Crassulacean acid metabolism: a cause or consequence of oxidative stress in planta?

Niewiadomska, E; Borland, AM

doi:10.1007/978-3-540-72954-9_10

Crassulacean acid metabolism: a cause or consequence of oxidative stress in planta?

Lookup NU author(s): Emerita Professor Anne Borland

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Abstract

The photosynthetic specialization of crassulacean acid metabolism (CAM) is typically found in plants growing in environments where water and/or CO2 is limiting and, by analogy, where irradiance and daytime temperatures may be high. Such abiotic actors are known to lead to the generation of reactive oxygen species (ROS) in planta which can elicit potentially damaging oxidative stress and/or act as signals for engaging mechanisms that ameliorate oxidative stress. It has been proposed that CAM prevents the production of ROS, since the daytime CO2 concentrating effect prevents overenergization of the photosynthetic machinery under water-limited conditions. However, CAM per se has the potential to elevate the oxidative burden in planta as a consequence of sustained electron transport behind closed stomata, which can elevate internal O2 concentrations to around 42%. This review considers and discusses evidence for the photoprotective function of CAM, alongside considerations of the extent of photorespiration and other potential sinks for O2 consumption. Anti-oxidant metabolism in CAM species is also reviewed and considered along with the potential role of ROS in triggering the induction or up-regulation of this photosynthetic specialization in limiting environments. The overall aim of the review is to assess whether or not CAM alleviates the oxidative burden in plants exposed to potentially limiting environmental conditions.