Standard Article

Crassulacean Acid Metabolism

  1. Ulrich Lüttge

Published Online: 15 DEC 2008

DOI: 10.1002/9780470015902.a0001296.pub2



How to Cite

Lüttge, U. 2008. Crassulacean Acid Metabolism. eLS. .

Author Information

  1. Darmstadt University of Technology, Darmstadt, Germany

Publication History

  1. Published Online: 15 DEC 2008

This is not the most recent version of the article. View current version (16 NOV 2015)


Crassulacean acid metabolism (CAM) is a carbon dioxide acquisition, carbon dioxide transient storage and carbon dioxide concentrating mechanism of plants based on organic acid synthesis. In this variant of photosynthesis carbon dioxide can be fixed nocturnally in the dark and is used during the day for assimilation in the light. This has arisen polyphyletically many times during evolution. It is an ecophysiological adaptation that allows carbon dioxide acquisition with exceptionally economic use of water. It is regulated in a natural night/day rhythm but can also oscillate freely under the control of circadian biological clocks.

Key concepts

  • Metabolic mechanisms concentrating carbon dioxide internally in plants are important for photosynthesis at the low external carbon dioxide concentration in the present atmosphere.

  • Rearranged internal management of available metabolic housekeeping functions can generate new metabolic options of adaptive value.

  • Generation of isoforms of housekeeping enzymes can facilitate polyphyletic evolution of new metabolic pathways.

  • Circadian oscillations can be controlled by different biological clocks, which are feedback related to each other and present in many copies.

  • Flexibility in the expression of metabolic pathway variants facilitates adaptation under variable stress situations.

  • Stress adaptation in plants is for survival and mostly not for high productivity.


  • circadian rhythmicity;
  • carbon dioxide acquisition;
  • malate;
  • phosphoenolpyruvate carboxylase;
  • vacuolar H+ ATPase