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Plant and Cell Physiology Advance Access published online on December 13, 2006
Plant and Cell Physiology, doi:10.1093/pcp/pcl056
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© The Author 2006. Published by Oxford University Press on behalf of Japanese Society of Plant Physiologists. All rights reserved. For permissions, please email: journals.permissions@oxfordjournals.org

Calibration of simultaneous measurements of photosynthetic carbon dioxide uptake and oxygen evolution in leaves

Vello Oja, Hillar Eichelmann and Agu Laisk

Tartu ülikooli Molekulaar- ja Rakubioloogia Instituut, Riia tn. 23, Tartu, 51010, Estonia;

Author to whom correspondence should be addressed: A. Laisk, Institute for Molecular and Cell Biology, Tartu University, 23 Riia St. Tartu 51010, Estonia, Phone: +372 736 6021, FAX: +372 742 0286, Email: alaisk{at}ut.ee


  Abstract

The stoichiometric ratio of O2 evolution to CO2 uptake during photosynthesis reveals information about the reductive metabolism, including the reduction of alternative electron acceptors, such as nitrite and oxaloacetate. Recently we reported that in simultaneous measurements of CO2 uptake and O2 evolution in a sunflower leaf O2 evolution changed by 7% more than CO2 uptake when light intensity was varied (Laisk, A. et al. Plant Cell Physiol 47: 972-983). Since the O2/CO2 exchange ratio is about one, small differences are important. Thus, these gas exchange measurements need precise calibtation. In this work we describe a new calibration procedure of such simultaneous measurements, based on the changes of O2 concentration caused by the addition of pure CO2 or O2 into a flow of dry air (20.95% O2) through one and the same capillary. The relative decrease in O2 concentration during the addition of CO2 and the relative increase in O2 concentration during the addition of O2 allowed us to calibrate the CO2 and O2 scales of the measurement system with the error (relative standard deviation, R.S.D) of less than 1%. Measurements on a sunflower leaf resulted in the O2/CO2 ratio between 1.0 and 1.03 under different CO2 concentrations and light intensities, in the presence of the ambient O2 concentration of 20 to 50 µmol mol–1. This shows that the percentage use of reductive power from photochemistry in synthesis of inorganic or organic matter other than CO2 assimilation in the C3 cycle is very low in mature leaves and, correspondingly, the reduction of alternative acceptors is a weak source of coupled ATP synthesis.

Keywords: photosynthesis - carbon dioxide - oxygen - alternative electron transport


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A. Laisk, H. Eichelmann, V. Oja, E. Talts, and R. Scheibe
Rates and Roles of Cyclic and Alternative Electron Flow in Potato Leaves
Plant Cell Physiol., November 1, 2007; 48(11): 1575 - 1588.
[Abstract] [Full Text] [PDF]


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