Transport across the vacuolar membrane in CAM plants

Close metabolic parallels exist between the processes of CO2 assimilation in C4 plants and in CAM plants. In both types of plant, a C4 cycle starts with the fixation of CO2 (as HCO3 −) by phosphoenolpyruvate carboxylase (PEPC) and concludes with the release or CO2 by decarboxylation of a C4 dicarboxylate anion (malate or aspartate). This C4 cycle is an ancillary pathway, in the sense that it does not mediate the net fixation of atmospheric CO2. It simply passes on this CO2, at greatly elevated concentration, to ribulose 1,5-bisphosphate carboxylase/oxygenase (RUBISCO) for assimilation through the standard C3 photosynthetic carbon reduction cycle.