The effects of UVB radiation on charophycean algae and bryophytes

This thesis reports on the effects of UVB radiation on charophycean algae and bryophytes. Due to thinning of the ozone layer, more UVB radiation is reaching the earth surface. UVB radiation affects life on earth. Since the discovery of the ozone hole many studies focused on the effects of UV(B) radiation on terrestrial and marine organisms. Studies that focused on the effects on plants showed direct UVB damage to DNA, proteins, lipids, pigments and phytohormones, which may lead to altered growth and morphology. However, many plants are able to avoid damage due to harmful UVB radiation (e.g. by production of UV screens) or to repair the UV-induced damage that had occurred, thus decreasing the sensitivity of an organism to UVB radiation. It is expected that the sensitivity of organisms to UVB radiation differs depending on its evolutionary position. During land plant evolution the radiation spectrum differed from current conditions, with higher UVB levels than at present, since the stratospheric ozone layer was still developing.Adaptations to UVB were needed to survive these harsh terrestrial conditions and this might have been an important factor in early land plant evolution. Since firstly UVB levels differed during land plant evolution and, secondly adaptations might be developed via different evolutionary lines, differences in UVB adaptations might be expected between plants which developed early versus later in the evolution of land plants.The European project UVAQTER[1] aimed to analyse, characterise and compare the functioning of UVB screens, i.e. compounds absorbing UVB radiation, in algae, charophycean algae, lichens, bryophytes to vascular plants, since these compounds were assumed to increase in complexity in accordance with the evolutionary line of vascular plants. The research presented in this thesis was part of UVAQTER. Given the importance of bryophytes and charophycean algae in the evolutionary line of land plant development, the overall aim of this thesis was to study the effects of UVB radiation on growth, DNA damage and induced UVB absorbing compounds in charophytes and bryophytes. In addition, the effects found in charophytes and bryophytes were placed in an ecological framework by analysing charophycean algae under both controlled and field conditions, and by including a comparison of the UVB effects in bry-