Crassulacean acid metabolism occurs in succulent
plants and gets completed in two phases :
Phase I : (a) Stomata are open at night. CO2 is absorbed from outside. With the help of PEP carboxylase, it is immediately fixed.
(b) The acceptor is Phosphoenol pyruvate or PEP.
© Malic acid is end product of dark fixation of CO2. It is stored inside cell vacuoles.
Phase II: (a) During day time, stomata are closed. However, light is available for photosynthesis.
(b) Malic acid moves out of the cell vacuoles.
© It is decarboxylated with the help of malic enzyme.
(d) Pyruvate is produced. It is metabolised.
Malic acid (malate) + NADP+ malic/Enzyme-------> Pyruvate + CO2 + NADPH
(e) The released CO2 is fixed again through Calvin cycle with the help of RuBP a’nd Rubisco.
(f) Crassulacean plants have developed a unique
mechanism to perform photosynthesis without much lose of water.