Light and CO2 do not affect the mesophyll conductance to CO2 diffusion in wheat leaves
Youshi Tazoe1, Susanne von Caemmerer, Murray R Badger
1The Australian National University, Canberra, Australia.
Journal of Experimental Botany
|March 4, 2009
Summary
Mesophyll conductance (g(m)) in wheat is unaffected by light intensity or CO(2) levels. This study investigated how photon flux density (PFD) and partial pressure of CO(2) (pCO(2)) influence CO(2) diffusion within leaves.
Area of Science:
- Plant Physiology
- Photosynthesis Research
- Biophysical Plant Science
Background:
- CO(2) diffusion into C(3) plant leaves is limited by stomata, intercellular airspaces, and liquid phase into chloroplasts.
- While stomatal conductance (g(s)) is well-studied, the response of mesophyll conductance (g(m)) to environmental factors like light and CO(2) is less understood.
Purpose of the Study:
- To investigate the impact of photon flux density (PFD) and partial pressure of CO(2) (pCO(2)) on mesophyll conductance (g(m)) in wheat leaves.
- To determine if g(m) varies with changes in light intensity or intercellular CO(2) concentration.
Main Methods:
- Combined gas exchange measurements with carbon isotope discrimination analysis.
- Utilized a membrane inlet mass spectrometer for precise measurements.
- Conducted experiments under low O(2) (2%) to minimize photorespiration effects.
- Estimated g(m) using carbon isotope discrimination (Delta), CO(2) concentrations, assimilation, and respiration rates.
Main Results:
- Mesophyll conductance (g(m)) in wheat was found to be independent of PFD across a range of 200–1500 µmol m⁻² s⁻¹.
- g(m) also showed independence from intercellular partial pressure of CO(2) (p(i)) between 80 and 500 microbar.
- Respiration contributed significantly and variably to observed discrimination, influenced by CO(2) source differences.
Conclusions:
- Mesophyll conductance (g(m)) in wheat is not significantly affected by physiological levels of photon flux density (PFD) or intercellular CO(2) partial pressure (p(i)).
- These findings suggest that under the tested conditions, internal CO(2) diffusion limitations within the leaf mesophyll do not change with light or CO(2) availability.
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