Abstract
The effect of O2 on the CO2 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 CO2 in the light at any O2 concentration, as was shown by the zero CO2 compensation point and the absence of a CO2 burst in the first minute of darkness. The rate of photosynthesis was inhibited by O2 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 O2.
These results were interpreted as indicating the absence of any measurable respiration during photosynthesis. Twelve different varieties of corn studied all responded to O2 in the same way.
The other 5 monocotyledons studied did produce CO2 in the light. Moreover, the CO2 compensation point increased linearly with O2 indicating a stimulation of photorespiration.
The implications of the lack of photorespiration in studies of primary productivity are discussed.
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