Plant Physiology - Lecture Notes - O. M. Tarnopilska 2019

4. Photosynthesis
4.8 Crassulacean Acid Metabolism (CAM) Photosynthesis

In succulents (cacti and plants of the family Crassulaceae), the processes of Photosynthesis are separated not in space, unlike other C4 plants, but in time.

This type of photosynthesis is known as the CAM (crassulacean acid METABOLISM) pathway.

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Figure 4.6 - The Hatch-Slack cycle (C4 photosynthetic pathway).

CW - Cell wall (after V. V. Polovyi)

Stomata are generally closed during the day, which prevents Water loss through Transpiration, and open at night. In the dark, CO2 enters the leaves, where phosphoenolpyruvate carboxylase attaches it to phosphoenolpyruvic acid, producing oxaloacetic acid. This acid is reduced by NADPH-dependent malate dehydrogenase to malic acid, which accumulates in the vacuoles. During the day, malic acid moves from the vacuole into the Cytoplasm, where it undergoes decarboxylation to release CO2 and pyruvic acid. CO2 then diffuses into the Chloroplasts and enters The Calvin Cycle (Fig. 4.7).



Last update: 07/08/2026

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