| Summary: | Master of Science in Biological sciences. Depletion of the stratospheric ozone has allowed more solar ultraviolet (UV) radiation (100-400 nm) to reach the lower atmosphere. Despite the success of the continued implementation of Montreal protocol of 1987 and its amendments aimed at the protection of the ozone layer, it is possible that UV will remain elevated in some regions due to decreasing removal by clouds and aerosols. Strong interactions between ozone depletion and changes in climate induced by increasing greenhouse gases could result in increased UV radiation levels reaching the surface. Increased exposure to UV-B can cause significant damage to organisms including protein damage, inhibition of photosynthesis, formation of high energy reactive oxygen species (ROS), disruption of nitrogen fixation and induction of cell mutation and inhibition of growth. Lichens are composite organisms that arise from a symbiotic association between fungi and photoautotrophic algal partners, which may be microalgae and/or cyanobacteria. They have developed several protective strategies to protect themselves from excessive radiation. Lichens such as Cladonia rangiferina, Lobaria pulmonaria and Umbilicaria rossica are known to synthesize melanins in response to elevated levels of UV-B radiation. Synthesis of melanins is generally catalysed by enzymes that are involved in phenol coupling including P450 monooxygenases, ascorbate oxidases, peroxidases, laccases and tyrosinases (Nezbedová et al. 2001). The work presented in this thesis investigated the enzymes involved in melanin biosynthesis in lichens from suborder Peltigerineae. We present a detailed characterization of redox enzymes from Lobaria pulmonaria and Pseudocyphellaria aurata with a special focus on tyrosinases. Furthermore, an evaluation of the response of L. pulmonaria to UV radiation was done. The role of the redox enzymes tyrosinases, laccases and peroxidases in melanin synthesis is elucidated by exposing L. pulmonaria thalli to various combinations of UV and ...
|
|---|