Details

Autor(en) / Beteiligte

• Carl J. Bernacchi
• Archie R. Portis
• Nakano, Hiromi
• von Caemmerer, Susanne
• Long, Stephen P.

Titel

Temperature Response of Mesophyll Conductance. Implications for the Determination of Rubisco Enzyme Kinetics and for Limitations to Photosynthesis In vivo

Ist Teil von

• Plant physiology (Bethesda), 2002-12, Vol.130 (4), p.1992-1998

Ort / Verlag

Rockville, MD: American Society of Plant Biologists

Erscheinungsjahr

2002

Link zum Volltext

Quelle

MEDLINE

Beschreibungen/Notizen

• CO2 transfer conductance from the intercellular airspaces of the leaf into the chloroplast, defined as mesophyll conductance ($g_{m}$), is finite. Therefore, it will limit photosynthesis when CO2 is not saturating, as in C3 leaves in the present atmosphere. Little is known about the processes that determine the magnitude of $g_{m}$. The process dominating $g_{m}$ is uncertain, though carbonic anhydrase, aquaporins, and the diffusivity of CO2 in water have all been suggested. The response of $g_{m}$ to temperature (10°C-40°C) in mature leaves of tobacco (Nicotiana tabacum L. cv W38) was determined using measurements of leaf carbon dioxide and water vapor exchange, coupled with modulated chlorophyll fluorescence. These measurements revealed a temperature coefficient (Q10) of approximately 2.2 for $g_{m}$, suggesting control by a protein-facilitated process because the Q10 for diffusion of CO2 in water is about 1.25. Further, $g_{m}$ values are maximal at 35°C to 37.5°C, again suggesting a protein-facilitated process, but with a lower energy of deactivation than Rubisco. Using the temperature response of $g_{m}$ to calculate CO2 at Rubisco, the kinetic parameters of Rubisco were calculated in vivo from 10°C to 40°C. Using these parameters, we determined the limitation imposed on photosynthesis by $g_{m}$. Despite an exponential rise with temperature, $g_{m}$ does not keep pace with increased capacity for CO2 uptake at the site of Rubisco. The fraction of the total limitations to CO2 uptake within the leaf attributable to $g_{m}$ rose from 0.10 at 10°C to 0.22 at 40°C. This shows that transfer of CO2 from the intercellular air space to Rubisco is a very substantial limitation on photosynthesis, especially at high temperature.