Journal Article

Calibration of Simultaneous Measurements of Photosynthetic Carbon Dioxide Uptake and Oxygen Evolution in Leaves

Vello Oja, Hillar Eichelmann and Agu Laisk

in Plant and Cell Physiology

Published on behalf of Japanese Society of Plant Physiologists

Volume 48, issue 1, pages 198-203
Published in print January 2007 | ISSN: 0032-0781
Published online January 2007 | e-ISSN: 1471-9053 | DOI: http://dx.doi.org/10.1093/pcp/pcl056
Calibration of Simultaneous Measurements of Photosynthetic Carbon Dioxide Uptake and Oxygen Evolution in Leaves

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  • Biochemistry
  • Molecular and Cell Biology
  • Plant Sciences and Forestry

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The stoichiometric ratio of O2 evolution to CO2 uptake during photosynthesis reveals information about 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. Since the O2/CO2 exchange ratio is ∼1, small differences are important. Thus, these gas exchange measurements need precise calibration. In this work, we describe a new calibration procedure for 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 an error (relative standard deviation, RSD) of <1%. Measurements on a sunflower leaf resulted in an O2/CO2 ratio between 1.0 and 1.03 under different CO2 concentrations and light intensities, in the presence of an ambient O2 concentration of 20–50 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: Alternative electron transport; Carbon dioxide; Oxygen; Photosynthesis

Journal Article.  3658 words.  Illustrated.

Subjects: Biochemistry ; Molecular and Cell Biology ; Plant Sciences and Forestry

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