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Updated: Aug 12, 2026
11:09
Relating Stomatal Conductance to Leaf Functional Traits
Published on: October 12, 2015
Internal conductance to CO(2) diffusion and C(18)OO discrimination in C(3) leaves
1Department of Environmental Science and Energy Research, Weizmann Institute of Science, 76100 Rehovot, Israel.
Plant Physiology
|May 12, 2000
Summary
Photosynthesis involves oxygen exchange in chloroplasts, affecting carbon dioxide (CO2) discrimination. This study quantizes CO2 conductance within plant cells, revealing carbonic anhydrase activity influences CO2 assimilation, particularly in plants with low internal conductances.
Area of Science:
- Plant Physiology
- Biochemistry
- Isotope Geochemistry
Background:
- Oxygen isotope discrimination during photosynthesis is influenced by oxygen exchange between CO2 and water within chloroplasts.
- This exchange is catalyzed by carbonic anhydrase (CA), impacting the discrimination against C18OO (Delta(18)O).
Purpose of the Study:
- To derive CO2 concentration at the chloroplast surface (c(cs)) using measured Delta(18)O.
- To partition internal CO2 conductance (g(i)) into cell wall (g(w)) and chloroplast (g(ch)) components.
- To investigate the relationship between CA activity and chloroplast CO2 conductance.
Main Methods:
- Constraining chloroplast water delta(18)O (delta(e)) using transpired water analysis.
- Measuring CO2-H2O isotopic equilibrium (theta(eq)) via CA activity assays.
- Utilizing a leaf cuvette mass spectrometer system to measure Delta(18)O and gas exchange parameters (c(i), c(c)).
Main Results:
- Chloroplast CO2 concentration (c(cs)) was determined from Delta(18)O measurements.
- Internal CO2 conductance (g(i)) was partitioned into g(w) and g(ch) using gas exchange and isotopic data.
- Chloroplast conductance (g(ch)) was found to be variable (0.42-1.13 mol m(-2) s(-1)) and directly proportional to CA activity.
Conclusions:
- Carbonic anhydrase activity significantly influences chloroplast CO2 conductance.
- The impact of CA on CO2 assimilation is most pronounced in plants exhibiting low internal conductances.
- This study provides a novel method for quantifying CO2 conductance within plant cells using stable isotope techniques.
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