C3 Plants

Abstract

Photosynthesis is the basic process of primary carbon assimilation in plants. This article is an overview of the physiology and biochemistry of photosynthesis, with focus on C3 pathway or Calvin-Benson-Bassham cycle. During C3 pathway, the first product of carboxylation is 3-phosphoglycerate (PGA), a 3-carbon compound. There are two adjuncts to Calvin cycle, namely the C4 pathway or Crassulacean Acid Metabolism, both of which act as CO2-concentrating mechanisms, to raise the level of CO2 at the vicinity of Rubisco in chloroplasts. Plants possessing only the Calvin cycle, called C3 plants, constitute almost 90% of the Embryophyta (land plants). The Calvin cycle consists of three phases: (1) formation of PGA from ribulose-1,5-bisphosphate (RuBP) and CO2 (carboxylation phase); (2) reduction of PGA to triose-P (reduction phase); and (3) regeneration of the CO2 acceptor, RuBP, from triose-P (regeneration phase). The cycle is regulated in several ways: autocatalysis, flux control, modulation by light of enzymes, carbon partitioning, and interaction with mitochondria. Future work on Calvin cycle with model organisms, such as Arabidopsis thaliana, rice, and Chlamydomonas would be of great benefit.