Accumulation Of Mycosporine-like Amino Acids Research Articles

Photoprotection mechanisms against ultraviolet radiation in Heterocapsa sp. (Dinophyceae) are influenced by nitrogen availability: Mycosporine‐like amino acids vs. xanthophyll cycle

The photoprotective and acclimation capacity against ultraviolet radiation (UVR) was assessed for the dinoflagellate Heterocapsa sp. We examined the effect of UVR and N availability on photosynthetic activity and on the accumulation of photoprotective substances such as mycosporine‐like amino acids (MAAs) and xanthophyll cycle pigments. Cells were cultivated under two different light treatments, photosynthetically active radiation (PAR) and PAR + UVR, and at two NaNO3 concentrations, mid nitrogen (MN, 0.1 mmol L−1) and high nitrogen (HN, 1 mmol L−1) for 6 d. MAA and photosynthetic pigment contents as well as maximum quantum yield of fluorescence (Fv : Fm) and electron transport rate were analyzed at the initial time and after 3 and 6 d of experimentation. Fv : Fm decreased because of UVR and N limitation. N enrichment reduced the deleterious effect of UVR on photosynthesis. The content of photosynthetic pigments and MAAs was higher at HN than at MN supply and a positive effect of UVR on MAA and pigment accumulation was observed, suggesting that under HN conditions the deleterious UVR effect is counteracted by MAAs. Under N limitation thermal energy dissipation takes place by the xanthophyll cycle, i.e., an increase of the de‐epoxidation degree was observed under these culture conditions. However, UVR seems to favor diadinoxanthin accumulation; thus, no photoprotection through the xanthophyll cycle seems available in cells exposed to PAR + UVR and MN. We conclude that not only MAA accumulation but also N availability is very important to determine the photoprotective capacity against UVR of Heterocapsa sp.

Accumulation of Mycosporine‐like Amino Acids in Asparagopsis armata Grown in Tanks with Fishpond Effluents of Gilthead Sea Bream, Sparus aurata

Abstract.— The accumulation of ultraviolet (UV)‐screen substances, mycosporine‐like amino acids (MAAs), in the tetrasporophytic phase of the red alga Asparagopsis armata grown in fishpond effluents of gilthead sea bream, Sparus aurata, is analyzed. Both the effects of total ammonium nitrogen (TAN) fluxes and the algal densities on MAA accumulation were investigated. MAAs increased with the TAN flux, but only until values lower than 100 μM/h. Above this flux, the MAA content decreased, whereas algal yield increased. The content of individual MAAs was related to nitrogen (N) status, that is, shinorine percentage slightly decreased and palythine increased with increasing N fluxes. The decrease of MAAs at high flux of N (up to 100 μM/h) is related to the decrease of water residence time and the decrease of the biofiltration efficiency. Under different TAN fluxes and algal densities, MAA content was negatively related to algal yield indicating that MAAs were accumulated only under a high ammonium‐N availability. Thus, an energy allocation between growth (primary metabolism) and MAA accumulation (secondary metabolism) is regulated by the absorption capacity of inorganic N. In conclusion, A. armata, in addition to its high biofiltration capacity of nutrients, is a good source of MAAs as potential UV screen photoprotectors.

Isolate-specific effects of ultraviolet radiation on photosynthesis, growth and mycosporine-like amino acids in the microbial mat-forming cyanobacterium Microcoleus chthonoplastes

Microcoleus chthonoplastes constitutes one of the dominant microorganisms in intertidal microbial mat communities. In the laboratory, the effects of repeated daily exposure to ultraviolet radiation (16:8 light:dark cycle) was investigated in unicyanobacterial cultures isolated from three different localities (Baltic Sea = WW6; North Sea = STO and Brittany = BRE). Photosynthesis and growth were measured in time series (12-15 days) while UV-absorbing mycosporine-like amino acids (MAAs) and cellular integrity were determined after 12 and 3 days exposure to three radiation treatments [PAR (22 mumol photon m(-2) s(-1)) = P; PAR + UV-A (8 W m(-2)) = PA; PAR + UV-A + UV-B (0.4 W m(-2)) = PAB]. Isolate-specific responses to UVR were observed. The proximate response to radiation stress after 1-day treatment showed that isolate WW6 was the most sensitive to UVR. However, repeated exposure to radiation stress indicated that photosynthetic efficiency (F (v)/F (m)) of WW6 acclimated to UVR. Conversely, although photosynthesis in STO exhibited lower reduction in F (v)/F (m) during the first day, the values declined over time. The BRE isolate was the most tolerant to radiation stress with the lowest reduction in F (v)/F (m )sustained over time. While photosynthetic efficiencies of different isolates were able to acclimate to UVR, growth did not. The discrepancy seems to be due to the higher cell density used for photosynthesis compared to the growth measurement. Apparently, the cell density used for photosynthesis was not high enough to offer self-shading protection because cellular damage was also observed in those filaments under UVR. Most likely, the UVR acclimation of photosynthesis reflects predominantly the performance of the surviving cells within the filaments. Different strategies were observed in MAAs synthesis. Total MAAs content in WW6 was not significantly different between all the radiation treatments. In contrast, the additional fluence of UV-A and UV-B significantly increased MAAs synthesis and accumulation in STO while only UV-B fluence significantly increased MAAs content in BRE. Regardless of the dynamic photosynthetic recovery process and potential UV-protective functions of MAAs, cellular investigation showed that UV-B significantly contributed to an increased cell mortality in single filaments. In their natural mat habitat, M. chthonoplastes benefits from closely associated cyanobacteria which are highly UVR-tolerant due to the production of the extracellular UV-sunscreen scytonemin.

Photoprotective compounds in weakly and strongly pigmented copepods and co‐occurring cladocerans

Summary1. The prevalence of mycosporine‐like amino acids (MAAs) – a group of potential ultraviolet (UV)‐photoprotective compounds – was surveyed across 11 species of freshwater copepods from 20 lakes of varying ultraviolet radiation (UVR) transparency in North America, New Zealand and Argentina. Co‐occurring cladocerans were also analysed (seven species from 12 lakes). Many of the calanoid copepod populations were red with carotenoid pigmentation, allowing comparison of MAA and carotenoid accumulation as photoprotective strategies.2. In two Pennsylvania (U.S.A.) lakes, MAA and carotenoid contents were followed during the early spring to mid‐summer period of lake warming. A pronounced seasonal pattern of higher carotenoid/low MAA content in spring, shifting to low carotenoid/higher MAA content in summer, was observed in calanoids from the more UV transparent lake.3. All copepod samples contained MAAs. Visibly red calanoids, especially southern Hemisphere Boeckella, often had moderate to high concentrations (2.5–11 μg MAA mg−1 dw), but low concentrations (0.04–1 μg MAA mg−1 dw) in some N. American red calanoids show that high carotenoid pigmentation (e.g. 5–10 μg carotenoid mg−1 dw) does not necessarily imply high MAA content.4. No cladoceran sample had more than trace amounts of MAAs (<0.05 μg mg−1 dw). Therefore, MAA accumulation does not seem to be a photoprotective strategy utilized by Daphnia (five species from nine lakes) or other cladocerans.5. Seven identifiable MAAs were widely distributed among both calanoids and cyclopoids. Shinorine was ubiquitous and was usually the most abundant MAA in N. American samples. In contrast, porphyra‐334 was the predominant MAA in the southern Hemisphere Boeckella.6. Copepods from higher UVR lakes tended to have a higher MAA content, but this relationship was statistically weak overall and taxon‐specific when found.

Sources of mycosporine‐like amino acids in planktonic Chlorella‐bearing ciliates (Ciliophora)

Mycosporine-like amino acids (MAAs) are a family of secondary metabolites known to protect organisms exposed to solar UV radiation. We tested their distribution among several planktonic ciliates bearing Chlorella isolated from an oligo-mesotrophic lake in Tyrol, Austria. In order to test the origin of these compounds, the MAAs were assessed by high performance liquid chromatography in both the ciliates and their symbiotic algae.Considering all Chlorella-bearing ciliates, we found: (i) seven different MAAs (mycosporine-glycine, palythine, asterina-330, shinorine, porphyra-334, usujirene, palythene); (ii) one to several MAAs per species and (iii) qualitative and quantitative seasonal changes in the MAAs (e.g. in Pelagodileptus trachelioides). In all species tested, concentrations of MAAs were always <1% of ciliate dry weight.Several MAAs were also identified in the Chlorella isolated from the ciliates, thus providing initial evidence for their symbiotic origin. In Uroleptus sp., however, we found evidence for a dietary source of MAAs.Our results suggest that accumulation of MAAs in Chlorella-bearing ciliates represents an additional benefit of this symbiosis and an adaptation for survival in sunlit, UV-exposed waters.

The effects of ultraviolet radiation on photosynthetic performance, growth and sunscreen compounds in aeroterrestrial biofilm algae isolated from building facades

The effects of artificial ultraviolet radiation [UVR; 8 W m(-2) ultraviolet-A (UVA), 0.4 W m(-2) ultraviolet-B (UVB)] on photosynthetic performance, growth and the capability to synthesise mycosporine-like amino acids (MAAs) was investigated in the aeroterrestrial green algae Stichococcus sp. and Chlorella luteoviridis forming biofilms on building facades, and compared with the responses of two green algae, from soil (Myrmecia incisa) and brackish water (Desmodesmus subspicatus). All species exhibited decreasing quantum efficiency (Fv/Fm) after 1-3 days exposure to UVR. After 8-12 days treatment, however, all aeroterrestrial isolates exhibited full recovery under UVA and UVA/B. In contrast, D. subspicatus showed only 80% recovery after treatment with UVB. While Stichococcus sp. and C. luteoviridis exhibited a broad tolerance in growth under all radiation conditions tested, M. incisa showed a significant decrease in growth rate after exposure to UVA and UVA/B. Similarly D. subspicatus grew with a reduced rate under UVA, but UVA/B led to full inhibition. Using HPLC, an UV-absorbing MAA (324 nm-MAA) was identified in Stichococcus sp. and C. luteoviridis. While M. incisa contained a specific 322 nm-MAA, D. subspicatus lacked any trace of such compounds. UV-exposure experiments indicated that all MAA-containing species are capable of synthesizing and accumulating these compounds, thus supporting their function as an UV-sunscreen. All data well explain the conspicuous ecological success of aeroterrestrial green algae in biofilms on facades. Biosynthesis and accumulation of MAAs under UVR seem to result in a reduced UV-sensitivity of growth and photosynthesis, which consequently may enhance survival in the environmentally harsh habitat.

Effect of light quality on the accumulation of photosynthetic pigments, proteins and mycosporine-like amino acids in the red alga Porphyra leucosticta (Bangiales, Rhodophyta)

The effect of different light qualities (white, blue, green, yellow and red light) on photosynthesis, measured as chlorophyll fluorescence, and the accumulation of photosynthetic pigments, proteins and the UV-absorbing mycosporine-like amino acids (MAAs) was studied in the red alga Porphyra leucosticta. Blue light promoted the highest accumulation of nitrogen metabolism derived compounds i.e., MAAs, phycoerythrin and proteins in previously N-starved algae after seven days culture in ammonium enriched medium. Similar results were observed in the culture under white light. In contrast, the lowest photosynthetic capacity i.e., lowest electron transport rate and lowest photosynthetic efficiency as well as the growth rate were found under blue light, while higher values were found in red and white lights. Blue light favored the accumulation of the MAAs porphyra-334, palythine and asterina-330 in P. leucosticta. However, white, green, yellow and red lights favored the accumulation of shinorine. The increase of porphyra-334, palythine and asterina-330 occurred in blue light simultaneous to a decrease in shinorine. The accumulation of MAAs and other nitrogenous compounds in P. leucosticta under blue light could not be attributed to photosynthesis and the action of a non-photosynthetic blue light photoreceptor is suggested. A non-photosynthetic photoreceptor could be also involved in the MAAs interconversion pathways in P. leucosticta.

Effects of starvation, ammonium concentration, and photosynthesis on the UV-dependent accumulation of mycosporine-like amino acids (MAAs) in the coral Stylophora pistillata

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 295:135-156 (2005) - doi:10.3354/meps295135 Effects of starvation, ammonium concentration, and photosynthesis on the UV-dependent accumulation of mycosporine-like amino acids (MAAs) in the coral Stylophora pistillata J. Malcolm Shick1,*, Christine Ferrier-Pagès2, Renaud Grover2, Denis Allemand2,3 1School of Marine Sciences, University of Maine, 5751 Murray Hall, Orono, Maine 04469-5751, USA2Centre Scientifique de Monaco, Avenue Saint-Martin, 98000 Monaco, Principality of Monaco3UMR 1112 INRA-UNSA, University of Nice-Sophia Antipolis, Parc Valrose, BP 71, 06108 Nice Cedex 2, France *Email: shick@maine.edu ABSTRACT: This study addresses several unresolved questions regarding the biosynthesis, metabolism, regulation, and diversity of MAAs in zooxanthellate scleractinian corals. Starved colonies of Stylophora pistillata accumulated the same concentrations of mycosporine-like amino acids (MAAs) as fed corals after 28 d of exposure to photosynthetically available radiation (PAR) and ultraviolet radiation (UVR), suggesting that dietary MAAs are of little quantitative importance in this phototrophic symbiosis. Starved corals continued to accumulate MAAs and conserved them disproportionally compared with declining protein and chlorophyll a, indicating the priority placed on maintaining this UV-sunscreen defense. In 2 different colonies (SP1 and SP2) exposed to enriched (10 µM) ammonium and PAR + UVR during starvation, the final concentrations of MAAs and chlorophyll a were identical. However, under ambient ammonium (<0.4 µM), SP2 produced MAAs at the expense of chlorophyll a, whereas SP1 maintained chlorophyll a levels but synthesized less MAA. Ammonium consistently affected only the accumulation of primary, Symbiodinium-MAAs (mycosporine glycine, shinorine, porphyra-334, and mycosporine-2 glycine) and not secondary MAAs derived from the former, probably in the host’s tissues. Mycosporine-2 glycine and palythine (a secondary MAA) were synthesized by SP1 but not SP2, suggesting (1) genotypic differences between the zooxanthellae in SP1 and SP2, and (2) a biosynthetic relationship between these 2 MAAs that we proposed previously. Exposure to UVR alone did not support large-scale biosynthesis of MAAs in S. pistillata, and accumulation of the full suite of MAAs required PAR + UVR; together with an inhibitory effect of DCMU, this indicates that photosynthesis is required for the UV-stimulated, de novo biosynthesis of MAAs. Cultures of zooxanthellae isolated from S. pistillata and exposed to PAR + UVR showed increased levels of shinorine, and some production of mycosporine-glycine. Host extract had no qualitative effect on the MAAs produced by these zooxanthellae. KEY WORDS: Mycosporine-like amino acids (MAAs) · Coral · Zooxanthellae · Ultraviolet radiation (UVR) · Dissolved ammonium · Photosynthesis Full text in pdf format PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 295. Online publication date: June 23, 2005 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2005 Inter-Research.

Availability of ammonium influences photosynthesis and the accumulation of mycosporine-like amino acids in two Porphyra species (Bangiales, Rhodophyta)

The effect of ammonium concentration on photosynthetic activity estimated as in vivo chlorophyll fluorescence, i.e. maximal quantum yield (Fv/Fm) and electron transport rate (ETR) and on the accumulation of mycosporine-like amino acids (MAAs), chlorophyll a (chl a), biliproteins (BP) and soluble proteins (SP) in the red algae Porphyra leucosticta Thuret in Le Jolis collected from Lagos (Malaga, Spain) and Porphyra umbilicalis (Linnaeus) J. Agardh from Helgoland (Germany) was evaluated. Discs of both species were incubated with three ammonium concentrations (0, 100 and 300 µM) under artificial PAR and UV radiation for 7 days. Photosynthetic activity decreased under the culture conditions due to UV radiation and ammonium availability. The decrease of both Fv/Fm and maximal ETR was related to ammonium supply, i.e. the lowest decrease occurred in algae growing with the highest concentration of ammonium. In both species, after 7 days of culture, the content of chl a, BP and SP was higher under 300 µM than that under 0 and 100 µM ammonium. In both species, the content of MAAs was increased under 300 µM ammonium compared to the initial value, whereas a decrease under 0 and 100 µM ammonium was observed only in P. leucosticta. The content of MAAs in P. umbilicalis did not present significant differences compared to the initial value, probably because of the high initial content of MAAs. In both Porphyra species, four MAAs were identified: shinorine, porphyra-334, palythine and asterina-330. However, P. leucosticta modified its MAA pattern during the incubation time, reaching the same percentages found for P. umbilicalis, which did not show any change during the experimental period. P. leucosticta exhibited a decrease in BP/SP and BP/chl a ratios through the incubation time and an increase in MAAs/BP. The ratio MAAs/chl a did not show any variation with time or treatment, as was also true for all ratios in P. umbilicalis. In summary, ammonium supply diminished the decrease of Fv/Fm, increased the content of photosynthetic pigments (chlorophyll and biliprotein) and soluble protein, and stimulated of the accumulation of MAAs in the red algae P. leucosticta and P. umbilicalis.

The continuity and intensity of ultraviolet irradiation affect the kinetics of biosynthesis, accumulation, and conversion of mycosporine‐like amino acids (MAAs) in the coral Stylophora pistillata

Colonies of Stylophora pistillata unexposed to ultraviolet radiation (UVR) in laboratory aquaria contained minimal amounts of mycosporine‐like amino acids (MAAs). The concentration of MAAs increased rapidly during exposure to broadband UVR, then stabilized between 14 and 28 d of exposure. The four MAAs known to be produced by diverse zooxanthellae (Symbiodinium spp.) in culture were the first to increase in coral colonies, followed by six additional MAAs. Decreases in these four primary MAAs between days 14 and 28 were balanced by stoichiometric increases in the six secondary MAAs, suggesting a precursor‐product relationship. Discontinuing UV exposure caused rapid declines in the concentrations of primary MAAs, while secondary MAAs continued to increase, likely a manifestation of different rates of turnover of the putative enzymes involved in the de novo biosynthesis of primary MAAs and their conversion to secondary MAAs. The continued production of certain MAAs after UV exposure ceased indicates that UV is not required catalytically but is a signal that induces the enzymes of the biosynthetic pathway. Biochemically inhibiting the biosynthesis of primary MAAs after a pool of these MAAs had accumulated did not affect their conversion to secondary MAAs. Doubling the UV irradiance increased the rate of accumulation, first, of primary MAAs and, later, of secondary MAAs. Under normal UV irradiance, the eventual decline in the accumulation rate of primary MAAs was quantitatively explained by their conversion to secondary MAAs. Under doubled UV irradiance, where MAA concentrations were higher, the deceleration of accumulation of primary MAAs was twice as great as the acceleration in secondary MAAs, suggesting a regulation of the de novo biosynthesis of MAAs, perhaps by their own progressive, concentration‐dependent attenuation of UVR.

Effects of short-term irradiation on photoinhibition and accumulation of mycosporine-like amino acids in sun and shade species of the red algal genus Porphyra

The effect of irradiance (40 and 840 μmol photons m −2 s −1) of short-term (48 h) irradiation on photosynthetic activity (estimated as oxygen evolution and as chlorophyll fluorescence), specific absorption and fluorescence excitation spectra, photosynthetic pigment accumulation (chlorophyll a and biliproteins) and UV-absorbing compounds (mycosporine-like amino acids, MAAs) was investigated in sun and shade species of the red algal genus Porphyra collected in Trondheimsfjord (Norway). In the sun type, high irradiance exposure (840 μmol photons m −2 s −1) did not alter the Chl a concentration, however, exposure to a lower irradiance (40 μmol photons m −2 s −1) for 48 h significantly increased the chlorophyll concentration. The content of MAAs was significantly higher in the suntype than in the shade type algae. Porphyra-334 is the main MAA in this species followed by shinorine. The total content of MAAs significantly ( P<0.05) increased in the sun type after 48 h exposure to both high and low irradiances. However, in the shade type, porphyra-334 significantly decreased ( P<0.05) after both high and low irradiance exposure. Photosynthetic activity (as oxygen evolution) and the optimal quantum yield ( F v/ F m), as an indicator of photoinhibition, decreased under low and high irradiance in the shade type algae and no full recovery was observed when the algae were transferred to very low irradiation.The sun type algae presented a higher capacity of acclimation to increased irradiance than the shade type algae. This high acclimation of sun type algae to short term high irradiance exposure (48 h) is explained by the higher thermal dissipation. This was estimated as the ratio of nonphotochemical quenching related to the light dose ( q N:dose) and by the accumulation of MAAs.

Induction of sunscreen compounds in Antarctic macroalgae by different radiation conditions

The formation of UV-absorbing mycosporine-like amino acids (MAAs) as a photoprotective strategy against biologically harmful ultraviolet radiation was studied in Antarctic red macroalgae. After exposure to three different radiation treatments (PAR: 400–700 nm, PAR+UVA: 320–700 nm, PAR+UVA+UVB: 295–700 nm), using artificial irradiance sources under controlled conditions, the physiological capability to stimulate MAA synthesis was investigated. While 8 out of 18 species showed an induction of MAA formation and accumulation, the remaining ten, mainly deep water species, did not exhibit any traces of MAAs. The MAA-containing samples were divided into three physiological response types based on their MAA accumulation versus different radiation treatments. The first response type included Kallymenia antarctica, Gymnogongrus antarcticus, Palmaria decipiens and Porphyra plocamiestris, and exhibited additionally increasing MAA concentrations under the different radiation treatments, i.e. highest total MAA values were measured under the full radiation spectrum. The second response type included Porphyra endiviifolium and Gymnogongrus turquetii, showing highest MAA concentrations already under PAR+UVA. In contrast, Neuroglossum ligulatum and Plocamium cartilagineum exhibited a strong MAA decrease under PAR+UVR and were grouped in the third response type. No consistent MAA induction patterns could be found, even for individual MAAs, indicating that induction, formation and accumulation of individual MAAs is a very flexible and species-specific mechanism.

Ultraviolet damage and counteracting mechanisms in the freshwater copepod Boeckella poppei from the Antarctic Peninsula

The process of ozone depletion over the Antarctic continent has resulted in the increase of incident ultraviolet‐B (UVB) radiation, whose effects may be damaging to living organisms. To counteract the negative effects of ultraviolet radiation (UVR), aquatic organisms may display one or more strategies: (1) avoidance (i.e. deep distribution); (2) photoprotection through the use of “sunscreen” compounds, such as mycosporine‐like amino acids (MAAs); and (3) enzymatic repair of the damage. The effects of UVR were assessed on four populations of the copepod Boeckella poppei from Antarctic lakes using laboratory and field experiments. The results were related to measurements of DNA enzymatic repair activity and MAA concentration. This is the first study that combines these measurements in zooplankton. Boeckella poppei was highly tolerant to UVR (LD50 = 2.2–2.78 J cm−2). However, measurements of photorecovery (comparison of UVB mortality in the presence and absence of photoreactivating light) and dosage of photolyase activity indicated low rates of enzymatic repair, which may be the result of low temperatures typical of Antarctic lakes. Three different MAAs were identified, both in phytoplankton and copepods: porphyra‐334, mycosporine‐glycine, and shinorine. The population of B. poppei from Lake Boeckella had the lowest MAA concentration, as well as the lowest tolerance to artificial and natural UVR. These findings support the idea that UV tolerance in this species is related to the accumulation of MAAs. A comparison of the strategies used to cope with potentially damaging levels of UVR by different species of Boeckella indicates a high degree of plasticity in this genus, which has probably been key for its success to colonize a wide range of UV environments.

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.

Effect of high visible and UV irradiance on subtidal Chondrus crispus: stress, photoinhibition and protective mechanisms

Stress and the mechanisms of protection under excessive photosynthetically active (PAR) and ultraviolet radiation (UVR) were examined in the red alga Chondrus crispus Stackh. collected from the subtidal zone (6 m depth) at Helgoland, North Sea, Germany. Three PAR (400–700 nm) treatments without UVR and three UVR-A/B (290–400 nm) treatments supplemented with 30 μmol m −2 s −1 PAR were given twice. All three stages of plant stress, irritation, damage and acclimation, were observed under high light conditions. In the earlier stages of photoinhibitory PAR and UVR treatment, an induction phase occurred. It was characterized by a significant increase in chlorophyll a and carotenoids. The capacity to cope with high light stress in C. crispus increased with increasing duration of the induction phase. Prolonged exposures to high irradiance induced a substantial decline in the potential quantum yield of photosynthesis ( F v/ F m) and progressive pigment destruction that may be responsible for the damage stage of stress. In plants exposed to elevated PAR (3600 μmol m −2 s −1) and UVR (57.3 and 3.6 W m −2 of UVRA and UVRB, respectively), photoinhibition of F v/ F m exceeded 95% of control. Even after 20 h in low irradiance it was similar to values measured immediately after stress, indicating severe photodamage. The 1800 μmol m −2 s −1 PAR treatment also decreased the pigment content and F v/ F m, although damage was not permanent and the tissue gradually recovered. In contrast, naturally high doses of UVR (37.7 and 2.3 W m −2 of UVRA and UVRB, respectively) resulted in less photoinhibition of photosynthesis with rapid recovery of F v/ F m and pigment content, indicating the dynamic nature of photosynthetic acclimation to growth irradiance. Thus, photoinhibitory PAR damage and its repair predominate in subtidal C. crispus during the process of acclimation to a full-sun environment. Comparison between the acclimation conditions suggests that fluorescence quenching is related to the concentration of carotenoids. The increase in concentration, not only in the first but also after repeated exposures to PAR and UVR, was attributed to a protection of the photosynthetic apparatus. Additionally, accumulation of mycosporine-like amino acids (MAAs), mainly during the repeated exposures to UVR, led to substantially less inhibition of photosynthesis than expected given the practically double UVR dose. This suggests incomplete protection of C. crispus by MAAs during UVR shock. Thus, these experiments indicate that a few basic physiological strategies seem to be active during acclimation to high solar irradiance: a prolonged induction phase, dynamic photoinhibition, increased concentration of carotenoids, and accumulation of MAAs, UV-screening substances.

Selective accumulation of mycosporine-like amino acids in ovaries of the green sea urchin Strongylocentrotus droebachiensis is not affected by ultraviolet radiation

Field sampling and laboratory experiments examined whether ultraviolet radiation (UVR) affects the reproduction or the accumulation of mycosporine-like amino acids (MAAs) and ascorbic acid in ovaries of the green sea urchin Strongylocentrotus droebachiensis (Muller). Ovaries of sea urchins sampled across a depth gradient (0.5–10 m) in March 1998 did not differ in their gonadal index, or in concentrations of MAAs, or ascorbic acid. Concentrations of MAAs and ascorbic acid in ovaries were higher in sea urchins collected from a kelp bed compared with those collected from a community of crustose coralline algae. The concentrations of MAAs in ovaries varied seasonally, peaking in March, when sea urchins had high gonadal indices just before spawning. Ovaries of sea urchins maintained on controlled diets from October 1997 to April 1998 accumulated significantly higher concentrations of MAAs when fed a diet rich in MAAs than did ovaries of sea urchins fed an alga lacking MAAs, but the gonadal indices did not differ between diets. Sea urchins accumulated principally one MAA, shinorine, but not others that were available in high concentrations in their diet. Neither the gonadal index nor the ovarian concentrations of MAAs were affected by daily exposure of adult urchins to UVR for 6 months. Concentrations of ascorbic acid in ovaries did not differ among diets or UV-treatments. The percentages of nutritive phagocytes and gametic cells were not affected by diet or UVR, and did not co-vary with concentrations of MAAs or ascorbic acid in ovaries. These data support previous demonstrations that female sea urchins accumulate MAAs from their diet of macroalgae, but further show that the accumulation is selective for specific MAAs, particularly shinorine, and that adult S. droebachiensis do not accumulate MAAs in their ovaries or eggs in response to UV-exposure. These are also the first experimental studies to address whether MAAs are affected by or regulate gametogenesis, and indicate that they do not.

Factors Controlling the Formation of UV-absorbing Mycosporine-like Amino Acids in the Marine Red Alga Palmaria palmata from Spitsbergen (Norway)

Summary The effects of various filtered natural radiation conditions (solar without UVA+B, solar without UV B, solar) on the contents of UV-absorbing mycosporine-like amino acids (WAS) in the marine red alga Palmaria palmata have been investigated in the Arctic Kongsflord (Spitsbergen, Norway) over the summer 1997. Eight different UV-absorbing mycosporine-like amino acids (MAAs) were detected in this alga, seven of which could be identified, namely mycosporine-glycine, shinorine, porphyra-334, palythine, asterina-330, palythinol and palythene. The remaining substance exhibited an absorption maximum at 357 nm, but could not be identified. The specific amount of MAAs decreased with increasing collecting depth. Transplantation of P. palmata from 3 m depth to near surface water (0.2 m) followed by 1 week exposure to the various radiation treatments stimulated the accumulation of MAAs. All treatments led to a strong increase in total MAAs, but individual compounds showed different responses under the three spectral wavebands. While exposure to natural solar radiation without UVA+B was accompanied with a 6-fold increase in the porphyra-334 concentration, treatment without UV -13 gave similar results plus an accumulation of shinorine. Under the full solar spectrum P. palmata showed the accumulation of three MAAs, porphyra-334 and shinorine, and additionally that of palythine. These data indicate a wavelengthspecific stimulation of the formation of different MAAs, as well as the strongest accumulation of total MAAs under the full solar spectrum. In another experiment P. palmata was collected from 7.5 m depth, transplanted to 1 m and exposed for 9 days to solar radiation without UV A+B, solar radiation without UV -13 and the full solar spectrum to follow the kinetics of MAA accumulation. All radiation treatments led to an accumulation of total MAA contents over time with the full solar spectrum being the most effective. However, in contrast to P. palmata transplanted from 3 m depth, plants from 7.5 m showed a different response in the MAA accumulation pattern. In the latter samples palythine was always the quantitatively dominant MAA and exhibited also the strongest increase after transplantation to shallow waters under all radiation treatments. Finally, a microscale variation in the MAA concentrations along the algal thalli was measured. Older self-shaded basal parts of P. palmata exhibited much lower NM amounts than young apical tips. All data well support the suggested physiological function of MAAs as natural UV-sunscreens.

The occurrence of UV-B absorbing mycosporine-like amino acids in freshwater and terrestrial microalgae (Chlorophyta)

The occurrence of mycosporine-like amino acids (MAAs) in freshwater and terrestrial microalgae and their accumulation in response to UV-B exposure were examined. Three UV-B-resistant species, Enallax coelastroides, Scenedesmus sp. and Scotiella chlorelloidea, and four UV-B-sensitive microalgal species: Ankistrodesmus spiralis, Chlorella minutissima, Chlorella sorokiniana and Pseudococcomyxa sp. were found to contain MAAs. However, Coelastrum microporum did not appear to contain any MAA. A total of seven MAAs was identified among the tested species. Besides five known MAAs: mycosporine-Gly ( λ max = 310 nm), palythine ( λ max = 320 nm), asterina ( λ max = 330 nm), shinorine ( λ max = 334 nm) and porphyra ( λ max = 334 nm), two novel compounds (compound I: λ max = 302 nm, Rt = 2.6 min; compound II: λ max = 292 nm, Rt = 7.3 min) were found in Ch. sorokiniana and Scenedesmus sp. The accumulation of MAAs was induced by both artificial and solar UV-B radiation, which was observed in both the UV-B-resistant and UV-B-sensitive species. No clear correlation between MAA accumulation and UV-B resistance of the photosynthetic apparatus was established. The response of MAA accumulation to UV-B exposure was species-dependent and individual MAA-specific.

The effect of ultraviolet radiation on photosynthesis and ultraviolet‐absorbing substances in the endemic Arctic macroalga Devaleraea ramentacea (Rhodophyta)

In field studies conducted at the Kongsfjord (Spitsbergen), the effect of filtered natural radiation conditions (solar without ulraviolet [UV]‐A+UV‐B, solar without UV‐B, solar) on photosynthesis and the metabolism of UV‐absorbing mycosporine‐like amino acids (MAAs) in the marine red alga Devaleraea ramentacea have been studied. While solar treatment without UV‐A+UV‐B did not affect photosynthesis during the course of a day, solar without UV‐B and the full solar spectrum led to a strong inhibition. However, after offset of the various radiation conditions, all algae fully recovered. Isolates collected from different depths were exposed in the laboratory to artificial fluence rates of photosynthetic active radiation (PAR), PAR+UV‐A, and PAR+UV‐A+UV‐B. The photosynthetic capacity was affected in accordance with the original sampling depth, i.e. shallow‐water isolates were more resistant than algae from deeper waters, indicating that D. ramentacea is able to acclimate to changes in irradiance. Seven different UV‐absorbing MAAs were detected in this alga, namely mycosporine‐glycine, shinorine, porphyra‐334, palythine, asterina‐330, palythinol, and palythene. The total amount of MAAs continuously decreased with increasing collecting depth when sampled in mid June, and algae taken in late August from the same depths contained on average 30–45% higher MAA concentrations, indicating a seasonal effect as well. The presence of increasing MAA contents with decreasing depth correlated with a more insensitive photosynthetic capacity under both UV‐A and UV‐B treatments. Populations of D. ramentacea collected from 1 m depth, with one fully exposed to solar radiation and the other growing protected as understorey vegetation underneath the kelp Laminaria saccharina, exhibited quantitatively different MAA compositions in the apices. The exposed seaweeds contained 2.5‐fold higher MAA values compared with the more shaded algae. Moreover, the exposed isolates showed a strong tissue gradient in MAAs, pigments, and proteins. The green apices contained 5‐fold higher MAA contents than the red bases. Transplantation of D. ramentacea from 2 m depth to the surface induced the formation and accumulation of MAAs after 1 week exposure to the full solar spectrum. Control samples which were treated with the solar spectrum without UV‐A+B or with solar without UV‐B showed unchanged MAA contents, indicating a strong UV‐B effect on MAA metabolism. All data well supported the suggested physiological function of MAAs as natural UV sunscreens in macroalgae.

Photoinduction of UV-absorbing compounds in Antarctic diatoms and Phaeocystis antarctica

The presence of UV-absorbing compounds, thelr In vivo absorption and photoinducibility were investigated in the colonial form of the prymnesiophyte Phaeocystis antarctica and 11 species of Antarctic diatoms. High in vivo phytoplankton absorption peaks centered at 315-320 nm wavelengths indicated the presence of UV-absorbing compounds in all cultures of P. antarctica examined. UVabsorbing compounds, detected as in vivo absorption peaks at slightly longer wavelengths (330-333 nm), were present in most diatom species, but were absent or present in minute amounts in smaller species. UV-absorbing compounds were identified in the diatoms as the mycosporine-like amino acids (MAAs) porphyra-334, mycosporine-glycine, and shinorine but could not be positively identified in P. antarctica. Accumulation of MAAs was induced by llght in the blue/UV portion of the spectrum (305-460 nm). For diatoms, induction was most effective at wavelengths between 370 and 460 nm with very little response observed at ultraviolet-B (UVB, 280-320 nm) wavelengths. In contrast, induction was maximal at 340 nrn and significant at wavelengths down to 305 nrn in colonies of P. antarctica. Induction requlred continuous illurn~nation and exhibited an Initial lag phase (10 to 24 h in length), an exponential phase (60 to 120 h in length), and a steady-state phase. The cellular content of MAAs was stable in viable cells kept for over 2 mo In prolonged darkness and became d~luted through successive cell divisions in cells grown in non-inducing ~llumination (red and yellow light). The potential sunscreening effect (S) of MAAs, calculated as the fractional reduction of UV exposure to a centrally-located cellular target, ranged from 0.03 to 0.50 for diatom cells and from 0.65 and 0.72 for P, antarctica colonies. S exhibited an increasing trend with cell and colony size. Whereas MAAs are thought to be intracellularly located, the large values of S determined for P. antarctica suggests that UV-absorbing compounds associated with the colonies are located within the extracellular colonial matrix. The results indicate that most phytoplankton species examined have the potential to respond to an increase in UVR resulting from seasonal changes in solar zenith angle by increasing their MAA content. A similar response to elevated UVB levels resulting from depleted ozone concentrations may be limited to P. antarctica.