Ultraviolet-B radiation: From stressor to regulatory signal

Following the discovery of ozone layer depletion in the late 1980s, large numbers of studies investigatedthe effects of ambient and/or enhanced levels of ultraviolet-B (UV-B) radiation on plants, animals,humans and microorganisms. Initial studies reported severe, inhibitory UV effects on plantgrowth and development, and these were associated with damage to genetic material and the photosyntheticmachinery. This led to a strong perception that UV-radiation is harmful for plants. Since thattime, a conceptual U-turn has taken place in the way that UV-B effects are perceived. Under realisticUV-B exposure conditions, accumulation of UV-mediated damage is a relatively rare event. Instead, itis now recognized that UV-B is a specific environmental regulator that controls cellular, metabolic,developmental and stress-protection processes in plants, through UV-B-specific and non-specific UVsignalling pathways. UV-B regulated signalling pathways control, among others, the morphology,nutritional value, pest and disease tolerance, and hardiness of plant tissues. As a consequence, UV-Bradiation can impact on trophic relationships and ecosystem function, but is also a potentially valuabletool for a more sustainable agriculture.