Minisymposium 20: Global Change
Abs #
34001: Repair of DNA photoproducts in Antarctic mosses
The Antarctic continent is the coldest, highest, driest, windiest and most isolated landmass on earth. Growth conditions are therefore extreme, and plants exist at the physiological limits of survival. Antarctic plants are confined to the few ice-free areas and are exposed to a highly seasonal, rapidly variable and often extreme climate with frequent sub zero temperatures, an intermittent water supply and almost continuous sunlight in summer. In recent decades, these plants have also been exposed to increased levels of UV-B radiation, as a result of springtime ozone depletion. The annual occurrence of the ozone hole coincides with the time of emergence from winter dormancy beneath the protective snow cover, exposing plants to sudden elevations of UV-B radiation in combination with increased PAR and greater temperature fluctuations. Bryophytes, the dominant plants on continental Antarctica may be particularly susceptible to UV-B damage because of their simple structure, with most having leaves which are only one cell thick and lacking protective cuticles or epidermal layers. However, some Antarctic mosses have been shown to produce pigments that could act as protective screens against UV-B radiation.
If photoprotective strategies are insufficient, UV-B radiation is able to permeate plant tissues, damaging DNA and other macromolecules. 2 major photoproducts may be formed upon damage to DNA: cyclobutane-type pyrimidine dimers and pyrimidine (6,4) pyrimidones. Such DNA photoproducts prevent replication and gene transcription and thus have the potential to be mutagenic and disrupt cellular metabolism. Both forms of damage can be repaired in higher plants by either light-dependent (photorepair) reactions, catalysed by photolyases, or by excision repair which is light independent.
The accumulation of these photoproducts was determined in two Antarctic mosses, Ceratodon purpureus and Bryum pseudotriquetrum in response to high UV-B radiation. The repair of these DNA lesions was then investigated under a range of temperatures and under light and dark conditions. Monoclonal antibodies were used in an enzyme-linked immunosorbent assay to detect the formation of DNA damage products. Unlike many higher plants, significant repair of DNA photoproducts was observed in the dark, suggesting that photorepair maybe less important in these plants. These results will be discussed in relation to the capacity of Antarctic plants to withstand increased levels of UV-B radiation.
