Crassulacean acid metabolism

Crassulacean acid metabolism (CAM) is a photosynthetic pathway in which plants absorb carbon dioxide mainly at night, store it as organic acids, and release it for daytime photosynthesis. Separating carbon uptake from sugar production in time reduces water loss.

Stomata: Microscopic pores in plant surfaces that regulate gas exchange and water loss. CAM plants usually open these pores at night, when evaporation is lower.
C4 carbon fixation: A photosynthetic strategy that initially fixes carbon dioxide into four-carbon compounds before concentrating it near Rubisco. Like CAM, it uses phosphoenolpyruvate carboxylase to concentrate carbon dioxide, but separates steps across cells.
Crassulaceae: A flowering-plant family that includes many succulents and gave Crassulacean acid metabolism its name. Several familiar members display CAM, though the pathway occurs across many plant families.
C4 photosynthesis: A photosynthetic pathway that concentrates carbon dioxide in specialized cells before its fixation by Rubisco. C4 separates initial and final carbon fixation spatially, whereas CAM separates them mainly by time.
CAM evolution: The evolutionary history and repeated emergence of Crassulacean acid metabolism in plants. Its scattered distribution across plant lineages suggests CAM arose multiple times.
Phosphoenolpyruvate carboxylase: An enzyme that fixes bicarbonate onto phosphoenolpyruvate to form oxaloacetate. It captures carbon dioxide-derived bicarbonate during CAM’s nocturnal phase.
C3 carbon fixation: The common photosynthetic pathway in which Rubisco fixes carbon dioxide directly in the Calvin cycle. CAM modifies this pathway by supplying the Calvin cycle with carbon dioxide stored overnight.
Agave: A genus of succulent plants native to the Americas, many of which use CAM photosynthesis. Agave illustrates how CAM supports productive growth in dry environments.
C3 photosynthesis: A photosynthetic pathway in which Rubisco fixes carbon dioxide directly into a three-carbon product. Unlike CAM, C3 plants generally take in most carbon dioxide during daylight.
CAM photosynthesis in crops: Research into improving or engineering crop plants with Crassulacean acid metabolism. It explores whether CAM’s water efficiency can be combined with high crop yields.

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