
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2
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Janová J, Kubásek J, Grams TEE, Zeisler-Diehl V, Schreiber L, Šantrůček J. Effect of light-induced changes in leaf anatomy on intercellular and cellular components of mesophyll resistance for CO 2 in Fagus sylvatica. PLANT BIOLOGY (STUTTGART, GERMANY) 2024; 26:842-854. [PMID: 38743618 DOI: 10.1111/plb.13655] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/25/2024] [Accepted: 04/15/2024] [Indexed: 05/16/2024]
Abstract
Mesophyll resistance for CO2 diffusion (rm) is one of the main limitations for photosynthesis and plant growth. Breeding new varieties with lower rm requires knowledge of its distinct components. We tested new method for estimating the relative drawdowns of CO2 concentration (c) across hypostomatous leaves of Fagus sylvatica. This technique yields values of the ratio of the internal CO2 concentrations at the adaxial and abaxial leaf side, cd/cb, the drawdown in the intercellular air space (IAS), and intracellular drawdown between IAS and chloroplast stroma, cc/cbd. The method is based on carbon isotope composition of leaf dry matter and epicuticular wax isolated from upper and lower leaf sides. We investigated leaves from tree-canopy profile to analyse the effects of light and leaf anatomy on the drawdowns and partitioning of rm into its inter- (rIAS) and intracellular (rliq) components. Validity of the new method was tested by independent measurements of rm using conventional isotopic and gas exchange techniques. 73% of investigated leaves had adaxial epicuticular wax enriched in 13C compared to abaxial wax (by 0.50‰ on average), yielding 0.98 and 0.70 for average of cd/cb and cc/cbd, respectively. The rIAS to rliq proportion were 5.5:94.5% in sun-exposed and 14.8:85.2% in shaded leaves. cc dropped to less than half of the atmospheric value in the sunlit and to about two-thirds of it in shaded leaves. This method shows that rIAS is minor but not negligible part of rm and reflects leaf anatomy traits, i.e. leaf mass per area and thickness.
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Affiliation(s)
- J Janová
- Faculty of Science, University of South Bohemia, České Budějovice, Czech Republic
| | - J Kubásek
- Faculty of Science, University of South Bohemia, České Budějovice, Czech Republic
| | - T E E Grams
- Ecophysiology of Plants, Technical University of Munich, Freising, Germany
| | - V Zeisler-Diehl
- Institute of Cellular and Molecular Botany, University of Bonn, Bonn, Germany
| | - L Schreiber
- Institute of Cellular and Molecular Botany, University of Bonn, Bonn, Germany
| | - J Šantrůček
- Faculty of Science, University of South Bohemia, České Budějovice, Czech Republic
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3
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Tholen D. GasanalyzeR: advancing reproducible research using a new R package for photosynthesis data workflows. AOB PLANTS 2024; 16:plae035. [PMID: 39040093 PMCID: PMC11261163 DOI: 10.1093/aobpla/plae035] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 04/14/2024] [Accepted: 06/18/2024] [Indexed: 07/24/2024]
Abstract
The analysis of photosynthetic traits has become an integral part of plant (eco-)physiology. Many of these characteristics are not directly measured, but calculated from combinations of several, more direct, measurements. The calculations of such derived variables are based on underlying physical models and may use additional constants or assumed values. Commercially available gas-exchange instruments typically report such derived variables, but the available implementations use different definitions and assumptions. Moreover, no software is currently available to allow a fully scripted and reproducible workflow that includes importing data, pre-processing and recalculating derived quantities. The R package gasanalyzer aims to address these issues by providing methods to import data from different instruments, by translating photosynthetic variables to a standardized nomenclature, and by optionally recalculating derived quantities using standardized equations. In addition, the package facilitates performing sensitivity analyses on variables or assumptions used in the calculations to allow researchers to better assess the robustness of the results. The use of the package and how to perform sensitivity analyses are demonstrated using three different examples.
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Affiliation(s)
- Danny Tholen
- Department of Integrative Biology and Biodiversity Research, Institute of Botany, the University of Natural Resources and Life Sciences, Vienna, 1180 Vienna, Austria
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4
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Ubierna N, Holloway-Phillips MM, Wingate L, Ogée J, Busch FA, Farquhar GD. Using Carbon Stable Isotopes to Study C 3 and C 4 Photosynthesis: Models and Calculations. Methods Mol Biol 2024; 2790:163-211. [PMID: 38649572 DOI: 10.1007/978-1-0716-3790-6_10] [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
Stable carbon isotopes are a powerful tool to study photosynthesis. Initial applications consisted of determining isotope ratios of plant biomass using mass spectrometry. Subsequently, theoretical models relating C isotope values to gas exchange characteristics were introduced and tested against instantaneous online measurements of 13C photosynthetic discrimination. Beginning in the twenty-first century, laser absorption spectroscopes with sufficient precision for determining isotope mixing ratios became commercially available. This has allowed collection of large data sets at lower cost and with unprecedented temporal resolution. More data and accompanying knowledge have permitted refinement of 13C discrimination model equations, but often at the expense of increased model complexity and difficult parametrization. This chapter describes instantaneous online measurements of 13C photosynthetic discrimination, provides recommendations for experimental setup, and presents a thorough compilation of equations available to researchers. We update our previous 2018 version of this chapter by including recently improved descriptions of (photo)respiratory processes and associated fractionations. We discuss the capabilities and limitations of the diverse 13C discrimination model equations and provide guidance for selecting the model complexity needed for different applications.
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Affiliation(s)
- Nerea Ubierna
- Institut National de Recherche pour l'Agriculture, l'Alimentation et l'Environnement (INRAE), Unité Mixte de Recherche (UMR)1391 ISPA, Villenave D'Ornon, France
| | - Meisha-Marika Holloway-Phillips
- Research Unit of Forest Dynamics, Swiss Federal Institute for Forest, Snow and Landscape Research WSL, Birmendsorf, Switzerland
| | - Lisa Wingate
- Institut National de Recherche pour l'Agriculture, l'Alimentation et l'Environnement (INRAE), Unité Mixte de Recherche (UMR)1391 ISPA, Villenave D'Ornon, France
| | - Jérôme Ogée
- Institut National de Recherche pour l'Agriculture, l'Alimentation et l'Environnement (INRAE), Unité Mixte de Recherche (UMR)1391 ISPA, Villenave D'Ornon, France
| | - Florian A Busch
- School of Biosciences and The Birmingham Institute of Forest Research, University of Birmingham, Birmingham, UK
| | - Graham D Farquhar
- Research School of Biology, Australian National University, Canberra, ACT, Australia
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5
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Gregory LM, Roze LV, Walker BJ. Increased activity of core photorespiratory enzymes and CO 2 transfer conductances are associated with higher and more optimal photosynthetic rates under elevated temperatures in the extremophile Rhazya stricta. PLANT, CELL & ENVIRONMENT 2023; 46:3704-3720. [PMID: 37667571 DOI: 10.1111/pce.14711] [Citation(s) in RCA: 2] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/11/2022] [Revised: 06/26/2023] [Accepted: 08/23/2023] [Indexed: 09/06/2023]
Abstract
Increase photorespiration and optimising intrinsic water use efficiency are unique challenges to photosynthetic carbon fixation at elevated temperatures. To determine how plants can adapt to facilitate high rates of photorespiration at elevated temperatures while also maintaining water-use efficiency, we performed in-depth gas exchange and biochemical assays of the C3 extremophile, Rhazya stricta. These results demonstrate that R. stricta supports higher rates of photorespiration under elevated temperatures and that these higher rates of photorespiration correlate with increased activity of key photorespiratory enzymes; phosphoglycolate phosphatase and catalase. The increased photorespiratory enzyme activities may increase the overall capacity of photorespiration by reducing enzymatic bottlenecks and allowing minimal inhibitor accumulation under high photorespiratory rates. Additionally, we found the CO2 transfer conductances (stomatal and mesophyll) are re-allocated to increase the water-use efficiency in R. stricta but not necessarily the photosynthetic response to temperature. These results suggest important adaptive strategies in R. stricta that maintain photosynthetic rates under elevated temperatures with optimal water loss. The strategies found in R. stricta may inform breeding and engineering efforts in other C3 species to improve photosynthetic efficiency at high temperatures.
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Affiliation(s)
- Luke M Gregory
- Department of Energy-Plant Research Laboratory, Michigan State University, East Lansing, Michigan, USA
- Department of Plant Biology, Michigan State University, East Lansing, Michigan, USA
| | - Ludmila V Roze
- Department of Energy-Plant Research Laboratory, Michigan State University, East Lansing, Michigan, USA
| | - Berkley J Walker
- Department of Energy-Plant Research Laboratory, Michigan State University, East Lansing, Michigan, USA
- Department of Plant Biology, Michigan State University, East Lansing, Michigan, USA
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Tang Y, Schiestl-Aalto P, Lehmann MM, Saurer M, Sahlstedt E, Kolari P, Leppä K, Bäck J, Rinne-Garmston KT. Estimating intra-seasonal photosynthetic discrimination and water use efficiency using δ13C of leaf sucrose in Scots pine. JOURNAL OF EXPERIMENTAL BOTANY 2023; 74:321-335. [PMID: 36255219 PMCID: PMC9786842 DOI: 10.1093/jxb/erac413] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/25/2022] [Accepted: 10/17/2022] [Indexed: 05/31/2023]
Abstract
Sucrose has a unique role in recording environmental and physiological signals during photosynthesis in its carbon isotope composition (δ13C) and transport of the signal to tree rings. Yet, instead of sucrose, total organic matter (TOM) or water-soluble carbohydrates (WSC) are typically analysed in studies that follow δ13C signals within trees. To study how the choice of organic material may bias the interpretation of δ13C records, we used mature field-grown Scots pine (Pinus sylvestris) to compare for the first time δ13C of different leaf carbon pools with δ13C of assimilates estimated by a chamber-Picarro system (δ13CA_Picarro), and a photosynthetic discrimination model (δ13CA_model). Compared with sucrose, the other tested carbon pools, such as TOM and WSC, poorly recorded the seasonal trends or absolute values of δ13CA_Picarro and δ13CA_model. Consequently, in comparison with the other carbon pools, sucrose δ13C was superior for reconstructing changes in intrinsic water use efficiency (iWUE), agreeing in both absolute values and intra-seasonal variations with iWUE estimated from gas exchange. Thus, deriving iWUE and environmental signals from δ13C of bulk organic matter can lead to misinterpretation. Our findings underscore the advantage of using sucrose δ13C to understand plant physiological responses in depth.
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Affiliation(s)
| | - Paulina Schiestl-Aalto
- Institute for Atmospheric and Earth System Research (INAR)/Physics, Faculty of Science, University of Helsinki, P.O. Box 68, 00014, Helsinki, Finland
| | - Marco M Lehmann
- Forest Dynamics, Swiss Federal Institute for Forest, Snow and Landscape Research (WSL), Zürcherstrasse 111, 8903, Birmensdorf, Switzerland
| | - Matthias Saurer
- Forest Dynamics, Swiss Federal Institute for Forest, Snow and Landscape Research (WSL), Zürcherstrasse 111, 8903, Birmensdorf, Switzerland
| | - Elina Sahlstedt
- Bioeconomy and Environment Unit, Natural Resources Institute Finland (Luke), Latokartanonkaari 9, 00790, Helsinki, Finland
| | - Pasi Kolari
- Institute for Atmospheric and Earth System Research (INAR)/Physics, Faculty of Science, University of Helsinki, P.O. Box 68, 00014, Helsinki, Finland
| | - Kersti Leppä
- Bioeconomy and Environment Unit, Natural Resources Institute Finland (Luke), Latokartanonkaari 9, 00790, Helsinki, Finland
| | - Jaana Bäck
- Institute for Atmospheric and Earth System Research (INAR)/Forest Sciences, Faculty of Agriculture and Forestry, University of Helsinki, P.O. Box 27, 00014, Helsinki, Finland
| | - Katja T Rinne-Garmston
- Bioeconomy and Environment Unit, Natural Resources Institute Finland (Luke), Latokartanonkaari 9, 00790, Helsinki, Finland
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7
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Wilkes EB, Sessions AL, Zeichner SS, Dallas B, Schubert B, Jahren AH, Eiler JM. Position-specific carbon isotope analysis of serine by gas chromatography/Orbitrap mass spectrometry, and an application to plant metabolism. RAPID COMMUNICATIONS IN MASS SPECTROMETRY : RCM 2022; 36:e9347. [PMID: 35770334 DOI: 10.1002/rcm.9347] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/16/2021] [Revised: 06/22/2022] [Accepted: 06/23/2022] [Indexed: 06/15/2023]
Abstract
RATIONALE Position-specific 13 C/12 C ratios within amino acids remain largely unexplored in environmental samples due to methodological limitations. We hypothesized that natural-abundance isotope patterns in serine may serve as a proxy for plant metabolic fluxes including photorespiration. Here we describe an Orbitrap method optimized for the position-specific carbon isotope analysis of serine to test our hypothesis and discuss the generalizability of this method to other amino acids. METHODS Position-specific carbon isotope ratios of serine were measured using a Thermo Scientific™ Q Exactive™ GC Orbitrap™. Amino acids were hydrolyzed from Arabidopsis biomass, purified from potential matrix interferences, and derivatized alongside standards. Derivatized serine (N,O-bis(trifluoroacetyl)methyl ester) was isolated using gas chromatography, trapped in a reservoir, and purged into the electron ionization source over tens of minutes, producing fragment ions containing different combinations of atoms from the serine-derivative molecule. The 13 C/12 C ratios of fragments with monoisotopic masses of 110.0217, 138.0166, and 165.0037 Da were monitored in the mass analyzer and used to calculate position-specific δ13 C values relative to a working standard. RESULTS This methodology constrains position-specific δ13 C values for nanomole amounts of serine isolated from chemically complex mixtures. The δ13 C values of fragment ions of serine were characterized with ≤1‰ precisions, leading to propagated standard errors of 0.7-5‰ for each carbon position. Position-specific δ13 C values differed by up to ca 28 ± 5‰ between serine molecules hydrolyzed from plants grown under contrasting pCO2 , selected to promote different fluxes through photosynthesis and photorespiration. The method was validated using pure serine standards characterized offline. CONCLUSIONS This study presents the first Orbitrap-based measurements of natural-abundance, position-specific carbon isotope variation in an amino acid isolated from a biological matrix. We present a method for the precise characterization of isotope ratios in serine and propose applications probing metabolism in plants. We discuss the potential for extending these approaches to other amino acids, paving the way for novel applications.
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Affiliation(s)
- Elise B Wilkes
- Division of Geological and Planetary Sciences, Caltech, Pasadena, CA, USA
| | - Alex L Sessions
- Division of Geological and Planetary Sciences, Caltech, Pasadena, CA, USA
| | - Sarah S Zeichner
- Division of Geological and Planetary Sciences, Caltech, Pasadena, CA, USA
| | - Brooke Dallas
- Division of Geological and Planetary Sciences, Caltech, Pasadena, CA, USA
| | - Brian Schubert
- School of Geosciences, University of Louisiana at Lafayette, Lafayette, LA, USA
| | - A Hope Jahren
- Centre for Earth Evolution and Dynamics, University of Oslo, Oslo, Norway
| | - John M Eiler
- Division of Geological and Planetary Sciences, Caltech, Pasadena, CA, USA
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8
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Serk H, Nilsson MB, Figueira J, Wieloch T, Schleucher J. CO 2 fertilization of Sphagnum peat mosses is modulated by water table level and other environmental factors. PLANT, CELL & ENVIRONMENT 2021; 44:1756-1768. [PMID: 33751592 DOI: 10.1111/pce.14043] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/05/2020] [Revised: 03/04/2021] [Accepted: 03/04/2021] [Indexed: 06/12/2023]
Abstract
Sphagnum mosses account for most accumulated dead organic matter in peatlands. Therefore, understanding their responses to increasing atmospheric CO2 is needed for estimating peatland C balances under climate change. A key process is photorespiration: a major determinant of net photosynthetic C assimilation that depends on the CO2 to O2 ratio. We used climate chambers to investigate photorespiratory responses of Sphagnum fuscum hummocks to recent increases in atmospheric CO2 (from 280 to 400 ppm) under different water table, temperature, and light intensity levels. We tested the photorespiratory variability using a novel method based on deuterium isotopomers (D6S /D6R ratio) of photosynthetic glucose. The effect of elevated CO2 on photorespiration was highly dependent on water table. At low water table (-20 cm), elevated CO2 suppressed photorespiration relative to C assimilation, thus substantially increasing the net primary production potential. In contrast, a high water table (~0 cm) favored photorespiration and abolished this CO2 effect. The response was further tested for Sphagnum majus lawns at typical water table levels (~0 and -7 cm), revealing no effect of CO2 under those conditions. Our results indicate that hummocks, which typically experience low water table levels, benefit from the 20th century's increase in atmospheric CO2 .
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Affiliation(s)
- Henrik Serk
- Department of Medical Biochemistry and Biophysics, Umeå University, Umeå, Sweden
- Department of Forest Ecology and Management, Swedish University of Agricultural Sciences, Umeå, Sweden
| | - Mats B Nilsson
- Department of Forest Ecology and Management, Swedish University of Agricultural Sciences, Umeå, Sweden
| | - João Figueira
- Department of Chemistry, Scilife Lab, Umeå University, Umeå, Sweden
| | - Thomas Wieloch
- Department of Medical Biochemistry and Biophysics, Umeå University, Umeå, Sweden
| | - Jürgen Schleucher
- Department of Medical Biochemistry and Biophysics, Umeå University, Umeå, Sweden
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9
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Ghiasi S, Lehmann MM, Badeck FW, Ghashghaie J, Hänsch R, Meinen R, Streb S, Hüdig M, Ruckle ME, Carrera DÁ, Siegwolf RTW, Buchmann N, Werner RA. Nitrate and ammonium differ in their impact on δ 13C of plant metabolites and respired CO 2 from tobacco leaves. ISOTOPES IN ENVIRONMENTAL AND HEALTH STUDIES 2021; 57:11-34. [PMID: 32885670 DOI: 10.1080/10256016.2020.1810683] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/10/2019] [Accepted: 07/15/2020] [Indexed: 06/11/2023]
Abstract
The carbon isotopic composition (δ13C) of foliage is often used as proxy for plant performance. However, the effect of N O 3 - vs. N H 4 + supply on δ13C of leaf metabolites and respired CO2 is largely unknown. We supplied tobacco plants with a gradient of N O 3 - to N H 4 + concentration ratios and determined gas exchange variables, concentrations and δ13C of tricarboxylic acid (TCA) cycle intermediates, δ13C of dark-respired CO2, and activities of key enzymes nitrate reductase, malic enzyme and phosphoenolpyruvate carboxylase. Net assimilation rate, dry biomass and concentrations of organic acids and starch decreased along the gradient. In contrast, respiration rates, concentrations of intercellular CO2, soluble sugars and amino acids increased. As N O 3 - decreased, activities of all measured enzymes decreased. δ13C of CO2 and organic acids closely co-varied and were more positive under N O 3 - supply, suggesting organic acids as potential substrates for respiration. Together with estimates of intra-molecular 13C enrichment in malate, we conclude that a change in the anaplerotic reaction of the TCA cycle possibly contributes to 13C enrichment in organic acids and respired CO2 under N O 3 - supply. Thus, the effect of N O 3 - vs. N H 4 + on δ13C is highly relevant, particularly if δ13C of leaf metabolites or respiration is used as proxy for plant performance.
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Affiliation(s)
- Shiva Ghiasi
- Department of Environmental Systems Science, ETH Zurich, Zurich, Switzerland
| | - Marco M Lehmann
- Forest Dynamics, Swiss Federal Institute for Forest, Snow and Landscape Research WSL, Birmensdorf, Switzerland
| | - Franz-W Badeck
- Council for Agricultural Research and Economics, Research Centre for Genomics and Bioinformatics (CREA-GB), Fiorenzuola d´Arda, Italy
| | - Jaleh Ghashghaie
- Laboratoire d'Ecologie Systématique Evolution (ESE), Université Paris-Sud, CNRS, AgroParisTech, Université Paris-Saclay, Orsay, France
| | - Robert Hänsch
- Institute of Plant Biology, Technische Universität Braunschweig, Braunschweig, Germany
- Center of Molecular Ecophysiology (CMEP), College of Resources and Environment, Southwest University, Chongqing, People's Republic of China
| | - Rieke Meinen
- Institute of Plant Biology, Technische Universität Braunschweig, Braunschweig, Germany
| | | | - Meike Hüdig
- Institute of Molecular Physiology and Biotechnology of Plants (IMBIO), University of Bonn, Bonn, Germany
| | - Michael E Ruckle
- Department of Environmental Systems Science, ETH Zurich, Zurich, Switzerland
| | - Dániel Á Carrera
- Department of Environmental Systems Science, ETH Zurich, Zurich, Switzerland
| | - Rolf T W Siegwolf
- Department of Environmental Systems Science, ETH Zurich, Zurich, Switzerland
- Forest Dynamics, Swiss Federal Institute for Forest, Snow and Landscape Research WSL, Birmensdorf, Switzerland
| | - Nina Buchmann
- Department of Environmental Systems Science, ETH Zurich, Zurich, Switzerland
| | - Roland A Werner
- Department of Environmental Systems Science, ETH Zurich, Zurich, Switzerland
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10
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Busch FA, Holloway-Phillips M, Stuart-Williams H, Farquhar GD. Revisiting carbon isotope discrimination in C 3 plants shows respiration rules when photosynthesis is low. NATURE PLANTS 2020; 6:245-258. [PMID: 32170287 DOI: 10.1038/s41477-020-0606-6] [Citation(s) in RCA: 41] [Impact Index Per Article: 10.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/19/2019] [Accepted: 01/23/2020] [Indexed: 05/12/2023]
Abstract
Stable isotopes are commonly used to study the diffusion of CO2 within photosynthetic plant tissues. The standard method used to interpret the observed preference for the lighter carbon isotope in C3 photosynthesis involves the model of Farquhar et al., which relates carbon isotope discrimination to physical and biochemical processes within the leaf. However, under many conditions the model returns unreasonable results for mesophyll conductance to CO2 diffusion (gm), especially when rates of photosynthesis are low. Here, we re-derive the carbon isotope discrimination model using modified assumptions related to the isotope effect of mitochondrial respiration. In particular, we treat the carbon pool associated with respiration as separate from the pool of primary assimilates. We experimentally test the model by comparing gm values measured with different CO2 source gases varying in their isotopic composition, and show that our new model returns matching gm values that are much more reasonable than those obtained with the previous model. We use our results to discuss CO2 diffusion properties within the mesophyll.
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Affiliation(s)
- Florian A Busch
- Research School of Biology and ARC Centre of Excellence for Translational Photosynthesis, Australian National University, Acton, Australian Capital Territory, Australia.
| | - Meisha Holloway-Phillips
- Research School of Biology and ARC Centre of Excellence for Translational Photosynthesis, Australian National University, Acton, Australian Capital Territory, Australia
- Department of Environmental Sciences, University of Basel, Basel, Switzerland
| | - Hilary Stuart-Williams
- Research School of Biology and ARC Centre of Excellence for Translational Photosynthesis, Australian National University, Acton, Australian Capital Territory, Australia
| | - Graham D Farquhar
- Research School of Biology and ARC Centre of Excellence for Translational Photosynthesis, Australian National University, Acton, Australian Capital Territory, Australia
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11
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Ubierna N, Cernusak LA, Holloway-Phillips M, Busch FA, Cousins AB, Farquhar GD. Critical review: incorporating the arrangement of mitochondria and chloroplasts into models of photosynthesis and carbon isotope discrimination. PHOTOSYNTHESIS RESEARCH 2019; 141:5-31. [PMID: 30955143 DOI: 10.1007/s11120-019-00635-8] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/17/2018] [Accepted: 03/07/2019] [Indexed: 06/09/2023]
Abstract
The arrangement of mitochondria and chloroplasts, together with the relative resistances of cell wall and chloroplast, determine the path of diffusion out of the leaf for (photo)respired CO2. Traditional photosynthesis models have assumed a tight arrangement of chloroplasts packed together against the cell wall with mitochondria located behind the chloroplasts, deep inside the cytosol. Accordingly, all (photo)respired CO2 must cross the chloroplast before diffusing out of the leaf. Different arrangements have recently been considered, where all or part of the (photo)respired CO2 diffuses through the cytosol without ever entering the chloroplast. Assumptions about the path for the (photo)respiratory flux are particularly relevant for the calculation of mesophyll conductance (gm). If (photo)respired CO2 can diffuse elsewhere besides the chloroplast, apparent gm is no longer a mere physical resistance but a flux-weighted variable sensitive to the ratio of (photo)respiration to net CO2 assimilation. We discuss existing photosynthesis models in conjunction with their treatment of the (photo)respiratory flux and present new equations applicable to the generalized case where (photo)respired CO2 can diffuse both into the chloroplast and through the cytosol. Additionally, we present a new generalized Δ13C model that incorporates this dual diffusion pathway. We assess how assumptions about the fate of (photo)respired CO2 affect the interpretation of photosynthetic data and the challenges it poses for the application of different models.
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Affiliation(s)
- Nerea Ubierna
- Research School of Biology, Australian National University, Acton, ACT, 2601, Australia.
| | - Lucas A Cernusak
- College of Science and Engineering, James Cook University, Cairns, QLD, Australia
| | | | - Florian A Busch
- Research School of Biology, Australian National University, Acton, ACT, 2601, Australia
| | - Asaph B Cousins
- School of Biological Sciences, Molecular Plant Sciences, Washington State University, Pullman, WA, 99164-4236, USA
| | - Graham D Farquhar
- Research School of Biology, Australian National University, Acton, ACT, 2601, Australia
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12
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Giuliani R, Karki S, Covshoff S, Lin HC, Coe RA, Koteyeva NK, Quick WP, Von Caemmerer S, Furbank RT, Hibberd JM, Edwards GE, Cousins AB. Knockdown of glycine decarboxylase complex alters photorespiratory carbon isotope fractionation in Oryza sativa leaves. JOURNAL OF EXPERIMENTAL BOTANY 2019; 70:2773-2786. [PMID: 30840760 PMCID: PMC6506765 DOI: 10.1093/jxb/erz083] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/23/2018] [Accepted: 02/12/2019] [Indexed: 05/07/2023]
Abstract
The influence of reduced glycine decarboxylase complex (GDC) activity on leaf atmosphere CO2 and 13CO2 exchange was tested in transgenic Oryza sativa with the GDC H-subunit knocked down in leaf mesophyll cells. Leaf measurements on transgenic gdch knockdown and wild-type plants were carried out in the light under photorespiratory and low photorespiratory conditions (i.e. 18.4 kPa and 1.84 kPa atmospheric O2 partial pressure, respectively), and in the dark. Under approximately current ambient O2 partial pressure (18.4 kPa pO2), the gdch knockdown plants showed an expected photorespiratory-deficient phenotype, with lower leaf net CO2 assimilation rates (A) than the wild-type. Additionally, under these conditions, the gdch knockdown plants had greater leaf net discrimination against 13CO2 (Δo) than the wild-type. This difference in Δo was in part due to lower 13C photorespiratory fractionation (f) ascribed to alternative decarboxylation of photorespiratory intermediates. Furthermore, the leaf dark respiration rate (Rd) was enhanced and the 13CO2 composition of respired CO2 (δ13CRd) showed a tendency to be more depleted in the gdch knockdown plants. These changes in Rd and δ13CRd were due to the amount and carbon isotopic composition of substrates available for dark respiration. These results demonstrate that impairment of the photorespiratory pathway affects leaf 13CO2 exchange, particularly the 13C decarboxylation fractionation associated with photorespiration.
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Affiliation(s)
- Rita Giuliani
- School of Biological Sciences, Molecular Plant Sciences, Washington State University, Pullman, WA, USA
| | - Shanta Karki
- C4 Rice Center, International Rice Research Institute (IRRI), Los Baños, Philippines
| | - Sarah Covshoff
- Department of Plant Sciences, University of Cambridge, Cambridge, UK
| | - Hsiang-Chun Lin
- C4 Rice Center, International Rice Research Institute (IRRI), Los Baños, Philippines
| | - Robert A Coe
- C4 Rice Center, International Rice Research Institute (IRRI), Los Baños, Philippines
| | - Nuria K Koteyeva
- Laboratory of Anatomy and Morphology, V.L. Komarov Botanical Institute of the Russian Academy of Sciences, St. Petersburg, Russia
| | - W Paul Quick
- C4 Rice Center, International Rice Research Institute (IRRI), Los Baños, Philippines
- Department of Animal and Plant Sciences, University of Sheffield, Sheffield, UK
| | - Susanne Von Caemmerer
- Division of Plant Sciences, Research School of Biology, The Australian National University, Canberra, Australia
| | - Robert T Furbank
- Division of Plant Sciences, Research School of Biology, The Australian National University, Canberra, Australia
| | - Julian M Hibberd
- Department of Plant Sciences, University of Cambridge, Cambridge, UK
| | - Gerald E Edwards
- School of Biological Sciences, Molecular Plant Sciences, Washington State University, Pullman, WA, USA
| | - Asaph B Cousins
- School of Biological Sciences, Molecular Plant Sciences, Washington State University, Pullman, WA, USA
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13
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Flexas J, Cano FJ, Carriquí M, Coopman RE, Mizokami Y, Tholen D, Xiong D. CO2 Diffusion Inside Photosynthetic Organs. THE LEAF: A PLATFORM FOR PERFORMING PHOTOSYNTHESIS 2018. [DOI: 10.1007/978-3-319-93594-2_7] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
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14
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Ubierna N, Holloway-Phillips MM, Farquhar GD. Using Stable Carbon Isotopes to Study C 3 and C 4 Photosynthesis: Models and Calculations. Methods Mol Biol 2018; 1770:155-196. [PMID: 29978402 DOI: 10.1007/978-1-4939-7786-4_10] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/08/2023]
Abstract
Stable carbon isotopes are a powerful tool to study photosynthesis. Initial applications consisted of determining isotope ratios of plant biomass using mass spectrometry. Subsequently, theoretical models relating C-isotope values to gas exchange characteristics were introduced and tested against instantaneous online measurements of 13C photosynthetic discrimination. Beginning in the twenty-first century, tunable diode laser spectroscopes with sufficient precision for determining isotope mixing ratios became commercially available. This has allowed collection of large data sets, at low cost and with unprecedented temporal resolution. With more data and accompanying knowledge, it has become apparent that there is a need for increased complexity in models and calculations. This chapter describes instantaneous online measurements of 13C photosynthetic discrimination, provides recommendations for experimental setup, and presents a thorough compilation of equations needed for different applications.
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Affiliation(s)
- Nerea Ubierna
- School of Biological Sciences, Molecular Plant Sciences, Washington State University, Pullman, WA, USA.
| | | | - Graham D Farquhar
- Research School of Biology, Australian National University, Canberra, ACT, Australia
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15
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Crous KY, Wallin G, Atkin OK, Uddling J, Af Ekenstam A. Acclimation of light and dark respiration to experimental and seasonal warming are mediated by changes in leaf nitrogen in Eucalyptus globulus. TREE PHYSIOLOGY 2017; 37:1069-1083. [PMID: 28541536 DOI: 10.1093/treephys/tpx052] [Citation(s) in RCA: 28] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/26/2016] [Accepted: 05/10/2017] [Indexed: 06/07/2023]
Abstract
Quantifying the adjustments of leaf respiration in response to seasonal temperature variation and climate warming is crucial because carbon loss from vegetation is a large but uncertain part of the global carbon cycle. We grew fast-growing Eucalyptus globulus Labill. trees exposed to +3 °C warming and elevated CO2 in 10-m tall whole-tree chambers and measured the temperature responses of leaf mitochondrial respiration, both in light (RLight) and in darkness (RDark), over a 20-40 °C temperature range and during two different seasons. RLight was assessed using the Laisk method. Respiration rates measured at a standard temperature (25 °C - R25) were higher in warm-grown trees and in the warm season, related to higher total leaf nitrogen (N) investment with higher temperatures (both experimental and seasonal), indicating that leaf N concentrations modulated the respiratory capacity to changes in temperature. Once differences in leaf N were accounted for, there were no differences in R25 but the Q10 (i.e., short-term temperature sensitivity) was higher in late summer compared with early spring. The variation in RLight between experimental treatments and seasons was positively correlated with carboxylation capacity and photorespiration. RLight was less responsive to short-term changes in temperature than RDark, as shown by a lower Q10 in RLight compared with RDark. The overall light inhibition of R was ∼40%. Our results highlight the dynamic nature of leaf respiration to temperature variation and that the responses of RLight do not simply mirror those of RDark. Therefore, it is important not to assume that RLight is the same as RDark in ecosystem models, as doing so may lead to large errors in predicting plant CO2 release and productivity.
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Affiliation(s)
- K Y Crous
- Hawkesbury Institute for Environment, Western Sydney University, Hawkesbury Campus, Locked Bag 1797, Penrith, NSW 2751, Australia
| | - G Wallin
- Department of Biological and Environmental Sciences, University of Gothenburg, PO Box 461, SE-40530 Gothenburg, Sweden
| | - O K Atkin
- ARC Centre of Excellence in Plant Energy Biology, Division of Plant Sciences, Research School of Biology, Building 134, The Australian National University, Canberra, ACT 2601, Australia
| | - J Uddling
- Department of Biological and Environmental Sciences, University of Gothenburg, PO Box 461, SE-40530 Gothenburg, Sweden
| | - A Af Ekenstam
- Hawkesbury Institute for Environment, Western Sydney University, Hawkesbury Campus, Locked Bag 1797, Penrith, NSW 2751, Australia
- Department of Biological and Environmental Sciences, University of Gothenburg, PO Box 461, SE-40530 Gothenburg, Sweden
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16
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Barbour MM, Ryazanova S, Tcherkez G. Respiratory Effects on the Carbon Isotope Discrimination Near the Compensation Point. ADVANCES IN PHOTOSYNTHESIS AND RESPIRATION 2017. [DOI: 10.1007/978-3-319-68703-2_7] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
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17
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Lynch AH, Kruger NJ, Hedges REM, McCullagh JSO. Variability in the carbon isotope composition of individual amino acids in plant proteins from different sources: 1 Leaves. PHYTOCHEMISTRY 2016; 125:27-34. [PMID: 26948983 DOI: 10.1016/j.phytochem.2016.01.011] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/18/2015] [Revised: 01/14/2016] [Accepted: 01/19/2016] [Indexed: 06/05/2023]
Abstract
The natural carbon isotope composition of individual amino acids from plant leaf proteins has been measured to establish potential sources of variability. The plant leaves studied, taken from a range of plant groups (forbs, trees, grasses, and freshwater aquatic plants), showed no significant influence of either season or environment (water and light availability) on their Δδ(13)C values. Plant groups did, however, differ in carbon isotope composition, although no consistent differences were identified at the species level. A discriminant analysis model was constructed which allowed leaves from (1) nettles, (2) Pooideae, (3) other Poales, (4) trees and (5) freshwater higher plants to be distinguished from each other on the basis of their natural abundance (13)C/(12)C ratios of individual amino acids. Differences in carbon isotope composition are known to be retained, to some extent, in the tissues of their consumers, and hence an understanding of compound-specific variation in (13)C/(12)C fractional abundance in plants has the potential to provide dietary insights of value in archaeological and ecological studies.
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Affiliation(s)
- Anthony H Lynch
- Laboratory for Archaeology and the History of Art, South Parks Road, University of Oxford, Oxford OX1 3QY, UK; Department of Chemistry, Mansfield Road, University of Oxford, Oxford OX1 3TA, UK
| | - Nicholas J Kruger
- Department of Plant Sciences, South Parks Road, University of Oxford, Oxford OX1 3RB, UK
| | - Robert E M Hedges
- Laboratory for Archaeology and the History of Art, South Parks Road, University of Oxford, Oxford OX1 3QY, UK
| | - James S O McCullagh
- Department of Chemistry, Mansfield Road, University of Oxford, Oxford OX1 3TA, UK.
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18
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Ghashghaie J, Badeck FW, Girardin C, Huignard C, Aydinlis Z, Fonteny C, Priault P, Fresneau C, Lamothe-Sibold M, Streb P, Terwilliger VJ. Changes and their possible causes in δ13C of dark-respired CO2 and its putative bulk and soluble sources during maize ontogeny. JOURNAL OF EXPERIMENTAL BOTANY 2016; 67:2603-15. [PMID: 26970389 DOI: 10.1093/jxb/erw075] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/28/2023]
Abstract
The issues of whether, where, and to what extent carbon isotopic fractionations occur during respiration affect interpretations of plant functions that are important to many disciplines across the natural sciences. Studies of carbon isotopic fractionation during dark respiration in C3 plants have repeatedly shown respired CO2 to be (13)C enriched relative to its bulk leaf sources and (13)C depleted relative to its bulk root sources. Furthermore, two studies showed respired CO2 to become progressively (13)C enriched during leaf ontogeny and (13)C depleted during root ontogeny in C3 legumes. As such data on C4 plants are scarce and contradictory, we investigated apparent respiratory fractionations of carbon and their possible causes in different organs of maize plants during early ontogeny. As in the C3 plants, leaf-respired CO2 was (13)C enriched whereas root-respired CO2 was (13)C depleted relative to their putative sources. In contrast to the findings for C3 plants, however, not only root- but also leaf-respired CO2 became more (13)C depleted during ontogeny. Leaf-respired CO2 was highly (13)C enriched just after light-dark transition but the enrichment rapidly decreased over time in darkness. We conclude that (i) although carbon isotopic fractionations in C4 maize and leguminous C3 crop roots are similar, increasing phosphoenolpyruvate-carboxylase activity during maize ontogeny could have produced the contrast between the progressive (13)C depletion of maize leaf-respired CO2 and (13)C enrichment of C3 leaf-respired CO2 over time, and (ii) in both maize and C3 leaves, highly (13)C enriched leaf-respired CO2 at light-to-dark transition and its rapid decrease during darkness, together with the observed decrease in leaf malate content, may be the result of a transient effect of light-enhanced dark respiration.
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Affiliation(s)
- Jaleh Ghashghaie
- Ecologie Systématique Evolution, Université Paris-Sud, CNRS, AgroParisTech, Université Paris-Saclay, 91400 Orsay, France
| | - Franz W Badeck
- Genomics Research Centre, Council for Agricultural Research and Economics, 29017 Fiorenzuola d'Arda (PC), Italy
| | - Cyril Girardin
- UMR ECOSYS, INRA, AgroParisTech, Université Paris-Saclay, 78850 Thiverval-Grignon, France
| | - Christophe Huignard
- Ecologie Systématique Evolution, Université Paris-Sud, CNRS, AgroParisTech, Université Paris-Saclay, 91400 Orsay, France
| | - Zackarie Aydinlis
- Ecologie Systématique Evolution, Université Paris-Sud, CNRS, AgroParisTech, Université Paris-Saclay, 91400 Orsay, France
| | - Charlotte Fonteny
- Ecologie Systématique Evolution, Université Paris-Sud, CNRS, AgroParisTech, Université Paris-Saclay, 91400 Orsay, France
| | - Pierrick Priault
- Université de Lorraine, UMR Ecologie et Ecophysiologie Forestière, 54506 Vandoeuvre-lès-Nancy, France INRA, UMR Ecologie et Ecophysiologie Forestière, 54280 Champenoux, France
| | - Chantal Fresneau
- Ecologie Systématique Evolution, Université Paris-Sud, CNRS, AgroParisTech, Université Paris-Saclay, 91400 Orsay, France
| | - Marlène Lamothe-Sibold
- Institute of Plant Sciences Paris-Saclay, IPS2, CNRS, INRA, Université Paris-Sud, Université Evry, Université Paris-Saclay, 91405 Orsay, France
| | - Peter Streb
- Ecologie Systématique Evolution, Université Paris-Sud, CNRS, AgroParisTech, Université Paris-Saclay, 91400 Orsay, France
| | - Valery J Terwilliger
- Department of Geography, 1475 Jayhawk Drive, University of Kansas, Lawrence, KS 66045, USA School of Natural Sciences, 5200 North Lake Road, University of California, CA 95343, USA
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19
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Aranjuelo I, Erice G, Sanz-Sáez A, Abadie C, Gilard F, Gil-Quintana E, Avice JC, Staudinger C, Wienkoop S, Araus JL, Bourguignon J, Irigoyen JJ, Tcherkez G. Differential CO2 effect on primary carbon metabolism of flag leaves in durum wheat (Triticum durum Desf.). PLANT, CELL & ENVIRONMENT 2015; 38:2780-94. [PMID: 26081746 DOI: 10.1111/pce.12587] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/27/2014] [Accepted: 06/01/2015] [Indexed: 05/17/2023]
Abstract
C sink/source balance and N assimilation have been identified as target processes conditioning crop responsiveness to elevated CO2 . However, little is known about phenology-driven modifications of C and N primary metabolism at elevated CO2 in cereals such as wheat. Here, we examined the differential effect of elevated CO2 at two development stages (onset of flowering, onset of grain filling) in durum wheat (Triticum durum, var. Sula) using physiological measurements (photosynthesis, isotopes), metabolomics, proteomics and (15) N labelling. Our results show that growth at elevated CO2 was accompanied by photosynthetic acclimation through a lower internal (mesophyll) conductance but no significant effect on Rubisco content, maximal carboxylation or electron transfer. Growth at elevated CO2 altered photosynthate export and tended to accelerate leaf N remobilization, which was visible for several proteins and amino acids, as well as lysine degradation metabolism. However, grain biomass produced at elevated CO2 was larger and less N rich, suggesting that nitrogen use efficiency rather than photosynthesis is an important target for improvement, even in good CO2 -responsive cultivars.
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Affiliation(s)
- Iker Aranjuelo
- Plant Biology and Ecology Department, Science and Technology Faculty, University of the Basque Country, Leioa, 48940, Spain
| | - Gorka Erice
- Institute for Genomic Biology, University of Illinois, Urbana-Champaign, Urbana, IL, 61801, USA
| | - Alvaro Sanz-Sáez
- Department of Plant Biology and Crop Science, University of Illinois, Urbana-Champaign, Urbana, IL, 61801, USA
| | - Cyril Abadie
- Plateforme Métabolisme-Métabolome, Institut de Biologie des Plantes, Université Paris-Sud, Orsay, 91405, France
| | - Françoise Gilard
- Plateforme Métabolisme-Métabolome, Institut de Biologie des Plantes, Université Paris-Sud, Orsay, 91405, France
| | - Erena Gil-Quintana
- Dpto. Ciencias del Medio Natural, Universidad Pública de Navarra Campus de Arrosadía, Pamplona, 31006, Spain
| | - Jean-Christophe Avice
- Ecophysiologie Végétale, Agronomie et Nutritions NCS, INRA, UMR INRA/UCBN, Institut de Biologie Fondamentale et Appliquée, Université de Caen Basse-Normandie, Caen, 14032, France
| | - Christiana Staudinger
- Department of Ecogenomics and Systems Biology, University of Vienna, Vienna, 1090, Austria
| | - Stefanie Wienkoop
- Department of Ecogenomics and Systems Biology, University of Vienna, Vienna, 1090, Austria
| | - Jose L Araus
- Dpto de Biología Vegetal, Facultat de Biologia, Universidad de Barcelona, Barcelona, 08028, Spain
| | - Jacques Bourguignon
- Laboratoire Physiologie Cellulaire Végétale (PCV), CEA, iRTSV, Grenoble, 38054, France
- Réponse de la plante aux stress environnementaux et métaux lourds, Université Grenoble-Alpes, Grenoble, 38041, France
| | - Juan J Irigoyen
- Grupo de Fisiología del Estrés en Plantas (Dpto. de Biología Ambiental), Unidad Asociada al CSIC, EEAD, Zaragoza e ICVV, Logroño, Facultades de Ciencias yFarmacia, Universidad de Navarra, Pamplona, 31008, Spain
| | - Guillaume Tcherkez
- Research School of Biology, College of Medicine, Biology and Environment, Australian National University, Canberra, Australian Capital Territory, 2601, Australia
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20
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von Caemmerer S, Evans JR. Temperature responses of mesophyll conductance differ greatly between species. PLANT, CELL & ENVIRONMENT 2015; 38:629-37. [PMID: 25224884 DOI: 10.1111/pce.12449] [Citation(s) in RCA: 163] [Impact Index Per Article: 18.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/02/2014] [Revised: 08/19/2014] [Accepted: 08/20/2014] [Indexed: 05/04/2023]
Abstract
The temperature responses of mesophyll conductance (gm ) were investigated for nine species using carbon isotope techniques combining tunable diode laser spectroscopy and gas exchange measurements. Species included the evergreen trees Eucalyptus pauciflora and Quercus engelmannii; the tropical evergreen tree Lophostemon confertus; as well as the herbaceous species Nicotiana tabacum, Oryza sativa, Triticum aestivum, Gossypium hirsutum, Glycine max and Arabidopsis thaliana. Responses varied from a two- to threefold increase in mesophyll conductance between 15 and 40 °C observed for N. tabacum, G. hirsutum, G. max and E. pauciflora to almost no change in L. confertus and T. aestivum. To account for the different temperature responses between species, we suggest that there must be variation in both the activation energy for membrane permeability and the effective pathlength for liquid phase diffusion. Stomatal conductance was relatively independent of increases in leaf temperature and concomitant increases in leaf to air vapour pressure difference. Two exceptions were Eucalyptus and Gossypium, where stomatal conductance increased with temperature up to 35 °C despite increasing leaf to air vapour pressure. For a given species, temperature responses of stomatal and mesophyll conductance were independent of one another.
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Affiliation(s)
- Susanne von Caemmerer
- Division of Plant Sciences, Research School of Biology, The Australian National University, Canberra, Australian Capital Territory, 0200, Australia
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21
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Zhou Y, Stuart-Williams H, Grice K, Kayler ZE, Zavadlav S, Vogts A, Rommerskirchen F, Farquhar GD, Gessler A. Allocate carbon for a reason: priorities are reflected in the ¹³C/¹²C ratios of plant lipids synthesized via three independent biosynthetic pathways. PHYTOCHEMISTRY 2015; 111:14-20. [PMID: 25576502 DOI: 10.1016/j.phytochem.2014.12.005] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/20/2014] [Revised: 11/27/2014] [Accepted: 12/03/2014] [Indexed: 06/04/2023]
Abstract
It has long been theorized that carbon allocation, in addition to the carbon source and to kinetic isotopic effects associated with a particular lipid biosynthetic pathway, plays an important role in shaping the carbon isotopic composition ((13)C/(12)C) of lipids (Park and Epstein, 1961). If the latter two factors are properly constrained, valuable information about carbon allocation during lipid biosynthesis can be obtained from carbon isotope measurements. Published work of Chikaraishi et al. (2004) showed that leaf lipids isotopic shifts from bulk leaf tissue Δδ(13)C(bk-lp) (defined as δ(13)C(bulkleaftissue)-δ(13)C(lipid)) are pathway dependent: the acetogenic (ACT) pathway synthesizing fatty lipids has the largest isotopic shift, the mevalonic acid (MVA) pathway synthesizing sterols the lowest and the phytol synthesizing 1-deoxy-D-xylulose 5-phosphate (DXP) pathway gives intermediate values. The differences in Δδ(13)C(bk-lp) between C3 and C4 plants Δδ(13)C(bk-lp,C4-C3) are also pathway-dependent: Δδ(13)C(ACT)(bk-lp,C4-C3) > Δδ(13)C(DXP(bk-lp,C4-C3) > Δδ(13)C(MVA)(bk-lp,C4-C3). These pathway-dependent differences have been interpreted as resulting from kinetic isotopic effect differences of key but unspecified biochemical reactions involved in lipids biosynthesis between C3 and C4 plants. After quantitatively considering isotopic shifts caused by (dark) respiration, export-of-carbon (to sink tissues) and photorespiration, we propose that the pathway-specific differences Δδ(13)C(bk-lp,C4-C3) can be successfully explained by C4-C3 carbon allocation (flux) differences with greatest flux into the ACT pathway and lowest into the MVA pathways (when flux is higher, isotopic shift relative to source is smaller). Highest carbon allocation to the ACT pathway appears to be tied to the most stringent role of water-loss-minimization by leaf waxes (composed mainly of fatty lipids) while the lowest carbon allocation to the MVA pathway can be largely explained by the fact that sterols act as regulatory hormones and membrane fluidity modulators in rather low concentrations.
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Affiliation(s)
- Youping Zhou
- Institute for Landscape Biogeochemistry, ZALF, Germany; Department of Chemistry, Curtin University, Perth, Australia; SKLLQG, Chinese Academy of Sciences, Xi'an, China; Leibniz Institute for Freshwater Ecology & Inland Fisheries, Germany.
| | | | - Kliti Grice
- Department of Chemistry, Curtin University, Perth, Australia
| | | | | | - Angela Vogts
- Leibniz-Institut für Ostseeforschung, Rostock, Germany
| | | | | | - Arthur Gessler
- Institute for Landscape Biogeochemistry, ZALF, Germany; Swiss Federal Institute WSL, Birmensdorf, Switzerland
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22
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Gentsch L, Hammerle A, Sturm P, Ogée J, Wingate L, Siegwolf R, Plüss P, Baur T, Buchmann N, Knohl A. Carbon isotope discrimination during branch photosynthesis of Fagus sylvatica: a Bayesian modelling approach. PLANT, CELL & ENVIRONMENT 2014; 37:1516-1535. [PMID: 24372560 DOI: 10.1111/pce.12262] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/03/2013] [Revised: 11/05/2013] [Accepted: 12/04/2013] [Indexed: 06/03/2023]
Abstract
Field measurements of photosynthetic carbon isotope discrimination ((13)Δ) of Fagus sylvatica, conducted with branch bags and laser spectrometry, revealed a high variability of (13)Δ, both on diurnal and day-to-day timescales. We tested the prediction capability of three versions of a commonly used model for (13)Δ [called here comprehensive ((13)(Δcomp)), simplified ((13) Δsimple) and revised ((13)(Δrevised)) versions]. A Bayesian approach was used to calibrate major model parameters. Constrained estimates were found for the fractionation during CO(2) fixation in (13)(Δcomp), but not in (13)(Δsimple), and partially for the mesophyll conductance for CO(2)(gi). No constrained estimates were found for fractionations during mitochondrial and photorespiration, and for a diurnally variable apparent fractionation between current assimilates and mitochondrial respiration, specific to (13)(Δrevised). A quantification of parameter estimation uncertainties and interdependencies further helped explore model structure and behaviour. We found that (13)(Δcomp) usually outperformed (13)(Δsimple) because of the explicit consideration of gi and the photorespiratory fractionation in (13)(Δcomp) that enabled a better description of the large observed diurnal variation (≈9‰) of (13)Δ. Flux-weighted daily means of (13)Δ were also better predicted with (13)(Δcomp) than with (13)(Δsimple).
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Affiliation(s)
- Lydia Gentsch
- Institute of Agricultural Sciences, ETH Zurich, Universitätsstrasse 2, Zurich, 8092, Switzerland; UR1263 Ephyse, INRA, Villenave d'Ornon, 33140, France
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23
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Cernusak LA, Ubierna N, Winter K, Holtum JAM, Marshall JD, Farquhar GD. Environmental and physiological determinants of carbon isotope discrimination in terrestrial plants. THE NEW PHYTOLOGIST 2013; 200:950-65. [PMID: 23902460 DOI: 10.1111/nph.12423] [Citation(s) in RCA: 232] [Impact Index Per Article: 21.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/31/2013] [Accepted: 06/25/2013] [Indexed: 05/05/2023]
Abstract
Stable carbon isotope ratios (δ(13) C) of terrestrial plants are employed across a diverse range of applications in environmental and plant sciences; however, the kind of information that is desired from the δ(13) C signal often differs. At the extremes, it ranges between purely environmental and purely biological. Here, we review environmental drivers of variation in carbon isotope discrimination (Δ) in terrestrial plants, and the biological processes that can either damp or amplify the response. For C3 plants, where Δ is primarily controlled by the ratio of intercellular to ambient CO2 concentrations (ci /ca ), coordination between stomatal conductance and photosynthesis and leaf area adjustment tends to constrain the potential environmentally driven range of Δ. For C4 plants, variation in bundle-sheath leakiness to CO2 can either damp or amplify the effects of ci /ca on Δ. For plants with crassulacean acid metabolism (CAM), Δ varies over a relatively large range as a function of the proportion of daytime to night-time CO2 fixation. This range can be substantially broadened by environmental effects on Δ when carbon uptake takes place primarily during the day. The effective use of Δ across its full range of applications will require a holistic view of the interplay between environmental control and physiological modulation of the environmental signal.
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Affiliation(s)
- Lucas A Cernusak
- Department of Marine and Tropical Biology, James Cook University, Cairns, Qld, Australia
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24
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Evans JR, von Caemmerer S. Temperature response of carbon isotope discrimination and mesophyll conductance in tobacco. PLANT, CELL & ENVIRONMENT 2013; 36:745-56. [PMID: 22882584 DOI: 10.1111/j.1365-3040.2012.02591.x] [Citation(s) in RCA: 152] [Impact Index Per Article: 13.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/04/2023]
Abstract
The partial pressure of CO2 at the sites of carboxylation within chloroplasts depends on the conductance to CO2 diffusion from intercellular airspace to the sites of carboxylation, termed mesophyll conductance (gm ). We investigated the temperature response of gm in tobacco (Nicotiana tabacum) by combining gas exchange in high light, ambient CO2 in either 2 or 21% O2 with carbon isotope measurements using tuneable diode laser spectroscopy. The gm increased linearly with temperature in 2 or 21% O2 . In 21% O2 , isotope discrimination associated with gm decreased from 5.0 ± 0.2 to 1.8 ± 0.2‰ as temperature increased from 15 to 40 °C, but the photorespiratory contribution to the isotopic signal is significant. While the fractionation factor for photorespiration (f = 16.2 ± 0.7‰) was independent of temperature between 20 and 35 °C, discrimination associated with photorespiration increased from 1.1 ± 0.01 to 2.7 ± 0.02‰ from 15 to 40 °C. Other mitochondrial respiration contributed around 0.2 ± 0.03‰. The drawdown in CO2 partial pressure from ambient air to intercellular airspaces was nearly independent of leaf temperature. By contrast, the increase in gm with increasing leaf temperature resulted in the drawdown in CO2 partial pressure between intercellular airspaces and the sites of carboxylation decreasing substantially at high temperature.
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Affiliation(s)
- John R Evans
- Plant Science Division, Research School of Biology, The Australian National University, Canberra, Australian Capital Territory 0200, Australia.
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Tcherkez G, Mahé A, Guérard F, Boex-Fontvieille ERA, Gout E, Lamothe M, Barbour MM, Bligny R. Short-term effects of CO(2) and O(2) on citrate metabolism in illuminated leaves. PLANT, CELL & ENVIRONMENT 2012; 35:2208-2220. [PMID: 22646810 DOI: 10.1111/j.1365-3040.2012.02550.x] [Citation(s) in RCA: 25] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/01/2023]
Abstract
Although there is now a considerable literature on the inhibition of leaf respiration (CO(2) evolution) by light, little is known about the effect of other environmental conditions on day respiratory metabolism. In particular, CO(2) and O(2) mole fractions are assumed to cause changes in the tricarboxylic acid pathway (TCAP) but the amplitude and even the direction of such changes are still a matter of debate. Here, we took advantage of isotopic techniques, new simple equations and instant freeze sampling to follow respiratory metabolism in illuminated cocklebur leaves (Xanthium strumarium L.) under different CO(2) /O(2) conditions. Gas exchange coupled to online isotopic analysis showed that CO(2) evolved by leaves in the light came from 'old' carbon skeletons and there was a slight decrease in (13) C natural abundance when [CO(2) ] increased. This suggested the involvement of enzymatic steps fractionating more strongly against (13) C and thus increasingly limiting for the metabolic respiratory flux as [CO(2) ] increased. Isotopic labelling with (13) C(2) -2,4-citrate lead to (13) C-enriched Glu and 2-oxoglutarate (2OG), clearly demonstrating poor metabolism of citrate by the TCAP. There was a clear relationship between the ribulose-1,5-bisphosphate oxygenation-to-carboxylation ratio (v(o) /v(c) ) and the (13) C commitment to 2OG, demonstrating that 2OG and Glu synthesis via the TCAP is positively influenced by photorespiration.
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Affiliation(s)
- Guillaume Tcherkez
- Institut de Biologie des Plantes, CNRS UMR8618, Université Paris-Sud, 91405 Orsay Cedex, France.
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Merchant A, Buckley TN, Pfautsch S, Turnbull TL, Samsa GA, Adams MA. Site-specific responses to short-term environmental variation are reflected in leaf and phloem-sap carbon isotopic abundance of field grown Eucalyptus globulus. PHYSIOLOGIA PLANTARUM 2012; 146:448-59. [PMID: 22568657 DOI: 10.1111/j.1399-3054.2012.01638.x] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/13/2023]
Abstract
The carbon isotopic composition (δ(13) C) of plant material has been used extensively as an indirect measure of carbon fixation per volume of water used. More recently, the δ(13) C of phloem sap (δ(13) C(phl) ) has been used as a surrogate measure of short-term, canopy scale δ(13) C. Using a combination of δ(13) C physiological, structural and chemical indices from leaves and phloem sap of Eucalyptus globulus at sites of contrasting water availability, we sought to identify short-term, canopy scale resource limitations. Results illustrate that δ(13) C(phl) offers valid reflections of short-term, canopy scale values of leaf δ(13) C and tree water status. Under conditions limited by water, leaf and phloem sap photoassimilates differ in (13) C abundance of a magnitude large enough to significantly influence predictions of water use efficiency. This pattern was not detected among trees with adequate water supply indicating fractionation into heterotrophic tissues that may be sensitive to plant water status. Trees employed a range of physiological, biochemical and structural adaptations to acclimate to resource limitation that differed among sites providing a useful context upon which to interpret patterns in δ(13) C. Our results highlight that such easily characterized properties are ideal for use as minimally invasive tools to monitor growth and resilience of plants to variations in resource availability.
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Affiliation(s)
- Andrew Merchant
- Faculty of Agriculture, Food and Natural Resources, The University of Sydney, Sydney, Australia.
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Douthe C, Dreyer E, Brendel O, Warren CR. Is mesophyll conductance to CO 2 in leaves of three Eucalyptus species sensitive to short-term changes of irradiance under ambient as well as low O 2? FUNCTIONAL PLANT BIOLOGY : FPB 2012; 39:435-448. [PMID: 32480795 DOI: 10.1071/fp11190] [Citation(s) in RCA: 30] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/25/2011] [Accepted: 03/26/2012] [Indexed: 06/11/2023]
Abstract
Mesophyll conductance to CO2 (g m) limits the diffusion of CO2 to the sites of carboxylation, and may respond rapidly (within minutes) to abiotic factors. Using three Eucalyptus species, we tested the rapid response of g m to irradiance under 21% and 1% O2. We used simultaneous measurements of leaf gas exchange and discrimination against 13CO2 with a tuneable diode laser absorption spectrometer. Measurements under 1% O2 were used to limit uncertainties due to 13C-12C fractionation occurring during photorespiration. Switching irradiance from 600 to 200µmolm-2s-1 led to a ≈60% decrease of g m within minutes in all species under both 21% O2 and 1% O2. The g m response to irradiance is unlikely to be a computation artefact since using different values for the parameters of the discrimination model changed the absolute values of g m but did not affect the relative response to irradiance. Simulations showed that possible rapid changes of any parameter were unable to explain the observed variations of g m with irradiance, except for13C-12C fractionation during carboxylation (b), which, in turn, is dependent on the fraction of leaf C assimilated by phospho-enol pyruvate carboxylase (PEPc) (β). g m apparently increased by ≈30% when O2 was switched from 21% to 1% O2. Again, possible changes of β with O2 could explain this apparent g m response to O2. Nevertheless, large irradiance or O2-induced changes in β would be required to fully explain the observed changes in g m, reinforcing the hypothesis that g m is responsive to irradiance and possibly also to O2.
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Affiliation(s)
- Cyril Douthe
- INRA, Unité Mixte de Recherches 1147 'Ecologie et Ecophysiologie Forestières', F 54280 Champenoux, France
| | - Erwin Dreyer
- INRA, Unité Mixte de Recherches 1147 'Ecologie et Ecophysiologie Forestières', F 54280 Champenoux, France
| | - Oliver Brendel
- INRA, Unité Mixte de Recherches 1147 'Ecologie et Ecophysiologie Forestières', F 54280 Champenoux, France
| | - Charles R Warren
- University of Sydney, School of Biological Sciences, Heydon-Laurence Building, A08, The University of Sydney, NSW 2006, Australia
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Gilbert A, Silvestre V, Robins RJ, Remaud GS, Tcherkez G. Biochemical and physiological determinants of intramolecular isotope patterns in sucrose from C3, C4 and CAM plants accessed by isotopic 13C NMR spectrometry: a viewpoint. Nat Prod Rep 2012; 29:476-86. [DOI: 10.1039/c2np00089j] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
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Alexandrova AN, Jorgensen WL. On the mechanism and rate of spontaneous decomposition of amino acids. J Phys Chem B 2011; 115:13624-32. [PMID: 21995727 PMCID: PMC3241013 DOI: 10.1021/jp2081808] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Spontaneous decarboxylation of amino acids is among the slowest known reactions; it is much less facile than the cleavage of amide bonds in polypeptides. Establishment of the kinetics and mechanisms for this fundamental reaction is important for gauging the proficiency of enzymes. In the present study, multiple mechanisms for glycine decomposition in water are explored using QM/MM Monte Carlo simulations and free energy perturbation theory. Simple CO(2) detachment emerges as the preferred pathway for decarboxylation; it is followed by water-assisted proton transfer to yield the products: CO(2) and methylamine. The computed free energy of activation of 45 kcal/mol, and the resulting rate-constant of 1 × 10(-21) s(-1), can be compared with an extrapolated experimental rate constant of ~2 × 10(-17) s(-1) at 25 °C. The half-life for the reaction is more than 1 billion years. Furthermore, examination of deamination finds simple NH(3)-detachment yielding α-lactone to be the favored route, though it is less facile than decarboxylation by 6 kcal/mol. Ab initio and DFT calculations with the CPCM hydration model were also carried out for the reactions; the computed free energies of activation for glycine decarboxylation agree with the QM/MM result, whereas deamination is predicted to be more favorable. QM/MM calculations were also performed for decarboxylation of alanine; the computed barrier is 2 kcal/mol higher than for glycine in qualitative accord with experiment.
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Affiliation(s)
- Anastassia N Alexandrova
- Department of Chemistry and Biochemistry, University of California, Los Angeles, Los Angeles, California 90095-1569, USA.
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Douthe C, Dreyer E, Epron D, Warren CR. Mesophyll conductance to CO₂, assessed from online TDL-AS records of ¹³CO₂ discrimination, displays small but significant short-term responses to CO₂ and irradiance in Eucalyptus seedlings. JOURNAL OF EXPERIMENTAL BOTANY 2011; 62:5335-46. [PMID: 21841176 PMCID: PMC3223034 DOI: 10.1093/jxb/err141] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/15/2011] [Revised: 04/04/2011] [Accepted: 04/06/2011] [Indexed: 05/05/2023]
Abstract
Mesophyll conductance (g(m)) is now recognized as an important limiting process for photosynthesis, as it results in a significant decrease of CO(2) diffusion from substomatal cavities where water evaporation occurs, to chloroplast stroma. Over the past decade, an increasing number of studies proposed that g(m) can vary in the short term (e.g. minutes), but these variations are still controversial, especially those potentially induced by changing CO(2) and irradiance. In this study, g(m) data estimated with online (13)C discrimination recorded with a tunable diode laser absorption spectrometer (TDL-AS) during leaf gas exchange measurements, and based on the single point method, are presented. The data were obtained with three Eucalyptus species. A 50% decrease in g(m) was observed when the CO(2) mole fraction was increased from 300 μmol mol(-1) to 900 μmol mol(-1), and a 60% increase when irradiance was increased from 200 μmol mol(-1) to 1100 μmol mol(-1) photosynthetic photon flux density (PPFD). The relative contribution of respiration and photorespiration to overall (13)C discrimination was also estimated. Not taking this contribution into account may lead to a 50% underestimation of g(m) but had little effect on the CO(2)- and irradiance-induced changes. In conclusion, (i) the observed responses of g(m) to CO(2) and irradiance were not artefactual; (ii) the respiratory term is important to assess absolute values of g(m) but has no impact on the responses to CO(2) and PPFD; and (iii) increasing irradiance and reducing the CO(2) mole fraction results in rapid increases in g(m) in Eucalyptus seedlings.
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Affiliation(s)
- Cyril Douthe
- INRA, Unité Mixte de Recherches 1147 ‘Ecologie et Ecophysiologie Forestières’, F-54280 Champenoux, France
- Nancy Université, Unité Mixte de Recherches 1147 ‘Ecologie et Ecophysiologie Forestières’, Faculté des Sciences, F-54500 Vandoeuvre, France
- University of Sydney, School of Biological Sciences, Heydon-Laurence Building, A08, The University of Sydney, NSW 2006, Australia
| | - Erwin Dreyer
- INRA, Unité Mixte de Recherches 1147 ‘Ecologie et Ecophysiologie Forestières’, F-54280 Champenoux, France
- Nancy Université, Unité Mixte de Recherches 1147 ‘Ecologie et Ecophysiologie Forestières’, Faculté des Sciences, F-54500 Vandoeuvre, France
| | - Daniel Epron
- INRA, Unité Mixte de Recherches 1147 ‘Ecologie et Ecophysiologie Forestières’, F-54280 Champenoux, France
- Nancy Université, Unité Mixte de Recherches 1147 ‘Ecologie et Ecophysiologie Forestières’, Faculté des Sciences, F-54500 Vandoeuvre, France
| | - Charles R. Warren
- University of Sydney, School of Biological Sciences, Heydon-Laurence Building, A08, The University of Sydney, NSW 2006, Australia
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Tcherkez G, Mahé A, Hodges M. (12)C/(13)C fractionations in plant primary metabolism. TRENDS IN PLANT SCIENCE 2011; 16:499-506. [PMID: 21705262 DOI: 10.1016/j.tplants.2011.05.010] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/11/2011] [Revised: 05/18/2011] [Accepted: 05/25/2011] [Indexed: 05/13/2023]
Abstract
Natural (13)C abundance is now an unavoidable tool to study ecosystem and plant carbon economies. A growing number of studies take advantage of isotopic fractionation between carbon pools or (13)C abundance in respiratory CO(2) to examine the carbon source of respiration, plant biomass production or organic matter sequestration in soils. (12)C/(13)C isotope effects associated with plant metabolism are thus essential to understand natural isotopic signals. However, isotope effects of enzymes do not influence metabolites separately, but combine to yield a (12)C/(13)C isotopologue redistribution orchestrated by metabolic flux patterns. In this review, we summarise key metabolic isotope effects and integrate them into the corpus of plant primary carbon metabolism.
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Affiliation(s)
- Guillaume Tcherkez
- Institut de Biologie des Plantes, CNRS UMR 8618, Université Paris-Sud 11, 91405 Orsay cedex, France
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32
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Gilbert A, Silvestre V, Segebarth N, Tcherkez G, Guillou C, Robins RJ, Akoka S, Remaud GS. The intramolecular ¹³C-distribution in ethanol reveals the influence of the CO₂ -fixation pathway and environmental conditions on the site-specific ¹³C variation in glucose. PLANT, CELL & ENVIRONMENT 2011; 34:1104-1112. [PMID: 21410708 DOI: 10.1111/j.1365-3040.2011.02308.x] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/30/2023]
Abstract
Efforts to understand the cause of ¹²C versus ¹³C isotope fractionation in plants during photosynthesis and post-photosynthetic metabolism are frustrated by the lack of data on the intramolecular ¹³C-distribution in metabolites and its variation with environmental conditions. We have exploited isotopic carbon-13 nuclear magnetic resonance (¹³C NMR) spectrometry to measure the positional isotope composition (δ¹³C(i) , ‰) in ethanol samples from different origins: European wines, liquors and sugars from C₃, C₄ and crassulacean acid metabolism (CAM) plants. In C₃-ethanol samples, the methylene group was always ¹³C-enriched (∼2‰) relative to the methyl group. In wines, this pattern was correlated with both air temperature and δ(18)O of wine water, indicating that water vapour deficit may be a critical defining factor. Furthermore, in C₄-ethanol, the reverse relationship was observed (methylene-C relatively ¹³C-depleted), supporting the concept that photorespiration is the key metabolic process leading to the ¹³C distribution in C₃-ethanol. By contrast, in CAM-ethanol, the isotopic pattern was similar to but stronger than C₃-ethanol, with a relative ¹³C-enrichment in the methylene-C of up to 13‰. Plausible causes of this ¹³C-pattern are briefly discussed. As the intramolecular δ¹³C(i) -values in ethanol reflect that in source glucose, our data point out the crucial impact on the ratio of metabolic pathways sustaining glucose synthesis.
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Affiliation(s)
- Alexis Gilbert
- 1Interdisciplinary Chemistry: Synthesis,Analysis, Modelling (CEISAM), University of Nantes – CNRS UMR 6230, 2 rue de laHoussinière, BP 92208, F-44322 Nantes, France
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Tazoe Y, VON Caemmerer S, Estavillo GM, Evans JR. Using tunable diode laser spectroscopy to measure carbon isotope discrimination and mesophyll conductance to CO₂ diffusion dynamically at different CO₂ concentrations. PLANT, CELL & ENVIRONMENT 2011; 34:580-91. [PMID: 21251018 DOI: 10.1111/j.1365-3040.2010.02264.x] [Citation(s) in RCA: 113] [Impact Index Per Article: 8.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/05/2023]
Abstract
In C₃ leaves, the mesophyll conductance to CO₂ diffusion, g(m) , determines the drawdown in CO₂ concentration from intercellular airspace to the chloroplast stroma. Both g(m) and stomatal conductance limit photosynthetic rate and vary in response to the environment. We investigated the response of g(m) to changes in CO₂ in two Arabidopsis genotypes (including a mutant with open stomata, ost1), tobacco and wheat. We combined measurements of gas exchange with carbon isotope discrimination using tunable diode laser absorption spectroscopy with a CO₂ calibration system specially designed for a range of CO₂ and O₂ concentrations. CO₂ was initially increased from 200 to 1000 ppm and then decreased stepwise to 200 ppm and increased stepwise back to 1000 ppm, or the sequence was reversed. In 2% O₂ a step increase from 200 to 1000 ppm significantly decreased g(m) by 26-40% in all three species, whereas following a step decrease from 1000 to 200 ppm, the 26-38% increase in g(m) was not statistically significant. The response of g(m) to CO₂ was less in 21% O₂. Comparing wild type against the ost1 revealed that mesophyll and stomatal conductance varied independently in response to CO₂. We discuss the effects of isotope fractionation factors on estimating g(m) .
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Affiliation(s)
- Youshi Tazoe
- Graduate School of Biostudies, Kyoto University, Sakyo, Kyoto 606-8052, Japan
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34
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Tcherkez G, Mauve C, Lamothe M, Le Bras C, Grapin A. The 13C/12C isotopic signal of day-respired CO2 in variegated leaves of Pelargonium × hortorum. PLANT, CELL & ENVIRONMENT 2011; 34:270-283. [PMID: 20955224 DOI: 10.1111/j.1365-3040.2010.02241.x] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/30/2023]
Abstract
In leaves, although it is accepted that CO(2) evolved by dark respiration after illumination is naturally (13) C-enriched compared to organic matter or substrate sucrose, much uncertainty remains on whether day respiration produces (13) C-depleted or (13) C-enriched CO(2). Here, we applied equations described previously for mesocosm CO(2) exchange to investigate the carbon isotope composition of CO(2) respired by autotrophic and heterotrophic tissues of Pelargonium × hortorum leaves, taking advantage of leaf variegation. Day-respired CO(2) was slightly (13) C-depleted compared to organic matter both under 21% O(2) and 2% O(2). Furthermore, most, if not all CO(2) molecules evolved in the light came from carbon atoms that had been fixed previously before the experiments, in both variegated and green leaves. We conclude that the usual definition of day respiratory fractionation, that assumes carbon fixed by current net photosynthesis is the respiratory substrate, is not valid in Pelargonium leaves under our conditions. In variegated leaves, total organic matter was slightly (13) C-depleted in white areas and so were most primary metabolites. This small isotopic difference between white and green areas probably came from the small contribution of photosynthetic CO(2) refixation and the specific nitrogen metabolism in white leaf areas.
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Affiliation(s)
- Guillaume Tcherkez
- Plateforme Métabolisme-Métabolome IFR87, Institut de Biologie des Plantes, UMR CNRS 8618, Bâtiment 630, Université Paris-Sud 11, 91405 Orsay cedex, France.
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Bickford CP, Hanson DT, McDowell NG. Influence of diurnal variation in mesophyll conductance on modelled 13C discrimination: results from a field study. JOURNAL OF EXPERIMENTAL BOTANY 2010; 61:3223-33. [PMID: 20501745 PMCID: PMC2905191 DOI: 10.1093/jxb/erq137] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/16/2010] [Revised: 04/26/2010] [Accepted: 04/28/2010] [Indexed: 05/07/2023]
Abstract
Mesophyll conductance to CO(2) (g(m)) limits carbon assimilation and influences carbon isotope discrimination (Delta) under most environmental conditions. Current work is elucidating the environmental regulation of g(m), but the influence of g(m) on model predictions of Delta remains poorly understood. In this study, field measurements of Delta and g(m) were obtained using a tunable diode laser spectroscope coupled to portable photosynthesis systems. These data were used to test the importance of g(m) in predicting Delta using the comprehensive Farquhar model of Delta (Delta(comp)), where g(m) was parameterized using three methods based on: (i) mean g(m); (ii) the relationship between stomatal conductance (g(s)) and g(m); and (iii) the relationship between time of day (TOD) and g(m). Incorporating mean g(m), g(s)-based g(m), and TOD-based g(m) did not consistently improve Delta(comp) predictions of field-grown juniper compared with the simple model of Delta (Delta(simple)) that omits fractionation factors associated with g(m) and decarboxylation. Sensitivity tests suggest that b, the fractionation due to carboxylation, was lower (25 per thousand) than the value commonly used in Delta(comp) (29 per thousand) and Delta(simple) (27 per thousand). These results demonstrate the limits of all tested models in predicting observed juniper Delta, largely due to unexplained offsets between predicted and observed values that were not reconciled in sensitivity tests of variability in g(m), b, or e, the day respiratory fractionation.
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Affiliation(s)
- Christopher P Bickford
- University of New Mexico, Department of Biology, MSC03-2020, Albuquerque, NM 87131, USA.
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Graham LE, Cook ME, Hanson DT, Pigg KB, Graham JM. Rolled liverwort mats explain major Prototaxites features: Response to commentaries. AMERICAN JOURNAL OF BOTANY 2010; 97:1079-1086. [PMID: 21616860 DOI: 10.3732/ajb.1000172] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/30/2023]
Abstract
In volume 97(2) of the American Journal of Botany (pp. 268-275), we published an article entitled "Structural, physiological, and stable carbon isotopic evidence that the enigmatic Paleozoic fossil Prototaxites formed from rolled liverwort mats". Here, we respond to a letter and a commentary on our article in the present issue, welcoming this opportunity to continue the scientific dialogue about an issue that has long been stimulating and controversial. For the reader's benefit, we first briefly describe the recent scholarly context of our article.
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Affiliation(s)
- Linda E Graham
- Department of Botany, University of Wisconsin, Madison, Wisconsin 53706-1381 USA
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Tcherkez G, Schäufele R, Nogués S, Piel C, Boom A, Lanigan G, Barbaroux C, Mata C, Elhani S, Hemming D, Maguas C, Yakir D, Badeck FW, Griffiths H, Schnyder H, Ghashghaie J. On the 13C/12C isotopic signal of day and night respiration at the mesocosm level. PLANT, CELL & ENVIRONMENT 2010; 33:900-913. [PMID: 20082670 DOI: 10.1111/j.1365-3040.2010.02115.x] [Citation(s) in RCA: 38] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/28/2023]
Abstract
While there is currently intense effort to examine the (13)C signal of CO(2) evolved in the dark, less is known on the isotope composition of day-respired CO(2). This lack of knowledge stems from technical difficulties to measure the pure respiratory isotopic signal: day respiration is mixed up with photorespiration, and there is no obvious way to separate photosynthetic fractionation (pure c(i)/c(a) effect) from respiratory effect (production of CO(2) with a different delta(13)C value from that of net-fixed CO(2)) at the ecosystem level. Here, we took advantage of new simple equations, and applied them to sunflower canopies grown under low and high [CO(2)]. We show that whole mesocosm-respired CO(2) is slightly (13)C depleted in the light at the mesocosm level (by 0.2-0.8 per thousand), while it is slightly (13)C enriched in darkness (by 1.5-3.2 per thousand). The turnover of the respiratory carbon pool after labelling appears similar in the light and in the dark, and accordingly, a hierarchical clustering analysis shows a close correlation between the (13)C abundance in day- and night-evolved CO(2). We conclude that the carbon source for respiration is similar in the dark and in the light, but the metabolic pathways associated with CO(2) production may change, thereby explaining the different (12)C/(13)C respiratory fractionations in the light and in the dark.
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Affiliation(s)
- Guillaume Tcherkez
- Ecologie Systématique Evolution, Bâtiment 362, Université Paris-Sud 11, 91405 Orsay cedex, Paris, France.
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Tcherkez G. Natural 15N/ 14N isotope composition in C 3 leaves: are enzymatic isotope effects informative for predicting the 15N-abundance in key metabolites? FUNCTIONAL PLANT BIOLOGY : FPB 2010; 38:1-12. [PMID: 32480857 DOI: 10.1071/fp10091] [Citation(s) in RCA: 42] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/22/2010] [Accepted: 10/24/2010] [Indexed: 06/11/2023]
Abstract
Although nitrogen isotopes are viewed as important tools for understanding plant N acquisition and allocation, the current interpretation of natural 15N-abundances (δ15N values) is often impaired by substantial variability among individuals or between species. Such variability is likely to stem from the fact that 15N-abundance of assimilated N is not preserved during N metabolism and redistribution within the plant; that is, 14N/15N isotope effects associated with N metabolic reactions are certainly responsible for isotopic shifts between organic-N (amino acids) and absorbed inorganic N (nitrate). Therefore, to gain insights into the metabolic origin of 15N-abundance in plants, the present paper reviews enzymatic isotope effects and integrates them into a metabolic model at the leaf level. Using simple steady-state equations which satisfactorily predict the δ15N value of amino acids, it is shown that the sensitivity of δ15N values to both photorespiratory and N-input (reduction by nitrate reductase) rates is quite high. In other words, the variability in δ15N values observed in nature might originate from subtle changes in metabolic fluxes or environment-driven effects, such as stomatal closure that in turn changes v0, the Rubisco-catalysed oxygenation rate.
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Affiliation(s)
- Guillaume Tcherkez
- Institut de Biologie des Plantes, CNRS UMR 8618, Université Paris-Sud 11, 91405 Orsay Cedex, France. Email
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Ogée J, Barbour MM, Wingate L, Bert D, Bosc A, Stievenard M, Lambrot C, Pierre M, Bariac T, Loustau D, Dewar RC. A single-substrate model to interpret intra-annual stable isotope signals in tree-ring cellulose. PLANT, CELL & ENVIRONMENT 2009; 32:1071-1090. [PMID: 19422614 DOI: 10.1111/j.1365-3040.2009.01989.x] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/27/2023]
Abstract
The carbon and oxygen stable isotope composition of wood cellulose (delta(13)C(cellulose) and delta(18)O(cellulose), respectively) reveal well-defined seasonal variations that contain valuable records of past climate, leaf gas exchange and carbon allocation dynamics within the trees. Here, we present a single-substrate model for wood growth to interpret seasonal isotopic signals collected in an even-aged maritime pine plantation growing in South-west France, where climate, soil and flux variables were also monitored. Observed seasonal patterns in delta(13)C(cellulose) and delta(18)O(cellulose) were different between years and individuals, and mostly captured by the model, suggesting that the single-substrate hypothesis is a good approximation for tree ring studies on Pinus pinaster, at least for the environmental conditions covered by this study. A sensitivity analysis revealed that the model was mostly affected by five isotopic discrimination factors and two leaf gas-exchange parameters. Modelled early wood signals were also very sensitive to the date when cell wall thickening begins (t(wt)). Our model could therefore be used to reconstruct t(wt) time series and improve our understanding of how climate influences this key parameter of xylogenesis.
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Affiliation(s)
- J Ogée
- Ephyse, Inra, Bordeaux, BP81, 33883 Villenave d'Ornon, France.
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Bickford CP, McDowell NG, Erhardt EB, Hanson DT. High-frequency field measurements of diurnal carbon isotope discrimination and internal conductance in a semi-arid species, Juniperus monosperma. PLANT, CELL & ENVIRONMENT 2009; 32:796-810. [PMID: 19220783 DOI: 10.1111/j.1365-3040.2009.01959.x] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/27/2023]
Abstract
We present field observations of carbon isotope discrimination (Delta) and internal conductance of CO(2) (g(i)) collected using tunable diode laser spectroscopy (TDL). Delta ranged from 12.0 to 27.4 per thousand over diurnal periods with daily means from 16.3 +/- 0.2 per thousand during drought to 19.0 +/- 0.5 per thousand during monsoon conditions. We observed a large range in g(i), with most estimates between 0.04 and 4.0 micromol m(-2) s(-1) Pa(-1). We tested the comprehensive Farquhar, O'Leary and Berry model of Delta (Delta(comp)), a simplified form of Delta(comp) (Delta(simple)) and a recently suggested amendment (Delta(revised)). Sensitivity analyses demonstrated that varying g(i) had a substantial effect on Delta(comp), resulting in mean differences between observed Delta (Delta(obs)) and Delta(comp) ranging from 0.04 to 9.6 per thousand. First-order regressions adequately described the relationship between Delta and the ratio of substomatal to atmospheric CO(2) partial pressure (p(i)/p(a)) on all 3 d, but second-order models better described the relationship in July and August. The three tested models each best predicted Delta(obs) on different days. In June, Delta(simple) outperformed Delta(comp) and Delta(revised), but incorporating g(i) and all non-photosynthetic fractionations improved model predictions in July and August.
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Lanigan GJ, Betson N, Griffiths H, Seibt U. Carbon isotope fractionation during photorespiration and carboxylation in Senecio. PLANT PHYSIOLOGY 2008; 148:2013-20. [PMID: 18923019 PMCID: PMC2593675 DOI: 10.1104/pp.108.130153] [Citation(s) in RCA: 34] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/20/2008] [Accepted: 10/12/2008] [Indexed: 05/18/2023]
Abstract
The magnitude of fractionation during photorespiration and the effect on net photosynthetic (13)C discrimination (Delta) were investigated for three Senecio species, S. squalidus, S. cineraria, and S. greyii. We determined the contributions of different processes during photosynthesis to Delta by comparing observations (Delta(obs)) with discrimination predicted from gas-exchange measurements (Delta(pred)). Photorespiration rates were manipulated by altering the O(2) partial pressure (pO(2)) in the air surrounding the leaves. Contributions from (13)C-depleted photorespiratory CO(2) were largest at high pO(2). The parameters for photorespiratory fractionation (f), net fractionation during carboxylation by Rubisco and phosphoenolpyruvate carboxylase (b), and mesophyll conductance (g(i)) were determined simultaneously for all measurements. Instead of using Delta(obs) data to obtain g(i) and f successively, which requires that b is known, we treated b, f, and g(i) as unknowns. We propose this as an alternative approach to analyze measurements under field conditions when b and g(i) are not known or cannot be determined in separate experiments. Good agreement between modeled and observed Delta was achieved with f = 11.6 per thousand +/- 1.5 per thousand, b = 26.0 per thousand +/- 0.3 per thousand, and g(i) of 0.27 +/- 0.01, 0.25 +/- 0.01, and 0.22 +/- 0.01 mol m(-2) s(-1) for S. squalidus, S. cineraria, and S. greyii, respectively. We estimate that photorespiratory fractionation decreases Delta by about 1.2 per thousand on average under field conditions. In addition, diurnal changes in Delta are likely to reflect variations in photorespiration even at the canopy level. Our results emphasize that the effects of photorespiration must be taken into account when partitioning net CO(2) exchange of ecosystems into gross fluxes of photosynthesis and respiration.
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Affiliation(s)
- Gary J Lanigan
- Physiological Ecology Group, Department of Plant Sciences, University of Cambridge, Cambridge CB2 3EA, United Kingdom
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Gessler A, Tcherkez G, Peuke AD, Ghashghaie J, Farquhar GD. Experimental evidence for diel variations of the carbon isotope composition in leaf, stem and phloem sap organic matter in Ricinus communis. PLANT, CELL & ENVIRONMENT 2008; 31:941-953. [PMID: 18331588 DOI: 10.1111/j.1365-3040.2008.01806.x] [Citation(s) in RCA: 40] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/26/2023]
Abstract
Carbon isotope fractionation in metabolic processes following carboxylation of ribulose-1,5-bisphosphate (RuBP) is not as well described as the discrimination during photosynthetic CO(2) fixation. However, post-carboxylation fractionation can influence the diel variation of delta(13)C of leaf-exported organic matter and can cause inter-organ differences in delta(13)C. To obtain a more mechanistic understanding of post-carboxylation modification of the isotopic signal as governed by physiological and environmental controls, we combined the modelling approach of Tcherkez et al., which describes the isotopic fractionation in primary metabolism with the experimental determination of delta(13)C in leaf and phloem sap and root carbon pools during a full diel course. There was a strong diel variation of leaf water-soluble organic matter and phloem sap sugars with relatively (13)C depleted carbon produced and exported during the day and enriched carbon during the night. The isotopic modelling approach reproduces the experimentally determined day-night differences in delta(13)C of leaf-exported carbon in Ricinus communis. These findings support the idea that patterns of transitory starch accumulation and remobilization govern the diel rhythm of delta(13)C in organic matter exported by leaves. Integrated over the whole 24 h day, leaf-exported carbon was enriched in (13)C as compared with the primary assimilates. This may contribute to the well-known--yet poorly explained--relative (13)C depletion of autotrophic organs compared with other plant parts. We thus emphasize the need to consider post-carboxylation fractionations for studies that use delta(13)C for assessing environmental effects like water availability on ratio of mole fractions of CO(2) inside and outside the leaf (e.g. tree ring studies), or for partitioning of CO(2) fluxes at the ecosystem level.
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Affiliation(s)
- Arthur Gessler
- Environmental Biology Group, Research School of Biological Sciences, Australian National University, GPO Box 475, Canberra, ACT 2601, Australia.
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Tcherkez G, Farquhar GD. On the effect of heavy water (D 2O) on carbon isotope fractionation in photosynthesis. FUNCTIONAL PLANT BIOLOGY : FPB 2008; 35:201-212. [PMID: 32688774 DOI: 10.1071/fp07282] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/28/2007] [Accepted: 02/18/2008] [Indexed: 06/11/2023]
Abstract
Internal conductance to carbon dioxide is a key aspect of leaf photosynthesis although is still not well understood. It is thought that it comprises two components, namely, a gas phase component (diffusion from intercellular spaces to cell walls) and a liquid phase component (dissolution, diffusion in water, hydration equilibrium). Here we use heavy water (D2O), which is known to slow down CO2 hydration by a factor of nearly three. Using 12C/13C stable isotope techniques and Xanthium strumarium L. leaves, we show that the on-line carbon isotope discrimination (Δ13C, or Δobs) associated with photosynthesis is not significantly decreased by heavy water, and that the internal conductance, estimated with relationships involving the deviation of Δ13C, decreased by 8-40% in 21% O2. It is concluded that in typical conditions, the CO2-hydration equilibrium does not exert an effect on CO2 assimilation larger than 9%. The carbon isotope discrimination associated with CO2 addition to ribulose-1,5,bisphosphate by Rubisco is slightly decreased by heavy water. This effect is proposed to originate from the use of solvent-derived proton/deuteron during the last step of the catalytic cycle of the enzyme (hydration/cleavage).
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Affiliation(s)
- Guillaume Tcherkez
- Plateforme Métabolisme-Métabolome, IFR87, Université Paris-Sud XI, 91405 Orsay, France
| | - Graham D Farquhar
- Environmental Biology Group, Research School of Biological Sciences, Australian National University, Canberra, ACT 2601, Australia
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Tcherkez G, Farquhar GD. On the 16O/ 18O isotope effect associated with photosynthetic O 2 production. FUNCTIONAL PLANT BIOLOGY : FPB 2007; 34:1049-1052. [PMID: 32689433 DOI: 10.1071/fp07168] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/02/2007] [Accepted: 09/13/2007] [Indexed: 06/11/2023]
Abstract
While photosynthetically evolved O2 has been repeatedly shown to have nearly the same oxygen isotope composition as source water so that there is no corresponding 16O/18O isotope effect, some recent 18O-enrichment studies suggest that a large isotope effect may occur, thus feeding a debate in the literature. Here, the classical theory of isotope effects was applied to show that a very small isotope effect is indeed expected during O2 production. Explanations of the conflicting results are briefly discussed.
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Affiliation(s)
- Guillaume Tcherkez
- Plateforme Métabolisme-Métabolome, IFR87, Université Paris-Sud XI, Orsay 91405, France
| | - Graham D Farquhar
- Environmental Biology Group, Research School of Biological Sciences, Australian National University, Canberra, ACT 2601, Australia
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