Variable mesophyll conductance revisited: theoretical background and experimental implications

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 con...

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Bibliographic Details
Published in:Plant, cell and environment cell and environment, 2012-12, Vol.35 (12), p.2087-2103
Main Authors: THOLEN, DANNY, ETHIER, GILBERT, GENTY, BERNARD, PEPIN, STEEVE, ZHU, XIN‐GUANG
Format: Article
Language:English
Subjects:
Biological and medical sciences
carbon dioxide
Carbon Dioxide - metabolism
carboxylation
chloroplasts
Chloroplasts - metabolism
CO2
compensation point
Fundamental and applied biological sciences. Psychology
internal conductance
mesophyll
Mesophyll Cells - physiology
mitochondria
Mitochondria - metabolism
oxygen
PEPC
photorespiration
Photosynthesis
refixation
ribulose-bisphosphate carboxylase
stomatal conductance
Temperature
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Summary: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.
ISSN:0140-7791
1365-3040
DOI:10.1111/j.1365-3040.2012.02538.x