C4 photosynthesis

SummaryThe number of humans on earth is increasing, generating concerns about food security and spurring efforts throughout the world to increase the productivity of crops. If a way could be found to increase the yield of crops by, say, 20%, it would have immense impact on global food supplies. Fortunately, evolution has already crafted such a mechanism, known as C4 photosynthesis. The C4 pathway is in effect a turbocharger for the more conventional C3 pathway. Just as a turbocharger improves performance of an engine by forcing more air into the manifold, C4 improves photosynthetic performance by forcing CO2 into the standard C3 photosynthetic apparatus. The added efficiency of this mechanism is obvious at a global level. Only about 3% of flowering plant species use the C4 pathway, but this relative handful of species account for 23% of the carbon fixed (primary productivity) in the world. The pathway occurs in several of the world’s major crops, notably maize (corn) and sorghum, and in many of the species in use as biofuels, most importantly sugar cane; all of these are grasses in the family Poaceae. If a major C3 crop such as rice could be bred to use the C4 pathway, the economic impact would be immense