Carbon Fixation

LARA, MARIA V.; DRINCOVICH, MARÍA F.; ANDREO, CARLOS S.

Molecular Plant Biology

No Informado

Lugar: New York; Año: 2007; p. 1 - 1

In a general way, photosynthesis is the process by which green plants convert simple organic compounds, such as CO2, nitrate ions and water, into organic substances, such as carbohydrates and aminoacids, using the sun’s energy. The photosynthesis of plants and cyanobacteria created the biomass on earth, including the deposits of fossil fuels and atmospheric oxygen. This process also provides, ultimately, the entire biological world with energy. In this chapter we summarize the molecular, metabolic and physiological process with regards to carbon fixation, providing a thorough grounding in the subject to an advanced molecular level. We discuss the carbon metabolism in the so-called C3 plants, which fix inorganic carbon exclusively through the Calvin and Benson cycle. This primary process is analyzed in detail and related to photorespiration, the associated pathway that involves O2 consumption occurring in the light. As the efficiency of assimilation is strongly influenced by environmental conditions that increase the release of the fixed CO2 by photorespiration, different groups of plants have evolved to deal with this problem and with the loss of water associated with stomatal aperture. In this way, two of the main topics of this chapter are the C4 pathway and the plants that exhibit the Crassulacean Acid Metabolism (CAM plants), both of which utilize the C3 cycle. Furthermore, we analyze variations to the basic carbon fixation process represented by diverse photosynthetic metabolisms, such as C3-C4 intermediates, C4-like species and those plants that display transition between two types of metabolisms. The diversity on the assimilatory mechanisms is discussed in an evolutionary and ecophysiological context as well. We provide the basic knowledge for the understanding of the control of the CO2 fixation process and of the regulation of the expression of the enzymes involved. Finally, in the era of the engineering genetics, we try to make an overview of the different attempts done to improve photosynthesis and to introduce C4 genes into C3 plants.