High CO2 partial pressure effects on dark and light CO2 fixation and metabolism in Vicia faba leaves.

Stomatal opening on Vicia faba can be induced by high CO2 partial pressures (10.2%) in dark as well as in light. Stomatal aperture was measured in both cases with a hydrogen porometer. The distribution of (14)C among early products of photosynthesis was studied. Comparisons are made with carboxylations occurring when stomata were open in the dark with CO2-free air and in light with 0.034% CO2. Results showed that in high CO2 partial pressure in light, less radioactivity was incorporated in Calvin cycle intermediates and more in sucrose. β carboxylations and photorespiration seemed to be inhibited. In the dark in both CO2 conditions, (14)C incorporation was found in malate and aspartate but also in serine and glycerate in high CO2 conditions. In light these changes in metabolic pathways may be related with the deleterious effects recorded on leaves after long-term expositions to high partial pressure of CO2.