Effects of Ultraviolet Radiation on Cyanobacteria and their Protective Mechanisms

Enhanced solar ultraviolet radiation (UVR) due to stratospheric ozone depletion is a major stress factor for many phototrophic organisms in aquatic and terrestrial ecosystems (Franklin and Forster, 1997). UVR includes the wavelengths below those visible to the human eye. According to the CIE (Commission Internationale de l’Eclairage), the spectral range is divided into three wavebands: 315–400 nm UVA, 280–315 nm UVB and 190–280 nm UVC. UVA is not attenuated by ozone, and hence its fluence rate will be unaffected by any ozone layer reduction reaching aquatic and terrestrial organisms. Increases in UVB have been particularly reported in Antarctica (McKenzie et al., 2003) and the adjacent geographic regions (southern parts of South America and Australia) (Buchdahl, 2002; Deschamps et al., 2004), as well as in more recent years in the Arctic region (Knudsen et al., 2005). UVB exposure is potentially harmful to all living organisms, but especially to photosynthetic organisms due to their requirement for light. UVB represents less than 1% of the total solar radiation reaching the earth’s surface, because it is absorbed partly by the ozone layer. It is particularly this waveband, which is influenced by changing stratospheric ozone concentrations caused by anthropogenic emissions of greenhouse gases, such as chlorinated fluorocarbons (Fraser et al., 1992).