Crassulacean acid metabolism or CAM cycle

It occurs mostly in succulent plants which grow under semi-arid conditions. This mode of CO2 fixation takes place during the night (dark) because the stomata of the leaves of these plants remain open only during the night. These plants absorb CO2 during night and convert it into malic acid which is then stored in vacuoles. During daytime (light) decarboxylation of malic acid takes place and CO2 is released. This CO2 is utilized by C3-cycle. The cycle was first observed in the plants belonging to the family Crassulaceae e.g. Bryophyllum, Sedum, Kalanchoe, etc. It was named Crassulacean Acid Metabolism (CAM). Similar metabolism has been reported in plants belonging to the following families:

1. Dicot Families: Crassulaceae e.g. (sedum, Opuntia) Azoaceae, Asclepiadaceae, Caryophyllaceae, Chenopodium, compositae, convolvulaceae, Euphoebiaceae, Vitaceae, etc.

2. Monocot Families: Liliaceae, Orchidaceae.
3. Pteridophytes: Polypodiaceae.