Ultraviolet-B Radiation-Mediated Responses in Plants. Balancing Damage and Protection

Extract

Seven percent of the electromagnetic radiation emitted from the sun is in the UV range (200–400 nm). As it passes through the atmosphere, the total flux transmitted is greatly reduced, and the composition of the UV radiation is modified. Shortwave UV-C radiation (200–280 nm) is completely absorbed by atmospheric gases. UV-B radiation (280–320 nm) is additionally absorbed by stratospheric ozone and thus only a very small proportion is transmitted to the Earth's surface, whereas UV-A radiation (320–400 nm) is hardly absorbed by ozone (Fig. 1). In the past 50 years, the concentration of ozone has decreased by about 5%, mainly due to the release of anthropogenic pollutants such as chlorofluorocarbons (Pyle, 1996). Consequently, a larger proportion of the UV-B spectrum reaches the Earth's surface with serious implications for all living organisms (Xiong and Day, 2001; Caldwell et al., 2003).

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Elevated UV-B radiation (UV-B) has pleiotropic effects on plant development, morphology, and physiology, summarized in Table I. The morphological consequences of UV-B-supplemented white-light treatment include reduced growth, thickening of leaves and of cuticular wax layers. In addition, a lower photosynthetic capacity due to degradation of the D1 protein of photosystem II and reduced pollen fertility have been described for various plant species (Jansen et al., 1998; Caldwell et al., 2003).