The Molecular Biology of Plants Exposed to Ultraviolet-B Radiation and the Interaction with Other Stresses

Abstract

The stratospheric ozone layer acts as a protective shield to remove harmful ultraviolet-B radiation (particularly UV-B:280--320 nm). The progressive global depletion of this ozone layer is, however, leading to increased levels of UV-B radiation reaching the earth's surface. This increase will inevitably continue into the next century with potentially deleterious consequences for agriculture, horticulture and forestry. Studies of UV-B radiation effects on plants have shown a wide range of responses. Some species are particularly sensitive and show signs of damage at moderate increases in UV-B irradiance, while other species show no response. Amongst the more susceptible species are agriculturally important crops from temperate latitudes, such as pea, although tropical crops including rice can also suffer damage from increased UV-B radiation. The specific effects upon plants include inhibition of photosynthesis, loss of fresh and dry weight, changes in assimilate partitioning, alteration in pigment biosynthesis and effects upon flowering and reproduction. These responses would clearly lead to substantial changes in plant communities and to significant losses in agricultural productivity. A major factor that determines the extent of these changes is the interaction between UV-B radiation and other environmental parameters. Thus, any prediction as to the consequences of increased UV-B can only be realistic in the context of interactions with other stresses. One way to predict the plant response is to obtain an understanding of the molecular changes induced by UV-B stress and how they are controlled. In this chapter the molecular biology of UV-B responses is described. Two major UV-B sensitive processes are focussed on, photosynthesis and the biosynthesis of protective pigments. In addition, the influence of other environmental stresses on UV-B induced responses will be discussed.