6 - The C4 Pathway

Abstract

Terrestrial plants are conveniently classified as C3 plants, C4 plants, and crassulacean acid metabolism plants based on differences in photosynthetic carbon metabolism. The chapter describes the biochemistry and regulation of C4 photosynthesis. C4 plants are recognized for having higher rates of leaf photosynthesis than C3 plants at high light intensities, atmospheric and respective temperature optima, because of the CO2- concentrating mechanism in C4. C4 plants have a greater photosynthetic capacity and are more productive than C3 plants. Photosynthetic reactions and related processes catalyzed by C4 mesophyll preparations exhibit relatively high temperature optima, as CO2 assimilation by whole leaves. Considerable inter- and intracellular metabolite transport is required during C4 photosynthesis based on the spatial compartmentation of enzymes. The chapter discusses the characteristics and regulation of a number of enzymes of the C4 cycle, including PEP carboxylase and C4 acid decarboxylases. C4 photosynthesis is very responsive to light.