Crassulacean acid metabolism, also known as
CAM photosynthesis, is a
carbon fixation pathway that evolved in some
plants as an adaptation to
arid conditions. In a plant using full CAM, the
stomata in the leaves remain shut during the day to reduce
evapotranspiration, but open at night to collect
carbon dioxide . The is stored as the four-carbon acid
malate in
vacuoles at night, and then in the daytime, the malate is transported to
chloroplasts where it is converted back to , which is then used during
photosynthesis. The pre-collected is concentrated around the enzyme
RuBisCO, increasing
photosynthetic efficiency. This metabolism was first studied in plants of the Crassulaceae family. These mainly include
succulents. The first time it was studied,
Crassula was used as a model organism.