Effects of increased UV-B radiation on the lichen Cladonia arbuscula spp. mitis: UV-absorbing pigments and DNA damage

Lichens, a form of symbiosis between a fungal and a photosynthetic partner, are believed to be a group that evolved early in the history of terrestrial life. As a consequence, they probably experienced higher ultraviolet (UV) radiation fluxes than at present. However, in the last two decades, due to the depletion of the stratospheric ozone layer, increasing levels of ultraviolet-B radiation (280-315 nm) are reaching the earth€ surface. In this thesis the effects of enhanced UV-B radiation were studied on the apical (€tips€) and central (€stems€) regions of the podetial thallus of the lichen Cladonia arbuscula ssp. mitis. Effects of UV-B radiation on lichen DNA were investigated by measuring the accumulation of cyclobutane pyrimidine dimers (CPDs) by means of the enzyme-linked immunosorbant assay technique (ELISA). ELISA was also used for assessing the capacity of lichens to repair DNA damage by measuring the decrease in CPD content. UV-absorbing pigment content and changes in penetration of light within the tissue were investigated by means of spectrophotometric measurements of lichen acetone-ethanolic extracts and fibre optic measurements of internal radiation gradients, respectively. After 7 days of exposure to high light (HL; 800 _mol m-2 s-1) with or without enhanced UV-B radiation (13 kJ m-2 day-1) UV-absorbing pigments and CPDs accumulated in both tips and stems of air-dry lichens. However, stems showed a larger increase in total phenolic content and lower CPD accumulation than tips. In an outdoor experiment, after three months exposure to natural sunlight, where the UV-B component had been removed or where supplemental UV-B radiation had been added (simulating 15% ozone depletion), the highest increases in pigment content were found in stems of those lichens grown under supplemental UV-B radiation. Fibre optic measurements showed a decreased light penetration (280 nm) within the thallus of lichens grown under enhanced UV-B radiation. Short-term exposure to UV-B radiation (7.4 kJ m-2 day-1) of hydrated lichen thalli kept at either 25oC or at 2oC resulted in the accumulation of CPDs. Subsequent exposure to photosynthetically active radiation (PAR, 300 _mol m-2 s-1, 400-700 nm) decreased the CPD content only in hydrated lichen thalli kept at 25oC, whereas there was no change in thalli kept at 2oC. Exposure to UV-B radiation in combination with PAR resulted in the absence of accumulation of CPDs in hydrated lichen thalli kept at 25 oC, whereas in hydrated thalli kept at 2oC CPD levels were as high as after exposure to UV-B only. Throughout all experiments stems showed consistently lower levels of CPDs and a higher degree of repair than tips. Monitoring of photolyase repairing activity also showed that a higher percentage of pyrimidine dimers was repaired in stems than in tips. From the results it was evident that water content and temperature represent two important factors in the response of Cladonia arbuscula ssp. mitis to UV-B radiation, since air-dry thalli were more susceptible to UV-induced DNA damage and less capable of repairing CPDs than hydrated thalli. Further, hydrated thalli kept at low temperatures were not able to repair the accumulated DNA damage. An apparent protective mechanism against UV radiation in air-dry lichens was the accumulation of UV-absorbing pigments, which consequently reduced the penetration of light within the thallus. Tips have shown to be those thallus parts most susceptible to damage caused by UV-B radiation as they accumulated the highest amounts of DNA damage, exhibited the least repair capacity and the lowest relative increase in phenolic pigment content

Hydrogen and Carbon Nanotubes from Pyrolysis-Catalysis of Waste Plastics: A Review

More than 27 million tonnes of waste plastics are generated in Europe each year representing a considerable potential resource. There has been extensive research into the production of liquid fuels and aromatic chemicals from pyrolysis-catalysis of waste plastics. However, there is less work on the production of hydrogen from waste plastics via pyrolysis coupled with catalytic steam reforming. In this paper, the different reactor designs used for hydrogen production from waste plastics are considered and the influence of different catalysts and process parameters on the yield of hydrogen from different types of waste plastics are reviewed. Waste plastics have also been investigated as a source of hydrocarbons for the generation of carbon nanotubes via the chemical vapour deposition route. The influences on the yield and quality of carbon nanotubes derived from waste plastics are reviewed in relation to the reactor designs used for production, catalyst type used for carbon nanotube growth and the influence of operational parameters

UV-induced changes in pigment content and light penetration in the fruticose lichen Cladonia arbuscula ssp. mitis

The response of the lichen, Cladonia arbuscula (Wallr.) Flot. ssp. mitis (Sandst.) Ruoss to enhanced UV-B (280-315 nm) radiation was investigated with respect to: (a) changes in phenolic content; (b) differential pigment accumulation under visible and UV radiation with increasing distance from thallus apices; and (c) the internal distribution of UV-B radiation within the thallus measured with quartz optical fibres. In a short-term experiment, lichens were exposed for 7 days in a growth chamber to visible light with or without additional UV-B radiation. For a longer term experiment, lichens were grown outdoors under both natural UV radiation, and supplemental UV-A (315–400 nm)+UV-B provided by lamps. Controls were placed under filters that removed the radiation below 290 nm from the natural sunlight. The concentration of total phenolic compounds was measured spectrophotometrically at the termination of the experiments, in different parts of the lichen podetia. UV-exposed lichens showed increased accumulation of phenolics compared to those not grown under UV. At the termination of the long-term experiment, fibre optic measurements of the penetration of radiation into lichen thallus reflected the influence of growth under UV radiation, whereby UV was more strongly attenuated as compared to that in lichens not exposed to enhanced levels of UV-B radiation. Results indicated that in Cladonia, UV-B radiation induces the accumulation of phenolic compounds that may have a protective role. In addition, the morphological distribution of phenolic compounds was different under visible and supplemental UV-B radiation. Internal radiation measurements served to visualise the attenuation of radiation with thallus depth for different wavelengths in the UV-B waveband

The chloroplast small heat shock protein undergoes oxidation-dependent conformational changes and may protect plants from oxidative stress

The nuclear-encoded chloroplast-localized Hsp21 is an oligomeric heat shock protein (Hsp), belonging to the protein family of small Hsps and @a-crystallins. We have investigated the effects of high temperature and oxidation treatments on the structural properties of Hsp21, both in purified recombinant form and in transgenicArabidopsis thalianaplants engineered to constitutively overexpress Hsp21. A conformational change was observed for the 300 kDa oligomeric Hsp21 protein during moderate heat stress (=<40oC) ofArabidopsisplants, as judged by a shift to lower mobility in non-denaturing electrophoresis. Similar changes in mobility were observed when purified recombinant Hsp21 protein was subjected to an oxidant. Exposure of Hsp21 protein to temperatures above 70oC led to irreversible aggregation, which was prevented in presence of the reductant dithiothreitol. The transgenic plants that constitutively overexpressed Hsp21 were more resistant to heat stress than were wildtype plants when the heat stress was imposed under high light conditions. These results suggest that the physiological role of Hsp21 involves a response to temperature-dependent oxidative stress

Water- and temperature-dependence of DNA damage and repair in the fruticose lichen Cladonia arbuscula ssp mitis exposed to UV-B radiation

The induction of cyclobutane pyrimidine dimers (CPDs) by ultraviolet-B radiation (UV-B, 280-315 nm) and repair mechanisms were studied in the lichen Cladonia arbuscula ssp. mitis exposed to different temperatures and water status conditions. In addition, the development and repair of CPDs were studied in relation to the different developmental stages of the lichen thallus podetial branches. Air-dried lichen thalli exposed to UV-B radiation combined with relatively high visible light (HL, 800 mumol m(-2) s(-1); 400-700 nm) for 7 days showed a progressive increase of CPDs with no substantial repair, although HL was present during and after irradiation with UV-B. Fully hydrated lichen thalli, that had not been previously exposed to UV-B radiation for 7 days, were given short-term UV-B radiation treatment at 25degreesC, and accumulated DNA lesions in the form of CPDs, with repair occurring when they were exposed to photoreactivating conditions (2 h of 300 mumol m(-2)s(-1), 400-700 nm). A different pattern was observed when fully hydrated thalli were exposed to short-term UV-B radiation at 2degreesC, in comparison with exposure at 25degreesC. High levels of CPDs were induced at 2degreesC under UV-B irradiation, without significant repair under subsequent photoreactivating light. Likewise, when PAR (300 mumol m(-2)s(-1) ) and UV-B radiation were given simultaneously, the CPD levels were not lowered. Throughout all experiments the youngest, less differentiated parts of the lichen thallus - namely 'tips', according to our arbitrary subdivision - were the parts showing the highest levels of CPD accumulation and the lowest levels of repair in comparison with the older thallus tissue ('stems'). Thus the experiments showed that Cladonia arbuscula ssp. mitis is sensitive to UV-B irradiation in the air-dried state and is not able to completely repair the damage caused by the radiation. Furthermore, temperature plays a role in the DNA damage repairing capacity of this lichen, since even when fully hydrated, C. arbuscula ssp. mitis did not repair DNA damage at the low temperatures

Accumulation of DNA damage in Antarctic mosses: correlations with ultraviolet-B radiation, temperature and turf water content vary amongst species

The susceptibility of three East Antarctic moss species to UV-B radiation was examined by measuring accumulation of cyclobutane pyrimidine dimers under natural sunlight during the austral summer season of 2002/03. The 2002/03 season was characterised by unusually low springtime ozone depletion and as such our results likely underestimate the DNA damage possible in a more typical UV-B radiation season. Despite this all three species accumulated significant DNA photoproducts. We also found a positive association between photoproduct accumulation and incident UV-B radiation in the two cosmopolitan species, Bryum pseudotriquetrum and Ceratodon purpureus, with more DNA damage in samples collected early in the season compared to later in the summer. For B. pseudotriquetrum negative associations were also observed between photoproduct accumulation and both turf water content and the 10 day mean air temperature. Photoproduct accumulation in the endemic species Schistidium antarctici was similarly high across the season and no significant association with environmental variables was found. Our results are consistent with the two cosmopolitan species having somewhat higher UV-B screening capabilities and possibly more efficient mechanisms for repairing DNA damage than the endemic S. antarctic