Effect of carbon dioxide and temperature on photosynthetic CO2uptake and photorespiratory CO2evolution in sunflower leaves

摘要

Using an open gas-exchange system, apparent photosynthesis, true photosynthesis (TPS), photorespiration (PR) and dark respiration of sunflower (Helianthus annuusL.) leaves were determined at three temperatures and between 50 and 400 μl/l external CO2. The ratio of PR/TPS and the solubility ratio of O2/CO2in the intercellular spaces both decreased with increasing CO2. The rate of PR was not affected by the CO2concentration in the leaves and was independent of the solubility ratio of oxygen and CO2in the leaf cell. At photosynthesis-limiting concentrations of CO2, the ratio of PR/TPS significantly increased from 18 to 30°C and the rate of PR increased from 4.3 mg CO2dm-2h-1at 18°C to 8.6 mg CO2dm-2h-1at 30°C. The specific activity of photorespired CO2was CO2-dependent but temperature-independent, and the carbon traversing the glycolate pathway appeared to be derived both from recently fixed assimilate and from older reserve materials. It is concluded that PR as a percentage of TPS is affected by the concentrations of O2and CO2around the photosynthesizing cells, but the rate of PR may also be controlled by other fact