A higher mutation rate will eventually result in reduced gene expression and hence debilitation or even increased mortality

of algal cells. UV-B induced damage to proteins is mediated by aromatic amino acids or by disulfide bonds between cysteine residues, which can be easily cleaved VRT752271 ic50 after absorption of this waveband (Vass 1997). Typical target proteins in algae are those involved in photosynthesis, such as the D1 protein of photosystem II (PSII) and the enzyme Rubisco in the Calvin cycle (Campbell et al. 1998; Bischof et al. 2000); damage to these results in decreased photosynthetic activity and growth. However, since proteins typically occur as numerous copies inside the algal cell, any UV-induced damage to proteins is not as severe as the damage to DNA (Harm 1980). UV-B-induced photo-oxidative stress stimulates various cellular processes,

leading to the production of reactive oxygen species (ROS) such as superoxide radicals and hydrogen peroxide, as well as singlet-oxygen and hydroxyl radicals. The sources and production sites of ROS are mainly related to photosynthetic activities such as pseudocyclic photophosphorylation and the Mehler reaction, which stimulate the accumulation of hydrogen peroxide YH25448 cost (Asada 1994; Elstner 1990). UV-induced ROS are extremely toxic to algal cells, by causing oxidative damage to all biomolecules, particularly lipids. After a first initiation reaction, an unsaturated fatty acid is converted to a peroxyl radical, which in turn attacks another unsaturated fatty acid, finally leading to some kinds of free-radical cascades. This photochemical peroxidation of unsaturated fatty acids may be particularly damaging to membrane structure and function (Bischof et al. 2006). As a consequence of UV-induced damage to biomolecules,

many physiological processes are potentially impaired. Photosynthesis is probably the most intensively studied process Tyrosine-protein kinase BLK in plant sciences. Due to its biochemical complexity, numerous sites can be affected by UV-B. These can include inhibition of energy transfer within the PSII reaction center, the water-splitting complex, or the light-harvesting complex. Key enzymes such as Rubisco and ATPase are also typical targets. The common consequences of UV-B for photosynthetic function are decreased or even fully inhibited CO2-fixation, and hence a decline in primary production (Franklin and Forster 1997; Bischof et al. 2006). Nevertheless, the extent to which alpine BSC algae are affected by UVR is not well understood. The filamentous green alga Klebsormidium fluitans, strain ASIB V103, was isolated from a BSC underneath a stand of the grass Festuca rubra at 2,363 m a.s.l. (Pitschberg, St. Ulrich in Gröden, South Tyrol, Italy). In the laboratory, K.