C4 plants adaptation to high levels of CO2 and to drought environments

LARA, MARÍA VALERIA; ANDREO, CARLOS SANTIAGO

Abiotic Stress in Plants - Mechanisms and Adaptations

Croacia

Lugar: Rejica; Año: 2011; p. 415 - 428

C4 Plants Adaptation To High Levels Of CO2 And To Drought Environments     Photosynthesis is the primary physiological process that drives plant growth and crop productivity and influences many other plant processes. It is also strongly affected by environmental stress. Its study becomes increasingly important in the context of assessing the impact of climate change on agro-ecosystem function. Atmospheric carbon is fixed by the enzyme ribulose-1, 5-bisphosphate carboxylase/oxygenase (Rubisco) in the chloroplast of photosynthetic cells. In the majority of plants (C3 photosynthesis), this process occurs in a single photosynthetic cell type. Because the specificity of Rubisco for CO2 and the solubility of CO2 relative to O2 decline with increases in temperature, photorespiration as a proportion of photosynthesis increases with temperature. The reduction in efficiency associated with photorespiration and the energetic costs of recycling its products has been estimated to limit the performance of C3 photosynthesis by as much as 30% in hot arid conditions. On the other hand, C4 photosynthesis is characterized by a biochemical CO2 pump that increases the concentration of CO2 around Rubisco to ca. 10  current atmospheric concentrations. For the most cases, the C4 cycle takes place in a coordinated manner in two types of photosynthetic cells: the mesophyll and the bundle sheath cells. The C4 system is more efficient under some environmental conditions as it increases the concentration of CO2 in bundle sheath cells suppressing the oxygenase activity of RuBisCO and thus, photorespiration. In addition, C4 plants use water and nitrogen more efficiently than C3 species. The changes in global climate include increase in atmospheric CO2 concentrations with the concomitant rise in temperatures and modifications in the precipitation patterns. Therefore climate change affects photosynthetic carbon assimilation and thus plant growth and development. Many studies have been conducted on the impacts of water availability, temperature, soil nutrition and ozone in plants. Regarding the effects on photosynthesis of rising CO2 both positive and negative responses have been described. In this respect, extensive work has been carried out in C3 plants. Although photosynthesis is easily saturated at normal ambient CO2 levels, the impact of rises in CO2 concentrations has been less investigated. Nevertheless, C4 plants do respond to elevated CO2. In the present chapter a revision of the effect of variable CO2 levels as well as variations in other interacting environmental factors, such as temperature, water availability and nutrients is presented.