Desiccation protects Antarctic mosses from ultraviolet-B induced DNA damage

Antarctic mosses live in a frozen desert, and are characterised by the ability to survive desiccation. They can tolerate multiple desiccation-rehydration events over the summer growing season. As a result of recent ozone depletion, such mosses may also be exposed to ultraviolet-B radiation while desiccated. The ultraviolet-B susceptibility of Antarctic moss species was examined in a laboratory experiment that tested whether desiccated or hydrated mosses accumulated more DNA damage under enhanced ultraviolet-B radiation. Accumulation of cyclobutane pyrimidine dimers and pyrimidine (64) pyrimidone dimers was measured in moss samples collected from the field and then exposed to ultraviolet-B radiation in either a desiccated or hydrated state. Two cosmopolitan species, Ceratodon purpureus (Hedw.) Brid. and Bryum pseudotriquetrum (Hedw.) Gaertn., B.Mey. and Scherb, were protected from DNA damage when desiccated, with accumulation of cyclobutane pyrimidine dimers reduced by at least 60% relative to hydrated moss. The endemic Schistidium antarctici (Cardot) L.I. Savicz and Smirnova accumulated more DNA damage than the other species and desiccation was not protective in this species. The cosmopolitan species remarkable ability to tolerate high ultraviolet-B exposure, especially in the desiccated state, suggests they may be better able to tolerate continued elevated ultraviolet-B radiation than the endemic species.