Crassulacean Acid Metabolism (CAM) in Kalanchoë: Changes in Intercellular CO2 Concentration During a Normal CAM Cycle and During Cycles in Continuous Light or Darkness

In the crassulacean acid metabolism (CAM) plant Kalanchoë daigremontiana, the internal CO2 concentrations were measured throughout CAM cycles by gas chromatography. Under normal dark-light cycles, the internal CO2 concentration was near that of the ambient air and increased up to 0.5% during the phase of maximum malate decarboxylation. A sharp increase in internal CO2 concentration occurring after the first 12 h of the cycle was exhibited by the plants both when there was a normal day-night cycle and when the night was replaced by illumination, and also when the light period was replaced by darkness. Thus, the increase in internal CO2 in the morning does not appear to be primarily determined by a light-on signal or by alterations of temperature rather than by inherent factors of the leaves. This view is supported further by a steep increase in (14)CO2 production from labeted malate occurring during extended darkness at a time when the light period would normally begin. The results are discussed in particular in relation to of how CAM can control stomata movement.