Photosynthesis and Photorespiration in Whole Plants of Wheat

Abstract

Wheat cv. Champlein was cultivated in a small phytotronic chamber. 18O2 was used to measure the O2 uptake by the plant, which was recorded simultaneously with the O2 evolution, net CO2 uptake, and transpiration. At normal atmospheric CO2 concentration, photorespiration, measured as O2 uptake, was as important as the net photosynthesis. The level of true O2 evolution was independent of CO2 concentration and stayed nearly equal to the sum of net CO2 photosynthesis and O2 uptake. At a given light intensity, O2 and CO2 compete for the reducing power produced at constant rate by the light reactions of photosynthesis.