Antarctic terrestrial ecosystem and role of pigments in enhanced UV-B radiations

摘要

The terrestrial ecosystem of Antarctica are among the most extreme on earth, challenging the communities and making their existence difficult by rapidly increasing annual summer influx of solar ultraviolet radiations (UV-R), extremely cold conditions and lesser availability of nutrients. Spring time ozone depletion is due to release of chlorofluorocar-bons in the earth atmosphere and is a serious cause of concern among environmentalists. Antarctic continent is mostly dominated by cryptogamic plants with limited distribution in different parts of the icy continent however; their distribution is mostly confined to Sub-Antarctic region. By the virtue of light requirement, cryptogams are exposed to extreme seasonal fluctuation in photosynthetically active radiation (PAR), and ultraviolet (UV) radiation which are closely associated with photosynthetic pigments in photoautotrophic organisms. Antarctic cryptogams cope up the stress imposed by UV radiation by the development of efficient systems for repairing damage by synthesis of screening compounds such as UV-B absorbing pigments and anthocyanin compounds. A major part of the UV absorbing compounds are appeared to be constitutive in lichens which are usnic acid, perlatolic acid and fumarphot-ocetraric acid which is particularly induced by UV-B. Secondary metabolites such as phenolics, atranorin, parietin and melanin also enhance the plant defense, by different molecular targets in specific solar irradiance and potential for increased antioxidative protection to UV induced vulnerability.