The biochemical pathway of CAM photosynthesis begins during night. The stomata of CAM plants are open at night so the formation of malic acid take place in the night and it get accumulated in the cell vacuole and later it breaks down in day. The PEP carboxylase mediates the conversion of carbon dioxide and PEP to malic acid. During the day time malic acid breakdown back to carbon dioxide when they are needed for Calvin cycle.
Malic acid is stored in the vacuole through the night, it act as a source of carbon dioxide for the C3 cycle. At the arrival of daytime the stomata closes. The malic acid is then transported from the vacuole to the cytoplasm where it is break down; from there the carbon dioxide enter the chloroplast for the C3 cycle.
