Summary
Ozone depletion has resulted in large increases in springtime ultraviolet-B radiation (UV) over Antarctic plants since the 1970s. Studies of UV induced DNA damage in three Antarctic moss species have shown Ceratodon purpureus to be the most UV-tolerant, despite possessing less soluble UV-screening compounds than the co-occurring Bryum pseudotriquetrum. We used alkali extraction of cell wall-bound phenolics in combination with MeOH extraction of soluble phenolics to determine whether cell wall-bound UV-screens could explain the greater UV tolerance of C. purpureus. Spectrophotometric studies showed that B. pseudotriquetrum and C. purpureus had equal concentrations of UV-screening compounds overall but these were differentially distributed throughout the cell. Bryum pseudotriquetrum had equal concentrations of soluble and cell wall-bound UV-screens, whereas almost 80% of these compounds were associated with the cell wall in C. purpureus. In contrast, the Antarctic endemic Schistidium antarctici only possesses half the total UV-screens of the other species. Confocal microscopy confirmed the localisation of UV-screens in the three mosses and identification of these compounds by HPLC and LC-MS is ongoing. The greater investment in cell wall-bound compounds offers C. purpureus a more spatially uniform and potentially more effective UV screen, consistent with its cosmopolitan distribution and occurrence in many high UV environments. Our results confirm that S. antarctici has the least UV-screening potential, consistent with the hypothesis that this species may be disadvantaged under continuing springtime ozone depletion. Cell wall compounds are not usually determined in bryophytes but this research suggests they may be an important component of the UV defences of lower plants.