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The effects of UV-B radiation on photosynthesis and photosynthetic productivity of higher plants are reviewed. When plants were exposed to large UV-B doses in a glasshouse in order to study the mechanistic basis of UV-B-induced inhibition of photosynthesis, direct effects on stomata and on Calvin cycle enzymes (i.e. large decreases in ribulose-1,5-bisphosphate carboxylase/oxygenase and in sedoheptulose-1,7-bisphosphate) without any significant effect on photosystem II were observed. When plants were continuously grown and developed under UV-B in a glasshouse, exposure to UV-B only decreased adaxial stomatal conductance (g) of the leaves and consequently increased the stomatal limitation of CO uptake. Furthermore, field studies using realistic UV-B levels (i.e. a predicted 30% increase in this radiation) demonstrate a lack of UV-B effects on photosynthesis or on plant biomass. It is concluded that any predicted future increase in UV-B irradiation is unlikely to have a significant impact on the photosynthetic characteristics and productivity of higher plants.

Sunlight is the energy source for photosynthesis in all land plants and in many aquatic organisms. On the other hand, solar irradiation may also appear as a stress, specially when it is combined with other factors, such as deviations from optimal growth conditions (temperature, water status) or with environmental pollutants (heavy metals, air pollutants, acidic rain). The adaptation and acclimation of photosynthetic organisms to changing environmental conditions is important, not only for the plant’s survival but also for manking utilising them as food, raw material and energy source. Reactive oxygen species (ROS, also known as active oxygen species, AOS) are associated with stress and stress response in many ways: They may appear as primary elicitors, as propagators of oxidative damage, or as by-products. More recently, ROS are also considered as messenger molecules involved in signalling pathways, thus potential inducers of defence or adaptation. Until recently, the involvement of ROS in stress was usually presumed from products of oxidative damage. These techniques are useful and important, but - unlike more direct methods-they provide little information about the primary reactions. Also, due to increasing recognition of ROS in signal transduction - when they are present at low levels and do not cause much oxidative damage - methods for direct ROS detection are of special importance. After giving an overview on basic ROS chemistry, this chapter will illustrate direct and indirect methods of ROS detection with special emphasis on plants and their response to UV-B (280–320 nm) irradiation.

Aquatic ecosystems produce about 50% of the global biomass and play an important role in atmospheric carbon dioxide cycling. Since the primary producers are confined to the euphotic zone for energetic reasons, they are simultaneously exposed to short wavelength radiation. Solar UV affects growth, reproduction, photosynthetic production and many other physiological processes. Cyanobacteria are important ubiquitous prokaryotes which populate terrestrial and aquatic habitats. They account for up to 40 % of the marine biomass production and are important components of wet land ecosystems such as rice paddy fields. These organisms are also highly impaired by solar UV, but they and other motile microorganisms have developed mitigating strategies to protect themselves from this stress. One protection strategy is based on vertical migrations within the water column or a microbial mats. However, both motility and orientation are impaired by UV radiation. Another means of protection is achieved by the production of screening pigments including mycosporine-like amino acids (MAA) or scytonemins. MAAs are also produced by phytoplankton and macroalgae. In several organisms action spectra were measured which indicate that MAA synthesis is induced by UV in most cases. These sunscreen pigments prevent short wavelength radiation from reaching the UV sensitive DNA where it induces thymine dimers. Remaining dimers are removed by photorepair which involves the enzyme photolyase. The photosynthetic apparatus is another main target in primary aquatic biomass producers. Inhibition of the photosynthetic electron transport chain can be determined by oxygen measurements or by pulse amplitude modulated (PAM) fluorescence. Plants reduce the potentially deleterious effects of solar UV by decreasing the photosynthetic electron transport in photosystem II, a process called photoinhibition. Despite the dramatic effects of even ambient solar UV on individual species and physiological responses, the effect of ozone depletion on whole ecosystems is surprisingly low and close to the noise level induced by all other environmental factors such as mixing layer depth, cloud cover and temperature.

Aquatic ecosystems produce about 50% of the global biomass and play an important role in atmospheric carbon dioxide cycling. Since the primary producers are confined to the euphotic zone for energetic reasons, they are simultaneously exposed to short wavelength radiation. Solar UV affects growth, reproduction, photosynthetic production and many other physiological processes. Cyanobacteria are important ubiquitous prokaryotes which populate terrestrial and aquatic habitats. They account for up to 40 % of the marine biomass production and are important components of wet land ecosystems such as rice paddy fields. These organisms are also highly impaired by solar UV, but they and other motile microorganisms have developed mitigating strategies to protect themselves from this stress. One protection strategy is based on vertical migrations within the water column or a microbial mats. However, both motility and orientation are impaired by UV radiation. Another means of protection is achieved by the production of screening pigments including mycosporine-like amino acids (MAA) or scytonemins. MAAs are also produced by phytoplankton and macroalgae. In several organisms action spectra were measured which indicate that MAA synthesis is induced by UV in most cases. These sunscreen pigments prevent short wavelength radiation from reaching the UV sensitive DNA where it induces thymine dimers. Remaining dimers are removed by photorepair which involves the enzyme photolyase. The photosynthetic apparatus is another main target in primary aquatic biomass producers. Inhibition of the photosynthetic electron transport chain can be determined by oxygen measurements or by pulse amplitude modulated (PAM) fluorescence. Plants reduce the potentially deleterious effects of solar UV by decreasing the photosynthetic electron transport in photosystem II, a process called photoinhibition. Despite the dramatic effects of even ambient solar UV on individual species and physiological responses, the effect of ozone depletion on whole ecosystems is surprisingly low and close to the noise level induced by all other environmental factors such as mixing layer depth, cloud cover and temperature.

Ultraviolet radiation is a well known damaging factor of plant photosynthesis. Here we studied the mechanism of damage induced by the UV-B and UV-A spectral regions to the light energy converting Photosystem II (PSII) complex, which is the origin of electron flow for the whole photosynthetic process. Our results show that the primary UV damage occurs at the catalytic Mn cluster of water oxidation, which is most likely sensitized by the UV absorption of Mn(III) and Mn(IV) ions ligated by organic residues. The presence of visible light enhances the photodamage of PSII, but has no synergistic interaction with UV radiation. UV-induced damage of PSII can be repaired via synthesis of the D1 and D2 reaction center protein subunits. This process is facilitated by low intensity visible light, which thereby can protect against UV-induced damage. However, the photodamage induced by visible light at high intensity (above 1000 µEms) cancels the protective effect. The protein repair of PSII is also retarded by the lack of DNA repair as shown in a photolyase deficient cyanobacterial mutant.

Colored or chromophoric dissolved organic matter (CDOM) is by definition that portion of the dissolved organic matter (DOM) capable of absorbing light (i.e. contains chromophores). It represents a dominant absorbing species in natural waters and therefore it plays a critical role in controlling the light distribution in aquatic environments. CDOM shows a featureless absorption spectrum that increases exponentially with decreasing wavelength. Under light exposure CDOM loses its optical properties (photobleaching), altering the aquatic light field. Field and laboratory studies indicate that the CDOM photobleaching can represent a quite significant sink of this material over a short time scale.

Members of the cyanobacteria are cosmopolitan in distribution, forming a prominent component of microbial populations in aquatic as well as terrestrial ecosystems. They play a central role in successional processes, global photosynthetic biomass production and nutrient cycling. In addition, N-fixing cyanobacteria are often the dominant microflora in wetland soils, especially in rice paddy fields, where they significantly contribute to fertility as a natural biofertilizer. Recent studies have shown a continuous depletion of the stratospheric ozone layer, as a result of anthropogenically released atmospheric pollutants such as chlorofluorocarbons (CFCs) and the consequent increase in solar UV-B radiation reaching the Earth’s surface. Considering the vital role of cyanobacteria in crop production, the fluence rates of UV-B radiation impinging on the natural habitats are of major concern since, being photoautotrophic organisms, cyanobacteria depend on solar radiation as their primary source of energy. UV-B radiation causes reduction in growth, survival, protein content, heterocyst frequency and fixation of carbon and nitrogen, bleaching of pigments, disassembly of phycobilisomal complexes, DNA damage and alteration in membrane permeability in cyanobacteria. However, a number of cyanobacteria have developed photoprotective mechanisms to counteract the damaging effects of UV-B which includes synthesis of water soluble colourless mycosporine-like amino acids (MAA) and the lipid soluble yellow-brown coloured sheath pigment, scytonemin. Cyanobacteria, such as sp., sp. and sp. were isolated from rice paddy fields and other habitats in India and screened for the presence of photoprotective compounds. Spectroscopic and biochemical analyses revealed the presence of only shinorine, a bisubstituted MAA containing both a glycine and a serine group with an absorption maximum at 334 nm in all cyanobacteria except sp. There was a circadian induction in the synthesis of this compound by UV-B. A polychromatic action spectrum for the induction of MAAs in sp. and also shows the induction to be UV-B-dependent and peaking at around 290 nm. Another photoprotective compound, scytonemin, with an absorption maximum at 386 nm (which also absorbs significantly at 300, 278, 252 and 212 nm) was detected in all cyanobacteria except sp. In addition, two unidentified, water-soluble, yellowish (induced by high white light) and brownish (induced by UV-B) compounds with an absorption maximum at 315 nm were recorded only in sp. In conclusion, cyanobacteria having photoprotective mechanisms may be potent candidates as biofertilizers for crop plants.

This paper reviews some of the results described in the literature on the effect of UV-B radiation on ciliated protozoa, concentrating in particular on the changes induced in motility and photomotility, which are both important in determining the capability of these organisms to survive in their environment. It will be shortly described what ciliates are and why they are an important component of ecological systems. A summary will follow of the early works, where the effects of UV radiation on ciliates were investigated. Finally, it will be described in some more detail the results of studies on a marine ciliate, , and two fresh-water ciliates, and .

From the data stated above it appears that at least a combination of an activated oncogenic pathway and an inactivated tumor suppressor gene is needed in order for a skin cancer to arise: in SCC it is possibly an activated RTK/RAS pathway in combination with dysfunctional P53 tumor suppression, in BCC the Hedgehog pathway with possibly dysfunctional P53, and in CM again possibly an activated RTK/RAS in combination with inactivation of the INK4a locus. These combinations may be required, but not necessarily sufficient for the development of a tumor. Additional oncogenic events may be necessary.

Although the skin cancers appear to be related to UV radiation, the effect of UV radiation is only unambiguously clear in point mutations of in SCC and BCC. The mutations found in the other relevant genes are of a wider variety, which may (in part) be caused by solar UV radiation. Experiments are needed to clarify if and how UVB or UVA radiations can affect other relevant genes. Overall, the data presently weigh most heavily toward the carcinogenic effect of UVB radiation: the latest data on experimental induction of CM in the opossum are not indicative of any important contribution of UVA radiation next to the dominant carcinogenicity of UVB radiation

Ultraviolet radiation is a well known damaging factor of plant photosynthesis. Here we studied the mechanism of damage induced by the UV-B and UV-A spectral regions to the light energy converting Photosystem II (PSII) complex, which is the origin of electron flow for the whole photosynthetic process. Our results show that the primary UV damage occurs at the catalytic Mn cluster of water oxidation, which is most likely sensitized by the UV absorption of Mn(III) and Mn(IV) ions ligated by organic residues. The presence of visible light enhances the photodamage of PSII, but has no synergistic interaction with UV radiation. UV-induced damage of PSII can be repaired via synthesis of the D1 and D2 reaction center protein subunits. This process is facilitated by low intensity visible light, which thereby can protect against UV-induced damage. However, the photodamage induced by visible light at high intensity (above 1000 µEms) cancels the protective effect. The protein repair of PSII is also retarded by the lack of DNA repair as shown in a photolyase deficient cyanobacterial mutant.