Journal
PLANT CELL AND ENVIRONMENT
Volume 35, Issue 12, Pages 2087-2103Publisher
WILEY
DOI: 10.1111/j.1365-3040.2012.02538.x
Keywords
CO2; compensation point; internal conductance; PEPC; photorespiration; refixation; temperature
Categories
Funding
- Chinese Academy of Sciences [2009Y2AS10]
- National Science Foundation of China [31050110127, 30970213]
- Ministry of Science and Technology of China [2011DFA31070]
- Fonds de Recherche sur la Nature et les Technologies du Quebec
- Canada Foundation for Innovation
- Natural Sciences and Engineering Research Council of Canada Discovery Grant
- French Agence Nationale de la Recherche (LEAFFLUX project) [BLAN 07-1-192876]
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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 (g(m)), significantly constrains the rate of photosynthesis. Here we show that estimates of g(m) 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 g(m) 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 g(m). We further show that the amount of photo(respiratory) CO2 that is refixed by Rubisco can be directly estimated through measurements of g(m).
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