2004, Gruber, Ansgar

Effects of ultraviolet radiation on the formation and the germination of zoospores have been investigated in Laminaria digitata. Excised phylloid discs were exposed to controlled ultraviolet radiation of different qualities and intensities in the laboratory. Both sides of the discs were irradiated alternately. Rate of sorus formation, sorus area, zoospore release, amount of cyclobutane-pyrimidine dimers in DNA and germination rate of the released zoospores were determined. In order to determine the relevance of ultraviolet radiation for L.digitata, field measurements of irradiance were collected. The absorption characteristics of zoospore suspensions of the three Helgoland species of Laminaria were investigated. The investigations showed that for phylloid discs irradiated on both sides, ultraviolet radiation has no effect on sorus formation and sorus area. The germination rate of the zoospores was not negatively influenced by ultraviolet radiation during the formation of the sorus. This suggests an effective protection of the sporogenic tissue from ultraviolet radiation. DNA damage was shown in UVB irradiated phylloid discs. The DNA damage was higher in the non-fertile regions of the phylloid discs than in the sorus tissue. Therefore, additional UVB protection mechanisms are suspected. In the field, UVB intensities capable of damaging zoospores were found. In L. digitata, both the zoospores and exudates contribute to the UV absorption of zoospore suspensions. The proportion of the total absorption caused by exudates is higher in L. saccharina and L. hyperborea. In these species, the zoospores themselves show hardly any absorption. Possibly, a significant proportion of exudation takes place in the sorus tissue. All results indicate that L. digitata has adaptive answers to ultraviolet radiation, which counteract the detrimental effects of ultraviolet radiation. This diploma thesis was carried out at the Biologische Anstalt Helgoland. 1. Referee (Advisor): Professor Dr. P. Kroth, University of Konstanz; 2. Referee: Professor Dr. C. Wiencke, Alfred Wegener Institute for Polar and Marine Research, Bremerhaven.