Leaf epidermal transmittance of ultraviolet radiation and its implications for plant sensitivity to ulraviolet-radiation induced injury

Summary Leaf epidermal transmittance of ultraviolet radiation (280–400 nm) was examined in several plant species to determine the capability of the epidermis to attenuate solar ultraviolet radiation. Epidermal samples were mechanically isolated and examined with a spectroradiometer/integrating sphere for transmittance. A survey of 25 species exposed to natural insolation was conducted. Although the species differed in life form, habitat type, and epidermal characteristics, epidermal transmittance was generally less than 10%. Ultraviolet radiation was attenuated 95 to 99% in more than half of the species. In 16 species, flavonoid and related pigments in the epidermis accounted for 20 to 57% of the attenuation. Several species exposed to supplemental ultraviolet irradiation (288–315 nm) in a greenhouse exhibited significant (P0.05) depressions in epidermal transmittance of 31 to 47%, apparently resulting from an increase in ultraviolet-absorbing pigments.     

Effects of UV-B Radiation on Anti-predator Behavior in Three Species of Amphibians

Ultraviolet radiation has been suggested as a possible contributing cause of amphibian declines around the world. Both laboratory and field studies have demonstrated that exposure to ultraviolet radiation can lead to increased mortality of developing amphibians. Virtually no studies have examined the sub‐lethal effects of ultraviolet on amphibian behavior. In this study, we examine the anti‐predator behavior of three species of amphibians after short‐term exposure to ultraviolet‐B radiation. Toad (Bufo boreas) juveniles that had been exposed to ultraviolet radiation did not respond to chemical extracts from conspecifics and heterospecifics as much as juveniles that had not been exposed. Both newt larvae (Taricha granulosa) that had been exposed to ultraviolet radiation and those that had not been exposed responded to chemical cues from conspecific predators by increasing the amount of time spent in shelter. Frog tadpoles (Rana cascadae) that had been exposed to ultraviolet radiation did not reduce their movement in response to chemical cues from predators as much as tadpoles that had not been exposed. These results indicate that ultraviolet exposure may have important sub‐lethal effects in amphibians that could adversely effect their fitness.     

紫外辐射的细胞生物学效应及其机制

地球表面的生物体会受到来自阳光紫外辐射的照射。两极臭氧层空洞的形成使地球表面的紫外辐射水平,特别是UVB的水平增加,进而对生物体的危害日益加重。因此,深入研究紫外辐射生物学效应的信号转导机制并阐明其损伤机制和生物体的反应机制等具有重要意义,也可为紫外辐射损伤防护的研究提供新思路。本文综述了本领域近年来的相关研究,从紫外辐射所致生物学效应的信号转导机制(包括对DNA的直接损伤作用、细胞膜激酶和非激酶受体通路、细胞质通路以及microRNA)等方面对紫外辐射的损伤机制进行了比较系统的阐述和总结。     

Resistivity of Spores to Ultraviolet and γ Radiation while Exposed to Ultrahigh Vacuum or at Atmospheric Pressure

Viability studies were conducted on microbial spores subjected to ultrahigh vacuum (UHV) in the 10(-9) to 10(-10) torr range. After 5 to 7 days in vacuum, they were exposed to ultraviolet (UV) or to gamma radiation either while still under vacuum or in the presence of dried air. Among the four test organisms subjected to UHV and ultraviolet radiation, Aspergillus niger was the most resistant; Bacillus megaterium, B. subtilis var. niger, and B. stearothermophilus were about equally less resistant. All four spores were more sensitive to ultraviolet radiation when UHV-dried than when desiccant-dried. Of the four test organisms subjected to UHV and gamma radiation, B. megaterium proved to be the most resistant; A. niger was the least resistant; and the remaining two organisms were of intermediate resistivity. All four organisms were less radiation resistant when UHV-dried than when irradiated in their normally hydrated state, and all showed an increased radiosensitivity after vacuum drying when oxygen was present. In addition, spores of B. subtilis var. niger and A. niger were less radiosensitive when UHV-dried and irradiated in vacuum than when "wet" and irradiated in air, whereas the reverse relationship was observed for the remaining two organisms. Based on the fact that microbial contaminants can be readily shielded from UV light by soils, metal particles, etc., and considering that the levels of ionizing radiations reported to be present in interstellar space are generally lower than those used in these experiments, the decrease in radioresistivity imparted by UHV drying is not of a sufficient magnitude to sterilize dependably portions of a spacecraft while on a mission.     

The effect of pulse UV plasma irradiation of liquid through rat skin

The formation of active particles in water samples exposed to ultraviolet radiation from spark discharge plasma in an atmosphere of air was investigated. The surface of the water samples was either exposed or covered by rat skin. The products accumulated in water during the first 3 days were identified as nitrite ions NO ₂ ^? , and the final product was identified as NO ₃ ^? . The intermediate products that occurred on the 3rd day and disappeared on the 14th day after the treatment were identified as peroxynitrous acid and peroxynitrite. The formation of these compounds can be associated with the decay of a long-lived complex formed under the influence of pulsed ultraviolet radiation. The decrease in pH observed in all samples could be due to the isomerization of peroxynitrous acid (ONOOH → HNO₃) that diffused through the skin as a component of a long-lived complex.     

The interaction of UVA and UVB wavebands with particular emphasis on signalling

The molecular response mechanisms and signalling pathways activated upon exposure to ultraviolet (UV) radiation have been extensively studied within the last two decades. Although many signalling pathways can be activated by both UVA as well as UVB, there are several distinctions indicating wavelength-specific response patterns accommodated by the terms UVA response and UVB response. Given that human skin is primarily exposed to UV light from solar radiation consisting of both UVA and UVB, we sought to explore a potential interaction between the distinct UVA and UVB responses at the level of MAPK. Our results indicate that the two distinct stress responses elicited by UVA or UVB interact with each other, producing a "third" response that is different from either alone and cannot be explained by a simple addition of effects.     

Formation of fatty acid esterified vitamin D3 in rat skin by exposure to ultraviolet radiation

The formation of fatty acid esters of vitamin D3 was demonstrated in rat skin exposed to artificial ultraviolet rays by using multi-dimensional high-performance liquid chromatography, ultraviolet spectrophotometry, and gas-liquid chromatography-mass spectrometry. This result indicated that the fatty acid esters of 7-dehydrocholesterol in rat skin (at least 80% of 7-dehydrocholesterol in rat skin is esterified) is also isomerized into vitamin D3 ester in vivo. The initial percentage of the esterified form was 84.3% and this did not significantly change up to the time when about half of the skin total vitamin D3 disappeared (2 days). Consequently, it was speculated that the vitamin D3 ester was delivered into the blood circulation from skin without having been hydrolyzed. This was supported by the presence of vitamin D3 ester in rat plasma exposed to ultraviolet radiation. In addition, in connection with the study of the restriction of vitamin D3 synthesis, distribution of total vitamin D3 in rat skin exposed to ultraviolet irradiation in vivo was compared with that in isolated skin exposed to ultraviolet radiation. The dermal layer of the isolated skin contained about 4 times more total vitamin D3 than that of in vivo skin. This finding suggests not only that ultraviolet rays could not penetrate deeply into the in vivo skin, but that the restriction of cutaneous synthesis of vitamin D3 observed in vivo may arise from this reduced penetration of ultraviolet rays.     

Melanocytes: morphological basis for an exteroceptive sensory system for monitoring ultraviolet radiation

From the conventional medical perspective, melanocytes have been traditionally viewed as epidermal responders/reactors to ultraviolet radiation. In this paper we have begun an analysis of the functional significance of melanocytes as monitors for ultraviolet radiation with their neuronal, endocrinological and immunological intercalations. This preliminary study was performed using as a human model unilateral sural nerve sensory blockade before and after ultraviolet exposure to both feet while the unblocked foot acted as the control. Full thickness surgical skin biopsies were taken of (I), normal pre-exposure skin, in the center of the two centimeter exposure area of both the sural nerve blocked area (II-III) and control (IV-V) one centimeter outside the exposed area in both the sural nerve blocked foot and the control or non-blocked foot. The objective clinical, blinded morphological and immuno-histochemical data from this experiment support the initial conclusion that neuronal connection is necessary for the normal ultraviolet exposure dermal reaction. Based upon this study, we further propose the existence of an exteroceptive sensory system in which melanocytes, with direct nervous system connection initiate an ultraviolet radiation reactive response that mobilizes both conventional endocrine and immune pathways.     

Effects of ultraviolet radiation on the tension and the cyclic GMP level of bovine mesenteric arteries

Strips of bovine mesenteric arteries brought to sustained contraction by the addition of 3.0 microM phenylephrine relaxed when exposed to ultraviolet radiation (366 nm). The relaxation was reversible and associated with a rapid increase in the cGMP content. After termination of the radiation the cGMP level rapidly decreased below the basal level. The crude soluble guanylate cyclase from the artery was stimulated about 8-fold by ultraviolet radiation (366 nm). Neither the cGMP-phosphodiesterase activity nor the cAMP level were found to be changed during irradiation. The ultraviolet light-induced relaxation was not dependent on an intact intimal surface. Furthermore, the relaxing effect was found to be enhanced and accompanied by a larger increase of the cGMP level in nitroglycerin-tolerant arteries. The present results show that the ultraviolet light-induced relaxation in bovine mesenteric arteries is associated with a rapid increase in the cGMP content and that ultraviolet light and nitrocompounds may exert their relaxing actions through a common substance.     

Effects of solar radiation on bacterial and fungal density on aquatic plant detritus

1. The effects of solar radiation on bacterial and fungal growth on aquatic macrophyte detritus were studied in a microcosm experiment. Senescent leaves of Phragmites australis were incubated for 63 days in shallow water in the shade under photosynthetically active radiation (PAR) together with ultraviolet radiation, or under filters removing either ultraviolet B (UVB) or both UVB and ultraviolet A (UVA). 2. Bacterial abundance and bacterial ³H-leucine incorporation in the water were measured, together with α- and β-D-glucosidase activity. In addition, bacterial abundance and fungal biomass associated with the litter were measured. 3. The results indicate that both PAR and UVA affect the micro-organisms involved in the decomposition of leaf litter. The α/β-D-glucosidase activity ratio was less than one in irradiated and more than one in shaded microcosms, suggesting a change in the substrate dissolved organic matter composition towards more β- than α-glycosidic linkages as a result of solar radiation. 4. Microcosms receiving UVB displayed a significantly higher β-D-glucosidase activity than shaded microcosms, and those exposed to PAR or PAR + UVA, demonstrating the potential importance of UVB radiation. 5. The free-living bacteria tended to be dominated by filamentous forms in microcosms subject to solar radiation, especially PAR, and attached microbial communities showed a greater tendency to be dominated by bacteria in irradiated microcosms than in shaded microcosms.     

Ultraviolet Radiation Absorbance by Coral Reef Fish Mucus: photo-protection and Visual Communication

Tropical reef fishes are exposed to high levels of damaging ultraviolet radiation. Here we report the widespread distribution of both UVA- and UVB-absorbing compounds in the epithelial mucus of these fishes. Mucus from 137 reef fish species was examined by spectrophotometry and 90% were found to have strong absorbance peaks between 290 and 400nm. Most fish species (78%) had more than one peak, that suggests a broad-band ultraviolet screening function for their mucus. Thalassoma duperrey, a tropical wrasse, was able to alter the absorbance of its epithelial mucus in response to both naturally and experimentally manipulated UV regimes. Visual modeling suggests that a fish with UV vision, such as Dascyllus albisella, could detect the changes in mucus spectra of T. duperrey that occurred in these experiments.     

Mycochrome system and the effect of molecular oxygen in the reversible photoinduction of conidiation in the fungus, Alternaria cichorii

Coniditation the fungus, Alternaria cichorii Nattras (IMI 225641), was repeatedly induced and inhibited by alternating doses of near ultraviolet and blue radiation. The final response largely depended on the last kind of radiation administered. When the final radiation was near ultraviolet, conidiophore formation was induced, and conidia were then produced in the subsequent dark period; when it was blue, the induction of conidiation was suppressed. The inductive effect of near ultraviolet was promoted by anaerobiosis, but the reversing effect by blue radiation was not influenced by molecular oxygen. Thus, the "mycochrome" system apprears to control induction of conidiation in Alternaria cichorii , and oxidation-reduction processes may be involved in its function.     

光活化杀虫剂α-三噻吩的电子自旋共振分析及其对库蚊保护酶系统活性的影响

以淡色库蚊Culex pipiens pallens为试材,初步进行了典型光活化杀虫剂α-三噻吩（α-T）的电子自旋共振（ESR）分析,并研究其对昆虫保护酶系统的影响。ESR分析表明,近紫外光和药剂α-T均可促进活性氧自由基浓度升高,且两者具有协同关系,近紫外光能显著促进α-T增加自由基的作用,处理3 h时试虫自由基总浓度增加了99.6%。近紫外光和药剂α-T对保护酶系统的影响随酶的种类而有所不同,但在近紫外光存在的条件下,α-T对超氧物歧化酶（SOD）、过氧化物酶（POD）和过氧化氢酶（CAT）活体活性均有抑制作用,且光照3 h时,抑制作用最强。     

Ultraviolet-B Radiation-induced Inhibition of Leaf Expansion and Promotion of Anthocyanin Production: Lack of Involvement of the Low Irradiance Phytochrome System

Leaf discs from expanding leaves of Rumex patientia L. were exposed to 7 hours of visible plus different levels of ultraviolet radiation in the 290 to 315 nm waveband (UV-B) and then placed in darkness. Leaf disc expansion was reduced and anthocyanin production was increased in discs exposed to moderate or high levels of UV-B radiation when compared to control discs. The possibility that the inhibition of leaf expansion by UV-B radiation might be at least partially phytochrome-mediated was examined by giving discs brief red or far red irradiation following exposure to UV-B radiation. Brief red radiation (R) following treatment with moderate or high UV-B radiation did not alter the pattern of growth or anthocyanin production compared to discs placed in darkness following UV-B treatment. However, a posttreatment with far red radiation (FR) reduced the growth of discs subjected previously to either moderate UV-B or no UV-B irradiation to the level of growth of discs given high UV-B. FR posttreatment also decreased anthocyanin production in discs in moderate and high UV-B treatments. Effects of FR and UV-B radiation apparently do not involve the same mechanism. This was demonstrated by experiments in which FR following the UV-B treatments was in turn followed by R, which reversed the effects of the FR but did not alter the growth inhibition or increased anthocyanin production induced by moderate or high levels of UV-B radiation.     

Ecological modulation of environmental stress: interactions between ultraviolet radiation, epibiotic snail embryos, plants and herbivores

1. The distribution of egg masses of the freshwater snails Lymnaea stagnalis and Planorbarius corneus on the undersides of water lily leaves (e.g. Nuphar lutea) is related to the prevalence of the leaf-mining beetle Galerucella nymphaeae. 2. When given the choice, Planorbarius significantly avoids leaves that were infested by the mining beetle. Conversely, Lymnaea did not discriminate against mined leaves. 3. Intact Nuphar leaves block over 95% of incident ultraviolet radiation. Yet, ultraviolet transmission reaches almost 100% under beetle mining scars. These are several times wider than snail embryos. 4. When exposed to natural sunlight, Lymnaea embryos proved to be resistant to ambient ultraviolet, while Planorbarius embryos were rapidly killed. Thus, one selective advantage of Planorbarius discrimination against mined leaves when depositing its eggs could be the avoidance of ultraviolet radiation passing through mining scars. 5. Other mining-related modifications of the leaves, reduced area, decreased longevity, altered aufwuchs (i.e. biofilm and epibionts) are discussed but seem less relevant for the oviposition preference of Planorbarius. 6. The discriminatory behaviour of this snail species was triggered by water-borne cues emitted by the damaged leaf, not by the eggs or larvae of the beetle. 7. This study illustrates how environmental stress on a given species, ultraviolet radiation in this case, can be ecologically buffered (shading by Nuphar) or enhanced (reduction of Nuphar shading through beetle mining) by associated species. It highlights how the impact of a given stress depends on the identity of the target species as well as on the identity and role of other species in the community.     

Deep chlorophyll maxima and UVR acclimation by epilimnetic phytoplankton

1. It is well established that ultraviolet radiation (UVR) has many harmful effects on phytoplankton, but the factors controlling algal sensitivity to UVR are not fully understood. 2. We exposed phytoplankton communities from the epilimnia and deep chlorophyll maxima (DCM) of 2 Canadian lakes to 14 irradiance treatments of various spectral quality and monitored changes in the maximum quantum efficiency of Photosystem II photochemistry (F_v/F_m) using a pulse amplitude modulation fluorometer. 3. Phytoplankton from DCM did not show marked differences from epilimnetic communities in taxonomy or nutrient status, but exhibited substantially higher photosynthetic impairment under UVR exposure. 4. Our results suggest that epilimnetic phytoplankton acclimate to in situ light conditions in a spectrally‐specific manner, and that ultraviolet‐A radiation is a stronger stressor than ultraviolet‐B or photosynthetically active radiation in the mixed layers of our study lakes. Model estimates of damage and recovery rate constants revealed that the phytoplankton of the two lakes relied upon different strategies of UVR‐acclimation, in one lake minimising susceptibility to photodamage and in the other maximising recovery efficiency.     

Interference by Cellular Melanin With Assay of DNA-Protein Crosslinks by the Potassium Dodecyl Sulfate Precipitation Method

The potassium dodecyl sulfate precipitation method was used to quantify DNA-protein crosslinks (DPCs) in lysates of melanoma cells exposed to ultraviolet radiation. Inducing melanin production in these cells before exposure to ultraviolet radiation decreased the apparent yield of DPCs. The decrease could also be produced by addition of melanin to lysates after exposure to crosslinking conditions. Experimental models could attribute this decrease to neither quenching of scintillations from the tritium label used nor to an effect of single strand breaks of DNA. This assay appears to be inappropriate for quantification of DPCs in melanized cells.     

UV-B effects on microplankton communities in Kongsfjord, Svalbard - A mesocosm experiment

The effect of ambient ultraviolet radiation on microplankton communities in an Arctic fjord was measured in mesocosms incubated for 9 days at 2 or 5 meters depth. The mesocosms were either shielded from UV-B radiation by Mylar foil or received full radiation. The parameters measured were: microscopic counts of phytoplankton and micro-zooplankton, photosynthetic capacity, the wavelength-dependent inhibition of photosynthesis, and bacterial biomass and production. The results showed that UV-B radiation increased the photosynthetic capacity of the community but that the overall biomass of the plankton community was reduced. This indicates that UV-B exposure results in a net impairment of the plankton community in that it reduces the potential to allocate the photosynthetic product into new biomass or that the grazing pressure is higher in the UV-B exposed mesocosms. There were no differences in the wavelength dependence between communities exposed to UV-B versus not, but we observed a significantly lower dependence in communities from 2 m depth compared to those from 5 m, indicating that an acclimation of the photosynthetic apparatus to high radiation also reduces the wavelength dependence. A general effect was an increase in nanoflagellate and choanoflagellate biomass and a decreased in the biomass of ciliates and bacteria. The increase nanoflagellates was significantly larger in mesocosms shielded from UV-B, while choanoflagellates increased more in UV-B exposed mesocosms.     

THE EFFECTS OF ULTRAVIOLET RADIATION ON SPORES OF THE FUNGUS ASPERGILLUS NIGER

The survival ratio of Aspergillus spores exposed to ultraviolet radiation has been measured as a function of total incident energy for wave lengths of 2537 Å, 3022 Å, 3129 Å, and 3650 Å. The effect of humidity on killing of Aspergillus spores by ultraviolet radiation has been found to be negligible. A delay in germination as a result of irradiation has been found. The Bunsen-Roscoe reciprocity law has been found to hold within the limits of the radiation intensities studied. Certain morphological changes have been observed.     

Is the lens canned?

The ocular lens somehow remains pellucid despite bombardment by ultraviolet radiation and endogenous hydrogen peroxide (present in the humoral fluids which bathe this tissue). The lens and adjacent aqueous and vitreous humors contain exceptionally high concentrations of reducing substances, particularly ascorbic acid, thought to be important in lenticular oxidant defense. However, in the presence of traces of transition metals, or when exposed to ultraviolet radiation, ascorbic acid readily reacts with oxygen, yielding hydrogen peroxide, and damaging lens crystallins. We propose the alternative hypothesis that the real antioxidant function of ascorbic acid, particularly that in the aqueous and vitreous humors, may be effecting the conversion of oxygen to water. Because the lens lacks a blood supply, coupled reactions of ascorbic acid with oxygen in the humoral fluid spaces should produce a metabolically sustained anaerobiosis. If so, nature may have preinvented the process of canning, wherein food (or in this case, the lens) is preserved by a combination of sterility and anoxia.