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Metabolic
Maize, sugarcane, sorghum, many grasses
C4 Photosynthesis
Spatial separation of initial CO₂ fixation and Calvin cycle to concentrate CO₂.
Overview
C4 photosynthesis spatially separates initial carbon fixation from the Calvin cycle between mesophyll and bundle sheath cells. In mesophyll cells, PEP carboxylase fixes CO₂ into oxaloacetate (4-carbon compound), which is converted to malate or aspartate and transported to bundle sheath cells. There, CO₂ is released and refixed by RuBisCO at high concentration, minimizing photorespiration.
Cellular Location
Mesophyll cells → Bundle sheath cells
Clinical Significance
Eliminates photorespiration; higher efficiency in hot/dry climates; C4 rice project aims to engineer this into rice for global food security.