Photosynthetic Oxygen Exchange in Attached Leaves of C₄ Monocotyledons

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.