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 micromol 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 micromol photons m(-2) s(-1)) did not alter the Chl a concentration, however, exposure to a lower irradiance (40 micromol 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.     

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 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 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.     

Photodegradation and photosensitization of mycosporine-like amino acids

The photodegradation and photosensitization of several mycosporine-like amino acids (MAAs) were investigated. The photodegradation of the MAA, palythine, was tested with three photosensitizers: riboflavin, rose bengal and natural seawater. For comparison of degradation rates, the riboflavin-mediated photosensitization of six other MAAs was also examined. When riboflavin was used as a photosensitizer in distilled water, MAAs were undetectable after 1.5h. Palythine showed little photodegradation when rose bengal was added as the photosensitizer (k=0.12x10(-3)m(2)kJ(-1)). Palythine dissolved in natural seawater containing high nitrate concentrations also showed slow photodegradation rate constants (k=0.26x10(-3)m(2)kJ(-1)) over a 24-h period of constant irradiation. Similar experiments in deep seawater with porphyra-334 and shinorine resulted in 75% of the initial MAA remaining after 4h of irradiation and rates of 0.018 and 0.026x10(-3) m(2) kJ(-1), respectively. Experiments conducted in deep seawater with riboflavin additions resulted in photodegradation rate constants between 0.77x10(-3) and 1.19x10(-3)m(2)kJ(-1) for shinorine and porphyra-334, respectively. Photoproduct formation appeared to be minimal with the presence of a dehydration product of the cycloheximine ring structure indicated as well as the presence of amino acids. Evidence continues to build for the role of MAAs as potent and stable UV absorbers. This study further highlights the photostability of several MAAs in both distilled and seawater in the presence of photosensitizers.     

Occurrence of Mycosporine-like Amino Acids (MAAs) from the Bloom-Forming Cyanobacteria Aphanizomenon Strains

Mycosporine-like amino acids (MAAs) are widespread in various microbes and protect them against harsh environments. Here, four different Aphanizomenon species were isolated from severely eutrophic waterbodies, Lake Dianchi and the Guanqiao fishpond. Morphological characters and molecular phylogenetic analysis verified that the CHAB5919, 5921, and 5926 strains belonged to the Aphanizomenon flos-aquae clade while Guanqiao01 belonged to the Aphanizomenon gracile clade. Full wavelength scanning proved that there was obvious maximal absorption at 334 nm through purified methanol extraction, and these substances were further analyzed by HPLC and UPLC-MS-MS. The results showed that two kinds of MAAs were discovered in the cultured Aphanizomenon strains. One molecular weight was 333.28 and the other was 347.25, and the daughter fragment patterns were in accordance with the previously articles reported shinorine and porphyra-334 ion characters. The concentration of the MAAs was calibrated from semi-prepared MAAs standards from dry cells of Microcystis aeruginosa PCC7806 algal powder, and the purity of shinorine and porphyra-334 were 90.2% and 85.4%, respectively. The average concentrations of shinorine and porphyra-334 were 0.307–0.385 µg/mg and 0.111–0.136 µg/mg in Aphanizomenon flos-aquae species, respectively. And there was only one kind of MAAs (shinorine) in Aphanizomenon gracile species.,with a content of 0.003–0.049 µg/mg dry weight among all Aphanizomenon gracile strains. The shinorine concentration in Aphanizomenon flos-aquae was higher than that in Aphanizomenon gracile strains. The total MAAs production can be ranked as Aphanizomenon flos-aquae > Aphanizomenon gracile.     

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.     

Can Mycosporine‐Like Amino Acids Act as Multifunctional Compounds in Gymnodinium catenatum (Dinophyceae)?

MAAs originating from Gymnodinium catenatum were subjected to H₂O₂ oxidation, light and heat. Shinorine and porphyra‐334 were the more resistant to all treatments, mycosporine‐glycine (MYGL) was the least resistant to oxidation and heat, whereas palythene and M‐370 were the least resistant to light. MYGL and M‐311 were similarly resistant to photodegradation and oxidation in the dark and low temperature, but M‐311 was more resistant to oxidation under light or heat. The ratio M‐370/M‐365 changed from 29:1 to 6:1 ratio after 240 h of exposure to fluorescent light, indicating that M‐365 could represent the M‐370 cis‐isomer. The role of MAAs as antioxidants and/or osmolytes was evaluated by studying effects of abrupt salinity reduction. Both increases or decreases in concentrations were observed and were dependent on the MAA initial concentration and its chemical structure. The relative increase in MAAs with a known antioxidant capacity (MYGL, palythene) followed an exponential decay trend related to initial concentration. The relative decrease in highly polar MAAs (shinorine, porphyra‐334, M‐332) with a suspected osmolyte role followed a rise to a maximum with the increase in initial concentration. Whether or not MAAs play a significant role in osmoregulation, their loss can occur upon hypoosmotic shock.     

Effects of Light and Salinity Stresses in Production of Mycosporine‐Like Amino Acids by Gymnodinium catenatum (Dinophyceae)

Mycosporine‐like amino acids (MAAs) were analyzed in a Portuguese Gymnodinium catenatum strain when transferred to high salinity and high light conditions. Total MAA concentrations increased progressively between 30 and 36 psu, attaining at 36 psu 2.9‐fold the 30 psu treatment. When abruptly transferred to solar light in an outdoor shadowed location, MAA concentration increased steadily along the day for most compounds. After 8 h, mycosporine–glycine, palythene and M‐319 attained or surpassed 25‐fold their initial concentration, while M‐370 only attained 4‐fold concentration. When transferred from halogen to fluorescent light, polar MAAs such as shinorine and porphyra‐334, increased until day two and then declined, while M‐370 increase slowly, becoming the dominant compound from the profile after 1 week. These experiments put into evidence the relation of palythene with M‐319, which was further identified as its acid degradation product, palythine. Acid degradation of M‐370 originated M‐324, while M‐311 seems to be the precursor of M‐370. Under high salinity and high light conditions chain formation was altered toward shorter chains or solitary cells. This alteration can represent a morphological stress sign, which in the natural environment could affect average population speed during daily vertical migrations.     

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.     

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.     

Electrospray ionization tandem mass spectrometric and electron impact mass spectrometric characterization of mycosporine-like amino acids

Positive-ion mass spectral fragmentations of seven mycosporine-like amino acids (MAAs) are reported and discussed. The MAAs studied are small compounds composed of a cycloheximine ring substituted with amino acid or amino alcohol units. Techniques used include electron impact (EI) and electrospray ionization (ESI) with tandem mass spectrometry (MS/MS). ESI-MS/MS showed unusual small radical losses, generally resulting from the loss of a methyl group with the exception of shinorine and porphyra for which the initial losses were 30 and 44 Da, respectively. As expected from structural similarities, porphyra, shinorine and palythinol displayed similar fragmentation patterns, while palythenic acid and palythene fragmented in a similar manner. Overall, the ESI-MS/MS fragmentations at m/z <200 exhibited a distinctive pattern for all seven MAAs with characteristic ions at m/z 137, 168, 186, and 197 or 199. Several ions were observed for each of the MAAs analyzed, and together provide a useful and potentially diagnostic pattern for identification of MAAs and as an aid in structure elucidation of novel MAAs. For GC/EI-MS analysis, trimethylsilyl (TMS) derivatives were made. The EI-MS fragmentation patterns of TMS-MAAs showed many features typical of TMS-derivatized alpha-amines. The precursor TMS-MAA ion was not detected, but a [M-90](+ radical) ion was the highest-mass intense peak observed for palythine, palythinol and shinorine, while palythene gave a [M-116](+ radical) ion. Besides determining the number of acidic hydrogens, EI-MS of TMS-derivatized MAAs will aid in structure elucidation of novel MAAs.     

Effects of nitrogen source and UV radiation on the growth, chlorophyll fluorescence and fatty acid composition of Phaeodactylum tricornutum and Chaetoceros muelleri (Bacillariophyceae)

Cultures of the marine diatoms Phaeodactylum tricornutum and Chaetoceros muelleri were grown in f/2 medium supplied with either nitrate (N-Nt), ammonium (N-Am) or urea (N-Ur) as the nitrogen (N) source at the same final N concentration (0.88 mM). Exponential growth phase cultures of the two diatoms were exposed to four different light regimes for 2 days: (UVAR) PAR (60 micromol quanta m-2 s-1) plus 8.22 W m-2 (unweighted) UVAR; (high UVBR) PAR (60 micromol quanta m-2 s-1) plus 1.04 W m-2 (unweighted) UVBR plus 13.73 W m-2 (unweighted) UVAR; (low UVBR) PAR (60 micromol quanta m-2 s-1) plus 0.19 W m-2 (unweighted) UVBR plus 2.76 W m-2 (unweighted) UVAR and (PAR) PAR (60 micromol quanta m-2 s-1) alone (control). No significant effects of N source on the growth rates of the two diatoms were detected. The maximum effective quantum yield of PSII, PhiPSIIe-max, and the initial slope of the light curve, alpha, of P. tricornutum and C. muelleri were all inhibited, whereas Ik was somewhat increased, as a consequence of 2 days of exposure to all the UVR treatments. Multiple factor ANOVA revealed that all the major fatty acids, both in P. tricornutum and C. muelleri, were influenced more strongly by N source than by UVR. The composition of saturated fatty acids (SFA), monounsaturated fatty acids (MUFA) and polyunsaturated fatty acids (PUFA) in P. tricornutum and C. muelleri exhibited almost the same pattern of variation with N source and UVR. The maximum value of SFA was found in the N-Am treatment, that of MUFA in the N-Nt treatment and for PUFA in the N-Ur treatment irrespective of the UV radiation. On the other hand, the impact of UVR resulted in an increase of PUFA and a reduction of SFA both in P. tricornutum and C. muelleri under all N sources.     

Palythine–threonine,a major novel mycosporine-like amino acid (MAA) isolated from the hermatypic coral Pocillopora capitata

Using a high-resolution reverse-phase liquid chromatography method we found that the tissues of the hermatypic coral Pocillopora capitata (collected in Santiago Bay, Mexico) contain a high diversity of primary and secondary mycosporine-like amino acids (MAAs) typical of some reef-building coral species: mycosporine–glycine, shinorine, porphyra-334, mycosporine–methylamine–serine, mycosporine–methylamine–threonine, palythine–serine, palythine and one additional novel predominant MAA, with an absorbance maximum of 320 nm. Here we document the isolation and characterization of this novel MAA from the coral P. capitata. Using low multi-stage mass analyses of deuterated and non deuterated compounds, high-resolution mass analyses (Time of Flight, TOF) and other techniques, this novel compound was characterized as palythine–threonine. Palythine–threonine was also present in high concentrations in the corals Pocillopora eydouxi and Stylophora pistillata indicating a wider distribution of this MAA among reef-building corals. From structural considerations we suggest that palythine–threonine is formed by decarboxylation of porphyra-334 followed by demethylation of mycosporine–methylamine–threonine.     

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.     

Daily variation in cellular content of UV-absorbing compounds mycosporine-like amino acids in the marine dinoflagellate Scrippsiella sweeneyae

Sudden exposure experiments to high PAR (photosynthetically available radiation) or high PAR+UVR (ultraviolet radiation) were conducted for the marine dinoflagellate Scrippsiella sweeneyae acclimated to either low PAR or high PAR to determine the induction of cellular mycosporine-like amino acid (MAA) in relation to photosynthesis status. When the exposure to high PAR (30.8 Wm(-2)) was provided at different time in the light period for S. sweeneyae acclimated to low PAR (7.7 Wm(-2)) which suppressed photosynthesis, S. sweeneyae could enhance the induction of MAA but it only occurred in the first half of the light period. When UVR exposure was provided for the culture acclimated to high PAR which enhanced photosynthesis, cellular MAA content did not increase during the entire light period, but displayed daily variation similar to the control for two and half days. Daily variation of cellular MAA content did not synchronized with that of cell volume and cellular chlorophyll a content. The individual MAAs also revealed similar daily variations with different phase, which increased for a few hours in the beginning of the light period, except for cellular palythine content. Thus the total cellular MAA content revealed daily variation with changing the relative composition within a few hours. As one of the biological protective strategies against harmful UVR in sunlight, the daily vertical migration in the bloom forming dinoflagellates might be accompanied by the daily variation of cellular MAA content for a photosynthesis at daytime.     

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.     

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.     

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.     

In vitro cis-trans photoisomerization of palythene and usujirene. Implications on the in vivo transformation of mycosporine-like amino acids

The in vitro photoinduced reactions of the mycosporine-like amino acids (MAA) usujirene and palythene were studied by monochromatic stationary irradiation at 366 nm. High-performance liquid chromatography analysis of the irradiated aqueous solution of usujirene indicated a low photoreactivity on the basis of the observed photodecomposition quantum yield of phi(-U) = (2.86 +/- 0.80) x 10(-5), which can be partially accounted for by the cis-trans photoisomerization of usujirene to palythene (phi(U-->P) = [1.71 +/- 0.13] x 10(-5)). However, palythene in aqueous solution showed a higher photostability than did usujirene under equivalent conditions, establishing a photostationary mixture of cis-trans isomers with a relative composition of palythene-usujirene (11:1). These results may explain the preferential in vivo accumulation of palythene relative to that of usujirene observed in several dinoflagellate species.