Wavelength dependence of mycosporine-like amino acid synthesis in Gyrodinium dorsum

The synthesis or accumulation of mycosporine-like amino acids (MAAs) is an important UV tolerance mechanism in aquatic organisms. To investigate the wavelength dependence of MAA synthesis in the marine dinoflagellate Gyrodinium dorsum, the organism was exposed to polychromatic radiation (PAR and UV) from a solar simulator for up to 72 h. Different irradiance spectra were produced by inserting various cut-off filters between lamp and samples. A polychromatic action spectrum for the synthesis of MAA synthesis was constructed. PAR and long wavelength UV-A radiation showed almost no effect while the most effective wavelength range was around 310 nm. Shorter wavelengths where less effective in the induction of MAA synthesis. Wavelengths below 300 nm damaged the organisms severely as indicated by a decrease in chlorophyll a absorption.     

Mycosporine-like Amino Acids Provide Protection Against Ultraviolet Radiation in Eggs of the Green Sea Urchin Strongylocentrotus droebachiensis

A photoprotective role of ultraviolet radiation-absorbing mycosporine-like amino acids (MAAs) in eggs of the green sea urchin Strongylocentrotus droebachiensis was demonstrated by comparing UV-induced delays in the first division of embryos having either high or low concentrations of MAAs. Embryos from adult urchins fed Laminaria saccharina (no MAAs) had low concentrations of MAAs and experienced a significantly longer UV-induced delay in cleavage (25.1%) than MAA-rich embryos from adults fed Mastocarpus stellatus (12.8% delay) or a combination diet of both macroalgae (12.3% delay). Collectively, these embryos displayed a significant inverse logarithmic relationship between MAA concentration and percentage cleavage delay, so that the greater the MAA concentration in the eggs, the less they were affected by UV radiation. This is the first study to examine such MAA manipulation of cellular MAA concentrations with no prior UV exposure of the experimental subjects. Concentrations of MAAs were also measured in unfertilized eggs, blastulae, gastrulae and early pluteus larvae, providing the first documentation of changes in MAAs during embryological and larval development. The concentration of shinorine (the principal MAA in the eggs) did not change during short-term UV exposure in vivo or long-term exposure in vitro; such photostability is a useful attribute of a natural sunscreen.     

UV-B-induced synthesis of mycosporine-like amino acids in three strains of Nodularia (cyanobacteria)

Three filamentous and heterocystous cyanobacterial strains of Nodularia, Nodularia baltica, Nodularia harveyana and Nodularia spumigena, have been tested for the presence and induction of ultraviolet-absorbing/screening mycosporine-like amino acids (MAAs) by simulated solar radiation in combination with 395 (receiving photosynthetically active radiation (PAR) only), 320 (receiving PAR + UV-A) and 295 (receiving PAR + UV-A + UV-B) nm cut-off filters. Absorption spectroscopic analyses of the methanolic extracts of samples revealed a typical MAA peak at 334 nm in all three cyanobacteria. Specific contents of MAAs had a pronounced induction in the samples covered with 295 nm cut-off filters after 72 h of irradiation. In comparison, there was little induction of MAAs in the samples covered by 395 and 320 nm cut-off filters. High performance liquid chromatographic (HPLC) studies revealed the presence of two types of MAAs in all three cyanobacteria, which were identified as shinorine and porphyra-334, both absorbing maximally at 334 nm. The occurrence of porphyra-334 is rare in cyanobacteria. Specific content of both shinorine and porphyra-334 were induced remarkably only in the samples covered with 295 nm cut-off filters. The results indicate that in comparison to UV-A and PAR, UV-B is more effective in eliciting MAAs induction in the studied cyanobacteria.     

Effect of UV-B Radiation and Desiccation Stress on Photoprotective Compounds Accumulation in Marine <Emphasis Type="Italic">Leptolyngbya</Emphasis> sp.

Increased awareness regarding the harmful effects of ultraviolet (UV)-B radiation has led to the search for new sources of natural UV-B protecting compounds. Mycosporine-like amino acids are one of such promising compounds found in several organisms. Cyanobacteria are ideal organisms for isolation of these compounds due to their compatibility and adaptability to thrive under harsh environmental conditions. In the following investigation, we report the production of shinorine in Leptolyngbya sp. isolated from the intertidal region. Based on the spectral characteristics and liquid chromatography-mass spectrometry analysis, the UV-absorbing compound was identified as shinorine. To the best of our knowledge, this is the first report on the occurrence of shinorine in Leptolyngbya sp. We also investigated the effect of artificial UV-B radiation and periodic desiccation on chlorophyll-a, total carotenoids, and mycosporine-like amino acids (MAAs) production. The UV-B radiation had a negative effect on growth and chlorophyll concentration, whereas it showed an inductive effect on the production of total carotenoids and MAAs. Desiccation along with UV-B radiation led to an increase in the concentration of photoprotective compounds. These results indicate that carotenoids and MAAs thus facilitate cyanobacteria to avoid and protect themselves from the deleterious effects of UV-B and desiccation.     

Photoprotection and long-term acclimation to UV radiation in the marine diatom Thalassiosira weissflogii.

Unialgal cultures of the marine diatom Thalassiosira weissflogii (Grunow) were exposed for 40 days to artificial UV-B radiation in the presence of PAR and UV-A to examine long-term acclimation to UV, PAR and UV-A were supplied 14 h daily, while UV-B (two levels: 0.16 and 0.30 W m(-2) unweighted) was supplied for 4 h/day. Growth rates and photochemical capacity (CFC ratio) both decreased over the first 10-15 days, then recovered. No obvious differences were noted between the responses to the two UV-B treatments. The concentration of the major pigments (chlorophyll a and c(1+2), fucoxanthin and beta,beta-carotene) changed very little with time, except for diatoxanthin. which increased over the first 16 days, decreased over the next 13 days, then increased again from day 29 to the end of the experiment. The concentration of total mycosporine-like amino acids (MAAs) was initially undetectable, then increased from day 16 in the high UV-B treatment and after day 22 in the low UV-B treatment, reaching a maximum on day 29 for both treatments and decreasing afterwards. The synthesis of MAAs proceeded only once photochemical capacity had recovered from the initial UV stress and this recovery likely involved the xanthophyll cycle (diatoxanthin increase). The concentration of MAAs decreased when the cells showed signs of photoinhibition (decrease in CFC ratio). It also showed an inverse trend with diatoxanthin. UV-B alone had little regulatory effect over these responses, except possibly for an earlier synthesis of MAAs under HUV-B conditions. This suggests that the observed changes were due to UV-A rather than to UV-B exposure. The overall response of this coastal diatom to prolonged UV exposure indicates that T. weissflogii is a relatively UV-tolerant species and that its long-term response to UV exposure involves an activation of the xanthophyll cycle followed by the synthesis of MAAs, which may proceed only when photoinhibition is relieved.     

Induction of mycosporine-like amino acids (MAAs) in cyanobacteria by solar ultraviolet-B radiation

Three filamentous and heterocystous N₂-fixing cyanobacteria, Anabaena sp., Nostoc commune and Scytonema sp. were tested for the presence of ultraviolet-absorbing mycosporine-like amino acids (MAAs) and their induction by solar ultraviolet-B (UV-B) radiation. High performance liquid chromatographic (HPLC) studies revealed the presence of only one type of MAAs in all three cyanobacteria, that was identified as shinorine, a bisubstituted MAA containing both glycine and serine groups having an absorption maximum at 334 nm and a retention time of around 2.8 min. There was a circadian induction in the synthesis of MAAs when the cultures were exposed to mid-latitude solar radiation (Playa Unión, Rawson, Chubut, Patagonia, Argentina) for 3 days, 4–6th February, 2000. Solar radiation was measured by an ELDONET (European Light Dosimeter Network) filter radiometer permanently installed on the roof of the Estación de Fotobiología Playa Unión (43°18′ S; 65°03′ W). The maximum irradiances were around 450–500, 45–50 and 1.0–1.2 W m⁻² for PAR (photosynthetic active radiation), UV-A (ultraviolet-A) and UV-B (ultraviolet-B), respectively. PAR and UV-A had no significant impact on MAA induction while UV-B induced the synthesis of shinorine in all three cyanobacteria. Shinorine was found to be induced mostly during the light period. During the dark period the concentration stayed almost constant. In addition to shinorine, another unidentified, water-soluble, brownish compound with an absorption maximum at 315 nm was found to be induced by UV-B only in Scytonema sp. and released into the medium. This substance was neither found in Anabaena sp. nor in Nostoc commune. Judging from the results, the studied cyanobacteria may protect themselves from deleterious short wavelength radiation by their ability to synthesize photoprotective compounds in response to UV-B radiation.     

Mycosporine-like Amino Acids in Freshwater Copepods: Potential Sources and Some Factors That Affect Their Bioaccumulation

Mycosporine-like amino acids (MAAs) are ubiquitous photoprotective compounds in aquatic environments. MAAs are synthesized by a wide variety of organisms (i.e. bacteria, fungi and algae) and their production is photoinducible by ultraviolet radiation (UVR) (280–400 nm) and/or photosynthetically active radiation (400–750 nm). Most animals however, are unable to synthesize MAAs and must acquire these compounds through their diet or from symbiotic organisms. In this paper, we investigate the possible sources of MAAs and factors (temperature and initial MAA concentration) that may affect their bioaccumulation in freshwater copepods. We found that MAA accumulation may occur even if the copepods are cultured on a MAA-free diet. In addition, we found that the bacteriostatic antibiotic, chloramphenicol, inhibits the bioaccumulation of MAAs. These two pieces of evidence suggest that the source of MAAs in these copepods may be prokaryotic organisms in close association with the animals. The two factors investigated in this study, temperature and initial MAA concentrations, were found to affect the rates at which MAAs are accumulated. Temperature had positive effects on both uptake and elimination rates. On the other hand, the rate of uptake decreased at the highest assayed initial MAA concentration, probably because the concentration of MAAs was already close to saturation.     

Effects of abiotic stressors on synthesis of the mycosporine-like amino acid shinorine in the Cyanobacterium Anabaena variabilis PCC 7937

In the present investigation we show that the cyanobacterium Anabaena variabilis PCC 7937 produces a single mycosporine-like amino acid (MAA), shinorine (retention time = 2.3 min and absorption maximum at 334 nm) when isolated and purified by HPLC. Although there was significant induction of MAA synthesis from its initial value under 395 or 320 nm cutoff filters, MAA induction was significantly more pronounced in samples covered with 295 nm cutoff filters after 72 h of exposure. Heat as a stress factor had no effect on MAA induction with or without UV radiation. In contrast, salt and ammonium treatment had synergistic effects with UV stress. MAA synthesis was also induced by salt and ammonium in a concentration-dependent manner without UV stress in samples covered with 395 nm cutoff filters. The results indicate that MAAs may have other functions in addition to photoprotection in this organism.     

Polychromatic action spectrum for the induction of a mycosporine-like amino acid in a rice-field cyanobacterium, Anabaena sp

A polychromatic action spectrum for the induction of an ultraviolet-absorbing/screening mycosporine-like amino acid (MAA) has been determined in a filamentous and heterocystous nitrogen-fixing rice-field cyanobacterium, Anabaena sp. High-performance liquid chromatographic (HPLC) studies revealed the presence of only one type of MAA, which was identified as shinorine, a bisubstituted MAA containing both glycine and serine groups having a retention time at 2.8 min and an absorption maximum at 334 nm. Exposure of cultures to simulated solar radiation in combination with various cut-off filters (WG 280, 295, 305, 320, 335, 345, GG 400, 420, 455, 475, OG 515, 530, 570, RG 645, 665 and a broad-band filter, UG 11) clearly revealed that the induction of the MAA takes place only in the UV range. Photosynthetic active radiation (PAR) had no significant impact on MAA induction. The ratio of the absorption at 334 nm (shinorine) to 665 nm (chlorophyll a) and the action spectrum also showed the induction of MAA to be UV dependent peaking in the UV-B range at around 290 nm. The results indicate that the studied cyanobacterium, Anabaena sp. may protect itself from deleterious short wavelength solar radiation by its ability to synthesize a mycosporine-like amino acid in response to UV-B radiation and thereby screen the negative effects of UV-B.     

Novel glycosylated mycosporine-like amino acids with radical scavenging activity from the cyanobacterium Nostoc commune

Mycosporine-like amino acids (MAAs) are UV absorbing pigments, and structurally distinct MAAs have been identified in taxonomically diverse organisms. Two novel MAAs were purified from the cyanobacterium Nostoc commune, and their chemical structures were characterized. An MAA with an absorption maximum at 335 nm was identified as a pentose-bound porphyra-334 derivative with a molecular mass of 478 Da. Another identified MAA had double absorption maxima at 312 and 340 nm and a molecular mass of 1,050 Da. Its unique structure consisted of two distinct chromophores of 3-aminocyclohexen-1-one and 1,3-diaminocyclohexen and two pentose and hexose sugars. These MAAs had radical scavenging activity in vitro; the 1050-Da MAA contributed approximately 27% of the total radical scavenging activities in a water extract of N. commune. These results suggest that these glycosylated MAAs have multiple roles as a UV protectant and an antioxidant relevant to anhydrobiosis in N. commune.     

The role of UV-B radiation in aquatic and terrestrial ecosystems--an experimental and functional analysis of the evolution of UV-absorbing compounds

We analysed and compared the functioning of UV-B screening pigments in plants from marine, fresh water and terrestrial ecosystems, along the evolutionary line of cyanobacteria, unicellular algae, primitive multicellular algae, charophycean algae, lichens, mosses and higher plants, including amphibious macrophytes. Lichens were also included in the study. We were interested in the following key aspects: (a) does the water column function effectively as an 'external UV-B filter'?; (b) do aquatic plants need less 'internal UV-B screening' than terrestrial plants?; (c) what role does UV screening play in protecting the various plant groups from UV-B damage, such as the formation of thymine dimers?; and (d) since early land 'plants' (such as the predecessors of present-day cyanobacteria, lichens and mosses) experienced higher UV-B fluxes than higher plants, which evolved later, are primitive aquatic and land organisms (cyanobacteria, algae, lichens, mosses) better adapted to present-day levels of UV-B than higher plants? Furthermore, polychromatic action spectra for the induction of UV screening pigments of aquatic organisms have been determined. This is relevant for translating 'physical' radiation measurements of solar UV-B into 'biological' and 'ecological' effects. From the action spectra, radiation amplification factors (RAFs) have been calculated. These action spectra allow us to determine any mitigating or antagonistic effects in the ecosystems and therefore qualify the damage prediction for the ecosystems under study. We summarize and discuss the main results based on three years of research of four European research groups. The central theme of the work was the investigation of the effectiveness of the various screening compounds from the different species studied in order to gain some perspective of the evolutionary adaptations from lower to higher plant forms. The induction of mycosporine-like amino acids (MAAs) was studied in the marine dinoflagellate Gyrodinium dorsum, the green algal species Prasiola stipitata and in the cyanobacterium Anabaena sp. While visible (400-700 nm) and long wavelength UV-A (315-400 nm) showed only a slight effect, MAAs were effectively induced by UV-B (280-315 nm). The growth of the lower land organisms studied, i.e. the lichens Cladina portentosa, Cladina foliacaea and Cladonia arbuscula, and the club moss Lycopodiumannotinum, was not significantly reduced when grown under elevated UV-B radiation (simulating 15% ozone depletion). The growth in length of the moss Tortula ruralis was reduced under elevated UV-B. Of the aquatic plants investigated the charophytes Chara aspera showed decreased longitudinal growth under elevated UV-B. In the 'aquatic higher plants' studied, Ceratophyllum demersum, Batrachium trichophyllum and Potamogeton alpinus, there was no such depressed growth with enhanced UV-B. In Chara aspera, neither MAAs nor flavonoids could be detected. Of the terrestrial higher plants studied, Fagopyrum esculentum, Deschampsia antarctica, Vicia faba, Calamagrostis epigejos and Carex arenaria, the growth of the first species was depressed with enhanced UV-B, in the second species length growth was decreased, but the shoot number was increased, and in the latter two species of a dune grassland there was no reduced growth with enhanced UV-B. In the dune grassland species studied outdoors, at least five different flavonoids appeared in shoot tissue. Some of the flavonoids in the monocot species, which were identified and quantified with HPLC, included orientin, luteolin, tricin and apigenin. A greenhouse study with Vicia faba showed that two flavonoids (aglycones) respond particularly to enhanced UV-B. Of these, quercetin is UV-B inducible and mainly located in epidermal cells, while kaempferol occurs constitutively. In addition to its UV-screening function, quercetin may also act as an antioxidant. Polychromatic action spectra were determined for induction of the UV-absorbing pigments in three photosynthetic organisms, representing very different taxonomic groups and different habitats. In ultraviolet photobiology, action spectra mainly serve two purposes: (1) identification of the molecular species involved in light absorption; and (2) calculation of radiation amplification factors for assessing the effect of ozone depletion. Radiation amplification factors (RAFs) were calculated from the action spectra. In a somewhat simplified way, RAF can be defined as the percent increase of radiation damage for a 1% depletion of the ozone layer. Central European summer conditions were used in the calculations, but it has been shown that RAF values are not critically dependent on latitude or season. If only the ultraviolet spectral region is considered, the RAF values obtained are 0.7 for the green alga Prasiola stipitata, 0.4 for the dinoflagellate Gyrodinium dorsum, and 1.0 for the cyanobacterium Anabaena sp. In the case of P. stipitata, however, the effect of visible light (PAR, photosynthetically active radiation, 400-700 nm) is sufficient to lower the RAF to about 0.4, while the PAR effect for G. dorsum is negligible. RAFs for some damage processes, such as for DNA damage (RAF=2.1 if protective effects or photorepair are not considered [1]), are higher than those above. Our interpretation of this is that if the ozone layer is depleted, increased damaging radiation could overrule increased synthesis of protective pigments. In addition to investigating the functional effectiveness of the different screening compounds, direct UV effects on a number of key processes were also studied in order to gain further insight into the ability of the organisms to withstand enhanced UV-B radiation. To this end, the temperature-dependent repair of cyclobutane dimers (CPD) and (6-4) photoproducts induced by enhanced UV-B was studied in Nicotiana tabacum, and the UV-B induction of CPD was studied in the lichen Cladonia arbuscula. Also, photosynthesis and motility were monitored and the response related to the potential function of the screening compounds of the specific organism.     

Effects of Salinity and Ultraviolet Radiation on the Bioaccumulation of Mycosporine‐like Amino Acids in Artemia from Lake Urmia (Iran)

We investigated the effects of salinity and artificial UV radiation on the accumulation of mycosporine‐like amino acids (MAAs) in sexual and parthenogenetic Artemia from Lake Urmia. The nauplii hatched from the cysts were cultured until adulthood under two salinities (150 and 250 g L^?1) and two light treatments (PAR and PAR+UVR) in the laboratory. Finally, the Artemia were analyzed for their concentration of MAAs. In most of the cases, the higher salinity level applied was found to increase the MAA concentrations in both Artemia populations significantly. The acquisition efficiency of MAAs in both Artemia populations increased under exposure to UVR‐supplemented photosynthetically active radiation (PAR) compared to those raised under PAR, except for Porphyra‐334. It was observed that combination of UV radiation and elevated salinity significantly increased the bioaccumulation of MAAs. Thus, the presence of these compounds in these populations of Artemia may increase their adaptability for living in high‐UV and high‐salinity conditions prevailing in Lake Urmia. Higher concentrations of MAAs in the parthenogenetic population of Artemia could be probably attributed to its mono sex nature and higher adaptation capacities to extreme environmental conditions.     

A novel prokaryotic UVB photoreceptor in the cyanobacterium Chlorogloeopsis PCC 6912

We present evidence for the presence and nature of a UVB-specific photoreceptor in the cyanobacterium Chlorogloeopsis PCC 6912. The photoreceptor mediates at least the photosensory induction of mycosporine-like amino acid (MAA) synthesis. Because MAA synthesis in this organism can also be induced under salt stress, we could distinguish between the photosensory and the purely biochemical requirements of MAA synthesis. Neither visible light nor UV radiation was necessary for the biosynthetic process, thus indicating that the UVB (280-320 nm) dependence of biosynthesis is based on a UV photosensory capacity of the organism. An action spectrum of the MAA synthesis showed a distinct peak at 310 nm tailing down into the UVA (320-400 nm) region with no detected activity above 340 nm. We found that radiation below 300 nm caused significant inhibition of synthesis of MAAs indicating that the action spectrum at these wavelengths may not have been satisfactorily resolved. We propose that a pterin is a good candidate for a photoreceptor chromophore as (1) reduced pterins present absorption spectra congruent with the action spectrum obtained; and (2) an inhibitor of the biosynthetic pathway of pterins and an antagonist of excited states of pterins, both depressed the photosensory efficiency of induction but not its chemosensory efficiency.     

Protective effects of mycosporine-like amino acids of Synechocystis sp. PCC 6803 and their partial characterization

In this work, mycosporine-like amino acids (MAAs) of Synechocystis sp. PCC 6803 were characterized and were investigated on UV induction and protective ability. High performance liquid chromatographic (HPLC) studies revealed three major compounds in the MAAs. By UV absorption and mass spectra analysis, one of the compounds was tentatively identified as mycosporine-tau (M-tau). One novel compound similar to usujirene was tentatively named as dehydroxylusujirene, and the other novel compound was named as M-343 according to its absorption maximum. In vivo experiments indicated that M-tau was induced by both UV-A and UV-B, while dehydroxylusujirene and M-343 were only induced by UV-A, suggesting that different chromophores were involved in MAAs synthesis in Synechocystis sp. PCC 6803. It was also indicated that M-343 could be photochemically synthesized from some precursors. Under both UV and oxidation stresses, M-343 was more stable than dehydroxylusujirene and M-tau. Considering the reaction with H2O2, M-tau and dehydroxylusujirene might be potential antioxidants in reaction with physiological reactive oxygen species in vivo. In protection experiments, the MAAs exhibited efficient protective ability towards UV-B and H2O2 stresses, with maximal protection rates of 30% and 21.5%, respectively. These results indicate that the MAAs in Synechocystis sp. PCC 6803 act as both UV-screen and antioxidant.     

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.     

Adaptation strategies of the sheathed cyanobacterium Lyngbya majuscula to ultraviolet-B

Lyngbya majuscula is a dominant organism in the east coast of India forming characteristic mat in dried saline soils simultaneously exposed to solar radiation of the tropics. Studies on the growth response, changes in the spectral properties of the methanolic extract and protein profile of this estuarine sheathed cyanobacterium to UV-B revealed existence of effective adaptation mechanism to withstand prolonged UV-B radiation. Carotenoids along with MAAs of the organism was increased with increase in UV irradiation. Increase in thickness of the mucilaginous sheath layer as well as cellular carbohydrate content was observed upon exposure to prolonged UV-B dose. Induction of 21 and 33 kDa low molecular weight proteins, and a 99 kDa protein together with formation of distinct multilayered sheath embedding trichomes with granulated cells were the adaptive features of the organism to cope with UV-B stress. The organism was considerably revived after incubating the irradiated cells in mineral medium under florescent light and in the dark suggesting existence of photoreactivation and dark repair in this cyanobacterium. However more experiments are needed to establish the existence of photoreactivation and dark repair mechanism in the studied cyanobacterium.     

Monitoring of Solar Irradiance in the High Andes

Solar radiation has been measured in the high Andes near Laguna Lejia (latitude 23° 26′ 23.30" S, longitude 67° 38′ 14.29" W) at an elevation of 4715 m between December 2016 and December 2017. Irradiances were monitored in four wavelength channels: PAR (400–700 nm), UV-A (315–400 nm), UV-B (295–315 nm) and short-wavelength UV-B (295–310 nm) with a new radiometer. In addition, ambient temperatures were recorded. Record values have been found for PAR (exceeding 600 W m⁻²), UV-A (close to 95 W m⁻²), UV-B (3.13 W m⁻²) and short-wavelength UV-B (0.144 W m⁻²) during Austral spring. The winter irradiance values slightly exceeded 50% of these values. Maximal cloud effects due to multiple reflections were 45, 38, 32 and 35% higher than values under cloudless skies for PAR, UV-A, UV-B and short-wavelength UV-B, respectively. Record irradiance for this site shows a UV index reaching and exceeding 20, which is due to low solar zenith angles, the altitude, low water vapor and aerosol concentrations in the atmosphere as well as low total column ozone concentrations.     

Does Enhanced Solar UV‐B Radiation Affect Marine Primary Producers in Their Natural Habitats?

This article is a highlight of the paper by Li et al. in this issue of Photochemistry and Photobiology as well as a short summary of the research on the effects of solar UV-B radiation on primary production in the oceans. Laboratory experiments under controlled conditions using artificial light sources indicate species-specific damage of many phytoplankton groups. Mesocosm studies in enclosures of limited volume allow analyzing UV effects in multigeneration monitoring of natural assemblages. Field studies to determine the effects of short-wavelength solar radiation require sensitive instrumentation and measurements over extended areas of the open ocean to yield significant results. Results from a cruise described in the paper by Li et al. indicate clear effects of UV-B and UV-A on the photosynthetic carbon fixation of phytoplankton communities with spatial differences between coastal and open-ocean waters. Increasing temperatures and acidification in the ocean due to global climate change may exacerbate the detrimental effects of solar UV-B radiation.     

Physiological responses of Acropora cervicornis to increased solar irradiance

The effects of increased UV radiation (UV-B [280-320 nm] + UV-A [320-400 nm]; hereafter UVR) on the growth, production of photosynthetic pigments and photoprotective mycosporine-like amino acids (MAAs) were studied in the threatened Caribbean coral Acropora cervicornis transplanted from 20 to 1 m depth in La Parguera, Puerto Rico. The UVR exposure by the transplanted colonies was significantly higher than that at 20 m, while photosynthetically active radiation (PAR) only increased by 9%. Photosynthetic pigments, quantified with HPLC, as well as linear extension rates and skeletal densities, were significantly reduced 1 month after transplantation to 1 m depth, while MAAs increased significantly despite immediate paling experienced by transplanted colonies. While these colonies showed a significant reduction in photosynthetic pigments, there were no significant reductions in zooxanthellae densities suggesting photoacclimation of the coral's symbionts to the new radiation conditions. The results suggest that while corals might be able to survive sudden increases in UVR and PAR, their skeletal structure can be greatly debilitated due to a reduction in the photosynthetic capacity of their symbionts and a possible relocation of resources.     

RESPONSE DIFFERENCES BETWEEN TWO SOYBEAN CULTIVARS WITH CONTRASTING UV-B RADIATION SENSITIVITIES

Abstract— Soybeans (Glycine max [L.] Men. cvs. Essex and Williams) were grown in an unshaded greenhouse under two levels of biologically effective ultraviolet-B (UV-B_BE) radiation (effective daily dose: 0 and 11.5 kJ m^-2) for 34 days. Ultraviolet-B radiation reduced leaf area and total plant mass in Essex but these parameters were unaffected in Williams. Differences in both anatomical and biochemical characteristics were found between cultivars. Some of these differences were inherently distinct between cultivars while others were variably induced by UV treatment. Specific leaf weight. an estimate of leaf thickness, was unchanged in Essex but increased in Williams with UV-B irradiation. The relative increase in concentration of UV-absorbing compounds in leaf tissues after UV-B irradiation was greater in Williams. The composition of UV-absorbing compounds in leaf tissues differed between the two cultivars but was unaffected by UV-B radiation. Although total soluble proteins and total peroxidase activity were similar between cultivars, several electrophoretically distinct peroxidase activities were detected. Therefore, the intraspecific variation in UV-B sensitivity found in soybean appears to be correlated with a suite of anatomical and biochemical differences, including leaf thickness, composition and concentration of UV-absorbing compounds in leaf tissues, and possibly differences in peroxidase activities.