Effect of Oxygen on Photosynthesis, Photorespiration and Respiration in Detached Leaves. II. Corn and other Monocotyledons.

The effect of O(2) on the CO(2) exchange of detached leaves of corn (Zea mays), wheat (Triticum vulgare), oats (Avena sativa), barley (Hordeum vulgare), timothy (Phleum pratense) and cat-tail (Typha angustifolia) was measured with a Clark oxygen electrode and infrared carbon dioxide analysers in both open and closed systems.Corn leaves did not produce CO(2) in the light at any O(2) concentration, as was shown by the zero CO(2) compensation point and the absence of a CO(2) burst in the first minute of darkness. The rate of photosynthesis was inhibited by O(2) and the inhibition was not completely reversible. On the other hand, the steady rate of respiration after a few minutes in the dark was not affected by O(2).These results were interpreted as indicating the absence of any measurable respiration during photosynthesis. Twelve different varieties of corn studied all responded to O(2) in the same way.The other 5 monocotyledons studied did produce CO(2) in the light. Moreover, the CO(2) compensation point increased linearly with O(2) indicating a stimulation of photorespiration.The implications of the lack of photorespiration in studies of primary productivity are discussed.