crassulacean acid metabolism

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A method of carbon dioxide fixation that conserves water in certain succulent, drought-resistant plants. At night, when the external temperature and therefore the evaporation rate are low, the leaf stomata open allowing carbon dioxide to enter leaf cells where it is incorporated in an organic acid. During the day the stomata remain closed, conserving moisture, while the acids are decarboxylated and the carbon dioxide is used for the dark reactions of photosynthesis. The initial fixation of carbon dioxide results in the formation of compounds with four carbon atoms; this process uses the enzyme phosphoenol pyruvate carboxylase, as in C4 photosynthesis (see C4 plants). In CAM, however, there is no spatial movement of this product prior to processing by the Calvin cycle. This pathway of carbon fixation was first observed in members of the Crassulaceae, hence the name.

Subjects: Plant Sciences and Forestry — Ecology and Conservation.

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