Photosynthetic Oxygen Exchange in Attached Leaves of C4 Monocotyledons

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Abstract
Photosynthetic O2 evolution, O2 uptake and CO2 uptake by intact leaves from plants of the three C4 decarboxylation types were examined using mass-spectrometric gas-exchange and stable isotope techniques. All species showed a relative insensitivity of O2 uptake to CO2 concentration. The uptake rates observed were between 0.2 and 1 nmol O2 cm-2 S-1 at the CO2 compensation point. At ambient external CO2, NADP-malic enzyme type species showed the lowest average O2 uptake, phosphoenolpyruvate carboxykinase types the highest values, and NAD-malic enzyme types showed intermediate values for O2 uptake. These results are discussed in relation to the contributions to O2 uptake of ribulosebisphosphate oxygenase and photoreduction of oxygen.