Effects of solar and artificial radiation on motility and pigmentation in Cyanophora paradoxa

The effects of solar radiation and artificial UV irradiation on motility and pigmentation were studied in the flagellate system Cyanophora paradoxa. Both percentage of motile cells and average velocity decreased drastically after a solar exposure of a few hours. This effect was not due to an overheating since the cells were exposed under temperaturecontrolled conditions. Partial reduction of the UV-B radiation by cut-off filters or by insertion of an artificial ozone layer increased the tolerated exposure times. Artificial UV radiation also induced the same effects. Under both solar and artificial UV irradiation the photosynthetic pigments within the cyanelles were bleached also within short exposure times. Kinetics of pigment destruction showed that the accessory phycobilins are lost with a half life of 1.3 h while the chlorophylls had a half life of 33 h and a carotenoid with an absorption maximum at 480 nm of 17.3 h.     

Effects of Solar Radiation on Photoorientation,Motility and Pigmentation in a Freshwater Cryptomonas

The effects of solar radiation on motility, photoorientation and pigmentation have been studied in a freshwater Cryptomonas species. The diaphototactic orientation performed by the cells is impaired within about 90 min of solar radiation. Likewise, the percentage of motile cells within the population and the average velocity of the swimming cells decreases within about the same exposure time. This effect is not due to a thermal stress but rather seems to be caused by the solar UV-B component, since decreasing short wavelength UV radiation by means of an artificial ozone filter or UV cut-off filters increased the tolerated exposure time. Solar radiation also bleached the photosynthetic pigments of the cells as shown by absorption difference spectra.     

Ultraviolet-B inhibition of motility in green and dark bleachedEuglena gracilis

The motility of green and dark bleachedEuglena gracilis was studied under artificial and solar UV-B radiation. The percentage of motile cells in the population was drastically impaired after exposure to unfiltered sunlight for only a few hours. Dark bleached cells were even more affected than green organisms. The effect is caused mainly by the solar UV-B component, since filtering the sunlight by either a layer of ozone or a UV-B-absorbing filter substantially increased the survival rate. Addition ofp-quinone, a scavenger of free radicals produced in a type I photodynamic reaction, did not relieve the UV-B effects, but was cytotoxic at higher concentrations. Likewise, 1,4-diazobicyclo[2,2,2]octane and imidazole, which quench singlet oxygen (¹O₂) generated in a type II photodynamic reaction, did not prolong the survival in UV-B irradiation. D₂O, which, in contrast, prolongs the lifetime of¹O₂, is tolerated by the cells but does not aggravate the UV-B inhibition. Thus, photodynamic processes of both type I and II can be ruled out as possible mechanisms of UV-B inhibition of motility inEuglena gracilis.     

UV protectants for the biopesticide based on Bacillus sphaericus Neide and their role in protecting the binary toxins from UV radiation

The UV protectant properties of 26 natural and synthetic compounds were investigated for a biopesticide based on an indigenously isolated strain (ISPC-8) of Bacillus sphaericus Neide. In initial screening, spores of ISPC-8 with 0.1% (w/w for solid and v/w for liquid materials) concentration of different compounds were exposed to UV-B radiation (4.9 × 10⁵ J/m²) for 6 h and their spore viability and larvicidal activity were studied. The larvicidal activity was evaluated against third-instar larvae of Culex quinquefasciatus Say. There was a complete loss of spore viability (1.4% viable spores) and partial reduction in larvicidal activity (57.7% of original activity) after exposure of spores to UV-B for 6 h. However, spore viability as well as larvicidal activity protected significantly when spores were mixed with different compounds before exposing them to UV-B. Among the different compounds tested benzaldehyde, congo red, para-aminobenzoic acid (PABA) and cinnamaldehyde were found to be promising in protecting the spores from UV-B radiation. The presence of binary toxins (41.9 kDa and 51.4 kDa) in protected and unprotected samples were examined by SDS–PAGE. The binary toxin bands disappeared in unprotected spores after 24 h of exposure to UV-B, whereas toxin bands were distinctly visible when spores with benzaldehyde and cinnamaldehyde were exposed to UV-B for 96 h and 120 h, respectively. Congo red and PABA were found to be most effective in protecting binary toxins even after 168 h of exposure to UV-B. Incorporation of these promising UV protectant compounds in biopesticides would help in protecting the spores from the adverse effects of UV radiation and prolong the persistence of biopesticides under field conditions.     

Inhibition of photosynthesis by UV-B exposure and its repair in the bloom-forming cyanobacterium <Emphasis Type="Italic">Microcystis aeruginosa</Emphasis>

The photosynthetic performance of Microcystis aeruginosa FACHB 854 during the process of UV-B exposure and its subsequent recovery under photosynthetic active radiation (PAR) was investigated in the present study. Eight hours UV-B radiation (3.15 W m⁻²) stimulated the increase of photosynthetic pigments content at the early stage of UV-B exposure followed by a significant decline. It suggested that UV-B damage was not an immediate process, and there existed a dynamic balance between damage and adaptation in the exposed cells. Short-term UV-B exposure severely inhibited the photosynthetic capability, but it could restore quickly after being transferred to PAR. Further investigations revealed that the PS II of M. aeruginosa FACHB 854 was more sensitive to UV-B exposure than PS I, and the oxygen-evolving complex of PS II was an important damage target of UV-B. The inhibition of photosynthetic performance caused by UV-B could be recovered to 90.9% of pretreated samples after 20 h exposure at low PAR, but it could not be recovered in the dark as well as under low PAR in the presence of Chloromycetin. It can be concluded that PAR and de novo protein synthesis were essential for the recovery of UV-B-damaged photosynthetic apparatus.     

The impact of ultraviolet-B radiation on the motility of the freshwater epipelic diatom Nitzschia lineariz

Depletion of the stratospheric ozone layer has been of increased concern due to correlated increases in ambient ultraviolet radiation. Our research investigated the diel response of the motile behaviour of Nitzschia lineariz in both natural (freshwater stream) and experimental conditions. We classified the behaviour of individual diatom cells as gliding, immobile and oscillating. The experimental conditions were of simultaneous exposure either to net ambient solar radiation (control) or to ambient plus enhanced UV-B levels (treatment). UV-B for the control condition was filtered out using polyester filters; cells exposed to UV-B were irradiated through cellulose diacetate filters. UVB-313 levels were augmented to 33% (290 mW m^–2) and 66% (365 mW m^–2) above the local average ambient levels (220 mW m^–2) for 10 h. The mobile behaviour of cells was examined and quantified every 2 consecutive hours from dawn to dusk in subsampled populations. The number of gliding cells in subsample populations declined on overcast days at both the 33 and 66% UV-B enhancement levels, whereas the number of immobile and oscillating cells increased with increased UV-B exposure. On sunny days, mobile behaviour was not affected at either enhancement level, which suggests that cellular repair mechanisms may be activated during sunny conditions.     

Response of the estuarine cyanobacterium <Emphasis Type="Italic">Lyngbya aestuarii</Emphasis> to UV-B radiation

Growth response and changes in the spectral properties of methanolic extract of an estuarine cyanobacterium, Lyngbya aestuarii Agardh, to UV-B radiation were studied. Increase in growth accompanied by increase in chlorophyll a, protein and carbohydrate content was observed up to 12 h of UV-B irradiation followed by a decline with further increase in the duration of UV exposure. Carotenoid content progressively increased with the UV-B dose. The organism synthesized, to a significant extent, mycosporine amino acid-like substances (MAAs) upon UV-B exposure. The cells in the trichome became coiled followed by formation of small bundles as a response to UV-B radiation. SDS protein profile of the UV irradiated cells showed repression of 20 and 22 kDa proteins. However, irradiation with UV-B for 6–24 h led to overproduction of 84, 73, 60, 46, 40, 37 KDa proteins, possibly conferring protection to the organism from UV-B. UV irradiated cells cultured in florescent light for up to 7 days showed revival from UV damage of the pigments and macromolecular contents, suggesting existence of a repair mechanism in the organism.     

Differential responses of Nostoc sphaeroides and Arthrospira platensis to solar ultraviolet radiation exposure

During October to December 2003 we carried out experiments to assess the impact of high solar radiation levels (as normally occurring in a tropical region of Southern China) on the cyanobacteria Nostoc sphaeroides and Arthrospira (Spirulina) platensis. Two types of experiments were done: a) Short-term (i.e., 20 min) oxygen production of samples exposed to two radiation treatments (i.e., PAR+UVR—280–700 nm, and PAR only—400–700 nm, PAB and P treatments, respectively), and b) Long-term (i.e., 12 days) evaluation of photosynthetic quantum yield (Y) of samples exposed to three radiation treatments (i.e., PAB; PA (PAR+UV-A, 320–700 nm) and P treatments, respectively). N. sphaeroides was resistant to UVR, with no significant differences (P>0.05) in oxygen production within 20 min of exposure, but with a slight inhibition of Y within hours. A fast recovery of Y was observed after one day even in samples exposed to full solar radiation. A. platensis, on the other hand, was very sensitive to solar radiation (mainly to UV-B), as determined by oxygen production and Y measurements. A. platensis had a circadian rhythm of photosynthetic inhibition, and during the first six days of exposure to solar radiation, it varied between 80 and 100% at local noon, but cells recovered significantly during afternoon hours. There was a significant decrease in photosynthetic inhibition after the first week of exposure with values less than 50% at local noon in samples receiving full solar radiation. Samples exposed to PA and P treatments recovered much faster (within 2–3 days), and there were no significant differences in Y between the three radiation treatments when irradiance was low (late afternoon to early morning). Long-term acclimation seems to be important in A. platensis to cope with high UVR levels however, it is not attained through the synthesis of UV-absorbing compounds but it seems to be mostly related to adaptive morphological changes.     

Regulation of enzymes involved in C4 photosynthesis and the antioxidant metabolism by UV-B radiation in Egeria densa,a submersed aquatic species

Egeria densa, a submersed aquatic species, was exposed to different treatments under UV-B radiation, and the response of phosphoenolpyruvate carboxylase (PEPC) and NADP-malic enzyme (NADP-ME) was determined. Exposure to UV-B radiation for 4 h per day over 7–16 days caused an increase in both enzymes, together with an increase in the activity of some isoforms of several enzymes involved in the antioxidant metabolism, such as superoxide dismutase (SOD), ascorbate peroxidase (APX), catalase (CAT) and peroxidase (POD). The content of chlorophylls and carotenoids was considerably decreased, suggesting that degradation or repression of the synthesis of these molecules may be occurring after UV-B exposure. Reactive oxygen species (ROS) were also required for UV-B induction of PEPC and NADP-ME, as the addition of ascorbic acid before UV-B treatment prevented the induction of these enzymes, while salicylic acid was not effective in inducing NADP-ME but increased the expression of the lower molecular mass isoform of PEPC. On the other hand, damage to the photosynthetic machinery may be occurring after exposure to UV-B radiation for 8 per day over 1–2 days, as indicated by a decrease in the levels of Rubisco, PEPC and NADP-ME. Some of the enzymes involved in the antioxidant metabolism, such as CAT and APX, were also sensitive to continuous exposure, evidenced by a decrease in their activity. In this way, in E. densa, several enzymes involved in different metabolic pathways showed a distinct response, depending on the UV-B treatment. This revised version was published online in June 2006 with corrections to the Cover Date.     

Reduced digestibility of UV-B stressed and nutrient-limited algae by Daphnia magna

Daphnia magna was fed the green alga Selenastrum capricornutum, cultured under four different growth conditions: (1) phosphorus limitation, (2) nitrogen limitation, (3) UV-B irradiation, and (4) no nutrient limitation, no UV-B irradiation. Contrary to non-limited algal cells, nutrient-limited cells were not efficiently assimilated. Especially, P-limited cells passed through the gut mostly intact, while N-limited cells were partly assimilated. Also, algae exposed to moderate doses of UV-B radiation (0.3 mW cm^–2 of UV₃₁₂) were less efficiently assimilated after being grazed. Digestibility of the algae decreased with increased UV-B exposure time. Nutrient-limited and UV-B stressed algal cells increased in volume and became granular in appearance. These changes in the algal cells, combined with changed cell wall properties, most probably reduced their digestibility.     

Effect of UV Irradiance on Utilization of Inorganic Nitrogen by the Antarctic Diatom Odontella weissflogii (Janisch) Grunow

Abstract: The impact of UV-B irradiation on unialgal cultures of the temperate marine diatom Odontella sinensis and of the Antarctic Odontella weissflogii was tested under controlled laboratory conditions. Uptake rates of inorganic nitrogen by Odontella sinensis were more affected by UV-B radiation than those of Odontella weissflogii. Utilization of ¹⁵N-ammonium was reduced after 3 h of UV-B exposure. Values of K_m from several marine phytoplankton species were estimated from algae not exposed to UV-B and from those after 3 h of UV-B radiation. Calculation of Lineweaver-Burk plot showed, under UV-B stress, a noncompetitive inhibition for ¹⁵NH⁺₄ uptake and a competitive inhibitory effect for ¹⁵NO^?₃ by Odontella weissflogii. The damage to ¹⁵NH⁺₄ uptake by UV-B was more pronounced under red than blue light; a contradictory result was obtained for ¹⁵NO^?₃ utilization by Odontella weissflogii. Reduction of the pigments by UV-B under white light was dependent on the exposure time; a strong depression of the contents of chlorophyllide a, chlorophyll c, diatoxanthin and the fucoxanthins was found. Contents of the chlorophylls are markedly affected by UV-B under red light whereas the chlorophyll a concentration is enhanced in blue and green light. UV-B exposure in conjunction with blue and green light led to a reduction of the protein content and an increase in the amino acid contents. The pattern of pool sizes of free amino acids varied after UV-B exposure. UV-A irradiance had no effect. The possible targets of UV-B irradiation on the uptake system of inorganic nitrogen are discussed in detail. Adaptation to the environmental conditions, e.g. via synthesis of UV stress proteins or mycosporine-like amino acids, were also considered.     

Effects of UV-B on motility and photobehavior in the green flagellate,Euglena gracilis

UV-B inhibits the motility of the green flagellate, Euglena gracilis, at fluences rates higher than those expected to occur in the natural sunlight even when the stratospheric ozone layer is partially reduced by manmade pollutants. The phototactic orientation of the cells, however, is drastically impaired by only slightly enhanced levels of UV-B irradiation. Since only negative phototaxis (movement away from a strong light source) is impaired while positive phototaxis (movement toward a weak light source) is not, the delicate balance by which the organisms adjust their position in their habitat is disturbed. Under these conditions the cells are unable to retreat from hazardous levels of radiation and are eventually killed not by the UV-B irradiation but by photobleaching of their photosynthetic pigments in the strong daylight at the surface.     

The impact of food quantity on UV-B tolerance and recovery from UV-B damage in Daphnia pulex

UV-B (290 nm) tolerance of Daphnia pulex, conditioned to four different food levels (Chlorophyta), was tested under standardized conditions with an artificial radiation source. Parameters measured were survival, percentage of egg bearing Daphnia and the number of juveniles produced after irradiation. UV-B tolerance of Daphnia pulex was found to be significantly improved with increasing food concentrations at all three parameters. The impact of the four different food concentrations on the photoreactivation system was tested with simultanous UV-B and white-light irradiation of Daphnia. Survival rate improved significantly with increasing food levels compared to solely UV-B irradiation. Photoreactivation had no effect on the reproductive parameters.     

Effects of Ultraviolet and X-Ray Radiation on in vitro Cultivated Cells of Haplopappus gracilis

A cell strain of Haplopappus gracills was used for investigations of the effects of UV (2537 A) and X-ray irradiation. Mitotic inhibition and killing after UV exposure were studied. A survival curve of UV treated and then plated cells is presented. The LD₅₀ seems to be about 2000 erg. mm^?2 under the experimental conditions used. All types of chromosome aberrations are induced by UV irradiation, but the frequency is relatively low at doses which do not completely inhibit cell division. A mutant strain of chromosome type is isolated after UV treatment and then plating. Mitotic inhibition and killing after X-ray treatment were studied. A survival curve is presented and the LD₅₀ under the culture conditions used seems to be about 2000 R. The frequency of chromosome aberrations induced by X-rays is highly increased by aeration during X-ray treatment which indicates that some degree of cell anoxia exists in a cell suspension. There arr indications that chromosome aherrations may not cause growth inhibition to such an extent as is usually believed.     

Inhibition of hypocotyl elongation by ultraviolet-B radiation in de-etiolating tomato seedlings. II. Time-course, comparison with flavonoid responses and adaptive significance

UV-B radiation inhibits hypocotyl elongation in etiolated tomato (Lycopersicon esculentum Mill. cv. Alisa Craig) seedlings acting through a photoreceptor system with peak apparent effectiveness around 300 nm. In order lo further characterize the response and gain insight into its potential ecological significance, the time-course of inhibition was measured and compared with the time-course of flavonoid accumulation in the same seedlings. When a background of strong (> 620 μmol m^?2 s^?1) white light (WL) was supplemented with low irradiance UV-B (～ 3 μmol m^?2 s^?1). substantial (～ 50%) inhibition of elongation occurred within 3 h of the light treatment. The magnitude of UV-B-induced elongation inhibition was similar in wild type (WT) and au-mutant seedlings, in spite of the large differences between genotypes in rate and temporal pattern of elongation. In comparison to the effect of UV-B on elongation, induction of flavonoid accumulation in WT and au seedlings undergoing de-etiolation was a much slower response. Several UV-absorbing compounds appeared to be specifically induced by light, and some of them accumulated faster under the WL + UV-B treatment than under WL alone. However, there was little or no delectable effect of WL on flavonoid levels until up to 3 h of treatment, and the specific UV-B effect was measurable only after 6 h of continuous treatment. Indeed. UV-B-screening properties of crude alcoholic extracts were not different between WL and WL + UV-B treatments until after 9 or 24 h. When the light treatments were applied to seedlings that were just breaking through the soil surface. UV-B was found to consistently retard seedling emergence. These results suggest that the rapid inhibition of elongation in de-etiolating seedlings is an evolved response lo UV-B, which may serve to minimize seedling exposure to sunlight until protective pigmentation responses (triggered by WL and UV-B) have taken place in the seedlings epidermis.     

Motile tubular vacuoles in extramatrical mycelium and sheath hyphae of ectomycorrhizal systems

Summary Extramatrical mycelium and outer hyphae of the sheath ofEucalyptus pilularis-Pisolithus tinctorius mycorrhizas contain abundant motile tubular vacuoles which accumulate the carboxyfluorescein analogue Oregon Green 488 carboxylic acid. The fluorochrome accumulates in a system of small vacuoles, tubules, and larger vacuoles, which are interlinked, motile, and pleiomorphic, in external hyphae, cords, and hyphae of the outer sheath. There is often a difference in fluorescence between two neighbouring cells, indicating that the dolipore septum exercises control on the movement of material between cells. Generally the motile tubular vacuole system in mycorrhizas resembles that previously found in isolated mycelium. The majority of fungal cells in the sheath contain no fluorochrome even after long exposure of the mycorrhiza to the solution, but with differential interference optics the cells are clearly seen to be alive and to contain vacuoles resembling those in the outer hyphae. In translocation experiments, long-distance transport of the fluorochrome is slow and slight, or even nonexistent in some cases.Abbreviations carboxy-DFF Oregon Green 488 carboxylic acid - carboxy-DFFDA Oregon Green 488 carboxylic acid diacetate - DIC differential interference contrast Dedicated to Professor Brian E. S. Gunning on the occasion of his 65th birthday     

The response of Ceratophyllum demersum L. and Myriophyllum spicatum L. to reduced, ambient, and enhanced ultraviolet-B radiation

The response of Ceratophyllum demersum and Myriophyllum spicatum to three levels of UV-B radiation – reduced (ca. 50% reduction), ambient and enhanced UV-B radiation, simulating 17% ozone depletion – is discussed. The research revealed that UV-B stimulated the production of UV-B absorbing compounds in C. demersum, but not in M. spicatum. The relative amount of UV-B absorbing compounds was about four times lower in C. demersum. Enhanced UV-B also affected respiratory potential in C. demersum (on average 3.7 mg O₂/gDM/h), but no effect on M. spicatum (on average 5.5 mg O₂/gDM/h) was detected. Increased need for energy revealed that UV-B radiation exerted stress in C. demersum. No changes in chlorophyll a and no disturbance to photochemical efficiency due to UV-B were observed in either species.     

Interspecific Variability in Sensitivity to UV Radiation and Subsequent Recovery in Selected Isolates of Marine Bacteria

The interspecific variability in the sensitivity of marine bacterial isolates to UV-B (295- to 320-nm) radiation and their ability to recover from previous UV-B stress were examined. Isolates originating from different microenvironments of the northern Adriatic Sea were transferred to aged seawater and exposed to artificial UV-B radiation for 4 h and subsequently to different radiation regimens excluding UV-B to determine the recovery from UV-B stress. Bacterial activity was assessed by thymidine and leucine incorporation measurements prior to and immediately after the exposure to UV-B and after the subsequent exposure to the different radiation regimens. Large interspecific differences among the 11 bacterial isolates were found in the sensitivity to UV-B, ranging from 21 to 92% inhibition of leucine incorporation compared to the bacterial activity measured in dark controls and from 14 to 84% for thymidine incorporation. Interspecific differences in the recovery from the UV stress were also large. An inverse relation was detectable between the ability to recover under dark conditions and the recovery under photosynthetic active radiation (400 to 700 nm). The observed large interspecific differences in the sensitivity to UV-B radiation and even more so in the subsequent recovery from UV-B stress are not related to the prevailing radiation conditions of the microhabitats from which the bacterial isolates originate. Based on our investigations on the 11 marine isolates, we conclude that there are large interspecific differences in the sensitivity to UV-B radiation and even larger differences in the mechanisms of recovery from previous UV stress. This might lead to UV-mediated shifts in the bacterioplankton community composition in marine surface waters.     

Pattern of Proteins after Heat Shock and UV-B Radiation of some Temperate Marine Diatoms and the Antarctic Odontella weissflogii

Synthesis of stress proteins after heat shock and different periods of UV-B radiation were investigated with marine diatom species from the North Sea Ditylum brightwellii, Lithodesmium variabile, Odontella sinensis, Thalassiosira rotula and the Antarctic diatom Odontella weissfloggii from the Weddell Sea. Algae were grown in an artifical sea-water medium under controlled laboratory conditions: light/dark regime of 12:12 h (7.2 W m^?2), normal air (0.035 vol.% CO₂) and 18° or 4 °C. All the tested diatom species can produce heat shock proteins (HSPS) of the 70 kDa family by in vivo labelling with [³⁵S]-methionine. The same results were obtained for Odontella sinensis, Ditylum brightwellii and Odontella weissflogii by estimation of the in vitro translation products with poly-A-mRNA isolated from these organisms. However, Odontella weissflogii, a species relatively insensitive to UV-B irradiance, did not synthesize UV-induced HSPS, whereas the UV-sensitive diatom Odontella sinensis, as well as Lithodesmium variabile, produced all the observed HSPS after UV-B exposure. In addition, a protein of 43 kDa was found after UV-B irradiance of the temperate Odontella sinensis. The temperate marine diatom Thalassiosira rotula synthesized 70 kDa and 5 7 kDa proteins after a heat shock and a UV-B exposure of 2 h, but a 40 kDa protein could not be detected, whereas a 60 kDa protein was found after 2 h UV-B exposure. The results are discussed in view of a possible adaptation of O. weissflogii to an enhanced UV dose.