Variable mesophyll conductance revisited: theoretical background and experimental implications

Authors

  • DANNY THOLEN,

    Corresponding author
    1. State Key Laboratory of Hybrid Rice Research, Chinese Academy of Sciences (CAS) and Max Planck Society (MPG) Partner Institute for Computational Biology, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences, Yueyang Road 320, Shanghai, 200031, China
    2. CAS Key Laboratory of Computational Biology, CAS-MPG Partner Institute for Computational Biology, Shanghai Institute for Biological Sciences, Chinese Academy of Sciences, Yueyang Road 320, Shanghai, 200031, China
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    • These two authors contributed equally to this work.

  • GILBERT ETHIER,

    1. Université Laval, Centre de Recherche en Horticulture, Pavillon de l'Envirotron, Québec, Canada
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    • These two authors contributed equally to this work.

  • BERNARD GENTY,

    1. Commissariat à l'Energie Atomique et aux Energies Alternatives, Direction des Sciences du Vivant, Institut de Biologie Environnementale et de Biotechnologie, Laboratoire d'Ecophysiologie Moléculaire des Plantes, CEA Cadarache, 13108 Saint-Paul-lez-Durance, France
    2. Centre National de la Recherche Scientifique, UMR 6191 Biologie Végétale et Microbiologie Environnementale, 13108 Saint-Paul-lez-Durance, France
    3. Aix Marseille Université, UMR 6191 Biologie Végétale et Microbiologie Environnementale, 13108 Saint-Paul-lez-Durance, France
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  • STEEVE PEPIN,

    1. Université Laval, Centre de Recherche en Horticulture, Pavillon de l'Envirotron, Québec, Canada
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  • XIN-GUANG ZHU

    1. State Key Laboratory of Hybrid Rice Research, Chinese Academy of Sciences (CAS) and Max Planck Society (MPG) Partner Institute for Computational Biology, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences, Yueyang Road 320, Shanghai, 200031, China
    2. CAS Key Laboratory of Computational Biology, CAS-MPG Partner Institute for Computational Biology, Shanghai Institute for Biological Sciences, Chinese Academy of Sciences, Yueyang Road 320, Shanghai, 200031, China
    3. Institute of Plant Physiology and Ecology, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences, Shanghai, China
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D. Tholen. E-mail: thalecress+p@gmail.com

ABSTRACT

The CO2 concentration at the site of carboxylation inside the chloroplast stroma depends not only on the stomatal conductance, but also on the conductance of CO2 between substomatal cavities and the site of CO2 fixation. This conductance, commonly termed mesophyll conductance (gm), significantly constrains the rate of photosynthesis. Here we show that estimates of gm are influenced by the amount of respiratory and photorespiratory CO2 from the mitochondria diffusing towards the chloroplasts. This results in an apparent CO2 and oxygen sensitivity of gm that does not imply a change in intrinsic diffusion properties of the mesophyll, but depends on the ratio of mitochondrial CO2 release to chloroplast CO2 uptake. We show that this effect (1) can bias the estimation of the CO2 photocompensation point and non-photorespiratory respiration in the light; (2) can affect the estimates of ribulose 1·5-bisphosphate carboxylase/oxygenase (Rubisco) kinetic constants in vivo; and (3) results in an apparent obligatory correlation between stomatal conductance and gm. We further show that the amount of photo(respiratory) CO2 that is refixed by Rubisco can be directly estimated through measurements of gm.

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