C3, C4, and CAM photosynthesis.

Peter Miles
6 min readSep 2, 2020

Is C4 Rice the next Green Revolution?

C3, C4, and CAM refers to the different photosynthetic pathways that are present in individual plant species and are the result of adapting to various climatic conditions.

C4 hot season growing grass, kangaroo grass, Themeda triandra. Image — Peter Miles.

C3 and C4 indicates the number of carbon atoms in the sugar molecules produced by the photosynthesis. CAM is Crassulacean acid metabolism in which carbon dioxide CO2 is fixed at night.

Generally, C3 plants are suited to cool, moist conditions, C4 to hot and dry, and CAM to arid conditions.


Kranz anatomy or large bundle sheath cells around the veins, found in C4 plants.

Malate, malic acid, CO2 transported as malate to the bundle sheath cells in C4 plants.

Phosphoenolpyruvate (PEP) carboxylase, an enzyme used to fix CO2 in C4 plants and works well in temperatures above 15 degrees C.

Rubisco, an enzyme used in the fixing of CO2 in C3 plants and works well in temperatures below 15 degrees C.

Stomata, leaf openings which are able to regulate diffusion of water vapour, carbon dioxide and oxygen.

C4 plant, drawing of leaf anatomy:

Bundle sheath cells (circle of shaded cells around a vein) Mesophyll cells (unshaded cells surrounding bundle sheath cells) Stoma (openings in base of leaf).

Most plants have C3 photosynthesis, eg. rice, wheat, barley and oats; tropical grasses for example are C4, sorghum, sugarcane and corn (maize); and CAM plants such as pineapple, agave and prickly pear cactus are found in very dry conditions.

The terms C3 and C4 are also often used in describing grasses, such as the increasingly cultivated Australian indigenous grasses, for example the C3 cool to warm season growing species weeping rice grass, wallaby and spear grasses and C4 hot season growth kangaroo grass and windmill grass. Commonly used C4 sports turf grasses are kikuyu, buffalo and couch grasses and grow in hot conditions, while other common turf grasses rye and bent grass are C3 growing in cool conditions.

In C3 or the Calvin-Benson pathway of photosynthesis (named after the biochemists who discovered it in 1950 at the University of California, Berkeley), three…

Peter Miles

45 years in Environmental Science, B.Env.Sc. in Wildlife & Conservation Biology. Writes on Animals, Plants, Soil & Climate Change. environmentalsciencepro.com