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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. [ABSTRACT FROM AUTHOR]

Salt stress can induce ionic stress and osmotic stress in plant cells. A direct result of these primary effects is the enhanced accumulation of reactive oxygen species (ROS) that are harmful to plant cells at high concentrations. To cope with the oxidative stress resulting from the ROS, higher plants have developed a complex scavenging system including enzymatic and non-enzymatic (antioxidants) system. In plant cells, specific ROS producing and scavenging systems are found in different organelles such as chloroplasts, mitochondria, and peroxisomes; and the ROS-scavenging pathways from different cellular compartments are coordinated. Relatively low levels of ROS can be used for signaling molecules to control abiotic stress responses. Coordinated work of ROS-scavenging pathways from different cellular compartments in modulating the level of ROS in cells preventing cellular damage and controlling ROS signaling may play a key role in plant salt tolerance. Here we attempt to summarize the recent researches on ROS and the mechanism of salt tolerance of plants under salt stress, and we also propose some perspectives involved in ROS and plant salt tolerances in the future. [ABSTRACT FROM AUTHOR]

Plants sense environmental signals by various sensory mechanisms distributed over all subcellular compartments. Plasma membrane integrated receptors sense pathogens, excess salinity, hormonal signals and light. Through membrane transporters, soluble environmental signals are imported into the cytosol, where the ion, redox and pH homeostasis is controlled. Endomembranes and microbodies form small cellular sub-compartments involved in environmental sensing and signal transduction. Light sensing, which strongly controls plant metabolism, is separated into qualitative light sensing by photoreceptor proteins at the plasma membrane and in the cytosol and quantitative light sensing through photosynthesis. Embedded into the cytosol, besides light sensing, the organelles mainly integrate environmental signals, respond to cytosolic changes and trigger metabolite fluxes, the energy supply and developmental programmes such as cell death. Covering a selection of environmental sensing mechanisms, recent insights into the diversity of subcellular sites and mechanisms of environmental sensing will be reviewed. [ABSTRACT FROM AUTHOR]

One of the great fascinations of the genus Clusia is that its single leaf morphotype (Sect. 2.1) expresses different photosynthetic physiotypes. Often different photosynthetic types are even expressed by the same species and even in clones of vegetatively propagated plants or in different leaves of single individual plants depending on environmental conditions. The photosynthetic types observed among Clusias are based on the modes of C3-photosynthesis and of crassulacean acid metabolism (CAM) and its variants. Figure 8.1 presents a schematic overview of the basic features of the three to four different photosynthetic physiotypes found among Clusias. Figures 8.2 and 8.3 show typical patterns of photosynthetic CO2-gas exchange for different modes of photosynthesis expressed among four different species under identical conditions in a phytotron (Fig. 8.2) and for different modes of photosynthesis expressed in one species, Clusia minor L., under different conditions (Fig. 8.3), respectively. [ABSTRACT FROM AUTHOR]