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7.4: C4 Plants

The Calvin Cycle is the means by which plants assimilate carbon dioxide from the atmosphere, ultimately into glucose. Plants use two general strategies for doing so. The first is employed by plants called C3 plants (most plants) and it simply involves the pathway described above. Another class of plants, called C4 plants employ a novel strategy for concentrating the \(\text{CO}_2\) prior to assimilation. C4 plants are generally found in hot, dry environments where conditions favor the wasteful photorespiration reactions of RUBISCO, as well as loss of water. In these plants, carbon dioxide is captured in special mesophyll cells first by phosphoenolpyruvate (PEP) to make oxaloacetate. The oxaloacetate is converted to malate and transported into bundle sheath cells where the carbon dioxide is released and it is captured by ribulose-1,5-bisphosphate, as in C3 plants and the Calvin Cycle proceeds from there. The advantage of this scheme is that it allows concentration of carbon dioxide while minimizing loss of water and photorespiration.

Figure 7.4.1: C4 Plant Cycle

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