SINGLE-CELL C4 PHOTOSYNTHESIS VERSUS THE DUAL-CELL (KRANZ) PARADIGM

Abstract

▪ Abstract The efficiency of photosynthetic carbon assimilation in higher plants faces significant limitations due to the oxygenase activity of the enzyme Rubisco, particularly under warmer temperatures or water stress. A drop in atmospheric CO2 and rise in O2 as early as 300 mya provided selective pressure for the evolution of mechanisms to concentrate CO2 around Rubisco in order to minimize oxygenase activity and the resultant loss of carbon through photorespiration. It is well established that a carbon-concentrating mechanism occurs in some terrestrial plants through the process of C4 photosynthesis. These plants are characterized as having Kranz-type leaf anatomy, with two structurally and biochemically specialized photosynthetic cell types, mesophyll and bundle sheath, that function coordinately in carbon assimilation. C4 photosynthesis has evolved independently many times with great diversity in forms of Kranz anatomy, structure of dimorphic chloroplasts, and biochemistry of the C4 cycle. The most d...