Effect of Different CO₂ Regimes on the Induction of Crassulacean Acid Metabolism in Mesembryanthemum crystallinum L

Abstract

Induction of crassulacean acid metabolism (CAM) in Mesembryanthemum crystallinum in response to high salinity was studied in plants grown in different CO₂ regimes to determine whether the induction of CAM could be controlled by CO₂ supply in the light and dark; a possible consequence of stomatal closure in response to water stress. The activity of extractable phosphoenolpyruvate carboxylase (EC 4.1.1.31) and the nocturnal change in malate content were followed at frequent intervals after onset of the treatments. The results suggest that the initial event during the induction of CAM is a change in the biochemical apparatus, indicated by the activity of phosphoenolpyruvate carboxylase, which then leads to the day/night fluctuations of malate synthesis typical of CAM. This initial step is not controlled by the availability of CO₂ in the light or dark.