Natural ultraviolet radiation and photosynthetically active radiation induce formation of mycosporine-like amino acids in the marine macroalga Chondrus crispus (Rhodophyta)

The UV-absorbing mycosporine-like amino acids (MAAs) are hypothesized to protect organisms against harmful UV radiation (UVR). Since the physiology and metabolism of these compounds are unknown, the induction and kinetics of MAA biosynthesis by various natural radiation conditions were investigated in the marine red alga Chondrus crispus collected from Helgoland, Germany. Three photosynthetically active radiation (PAR, 400–700 nm) treatments without UVR and three UV-A/B (290–400 nm) treatments without PAR were given. Chondrus crispus collected from 4–6 m depth contained only traces of the MAA palythine. After 24 h exposure to 100% ambient PAR, traces of three additional MAAs, shinorine, palythinol and palythene, were detected, and their concentrations increased strongly during a one-week exposure to all PAR treatments. The concentration of all MAAs varied directly with PAR dose, with palythine and shinorine being four- to sevenfold higher than palythinol and palythene. Likewise, naturally high doses of both UV-A and UV-B resulted in a strong accumulation of all MAAs, in particular shinorine. While shinorine accumulation was much more stimulated by UVR, the content of all other MAAs was more affected by high PAR, indicating an MAA-specific induction triggered by UVR or PAR. Received: 24 September 1997 / Accepted: 17 December 1997     

Wavelength-dependent induction of UV-absorbing mycosporine-like amino acids in the red alga Chondrus crispus under natural solar radiation

Polychromatic response spectra for the induction of UV absorbing mycosporine-like amino acids (MAAs) were calculated after exposing small thalli of the red alga Chondrus crispus under various cut-off filters to natural solar radiation on the North Sea island Helgoland, Germany. The laboratory-grown specimens typically contain only traces of palythine and synthesise five different MAAs rapidly and in high concentrations after being transplanted into shallow water. The resulting qualitative and quantitative patterns of MAA induction differed markedly with respect to spectral distribution. Furthermore, the wavebands effective for MAA induction vary within the MAA. UV-B radiation had a negative effect on the accumulation of the major MAAs shinorine (λ_max=334 nm) and palythine (λ_max=320 nm), while short wavelength UV-A exhibits the highest quantum efficiency on their synthesis. In contrast, the synthesis of asterina-330 (λ_max=330 nm), palythinol (λ_max=332 nm) and palythene (λ_max=360 nm) was mainly induced by UV-B radiation. Whether the synthesis of shinorine and palythine is induced by a photoreceptor with an absorption maximum in the short wavelength UV-A and whether a second photoreceptor absorbing UV-B radiation is responsible for the induction of asterina-330, palythinol and palythene remains to be studied.Our results show that C. crispus has a high capacity to adapt flexibly the qualitative and quantitative MAA concentration to the prevailing spectral distribution of irradiance. On one hand, this is regarded as an important aspect with respect to the acclimation of algae to increasing UV-B irradiance in the context of ongoing depletion of stratospheric ozone. On the other hand, the experiment demonstrates that UV-A irradiance is more important for the induction of the major MAAs shinorine and palythine than UV-B.     

Ultraviolet and osmotic stresses induce and regulate the synthesis of mycosporines in the cyanobacterium Chlorogloeopsis PCC 6912

The cyanobacterium Chlorogloeopsis PCC 6912 was found to synthesize and accumulate two putative UV sunscreen compounds of the mycosporine (mycosporine-like amino acid; MAA) type: mycosporine-glycine and shinorine. These MAAs were not constitutively present in the cells; their synthesis could be induced specifically either by exposure to UVB radiation (280–320 nm) or by osmotic stress, but not by other stress factors such as heat or cold shock, nutrient limitation, or photooxidative stress. A significant synergistic enhancement of MAA synthesis was observed when both stress factors were applied in combination. Although osmotic stress could induce MAA synthesis, comparison of the intracellular contents of MAAs with those of sugar osmolytes (glucose and trehalose) indicated that MAAs play no significant role in attaining osmotic homeostasis. UVB strongly enhanced the accumulation of shinorine, whereas osmotic stress had a more pronounced effect on mycosporine-glycine. This differential effect on the steady-state contents of each MAA could be explained either by differential regulation of biosynthesis or by differential loss rates of MAAs (leakage) under each condition. A preferential leakage of mycosporine-glycine from the cells after a hypoosmotic shock was detected. The results are interpreted in terms of an adaptive necessity for a combined regulatory control responding to both UV and external osmotic conditions in organisms that accumulate water-soluble sunscreens intracellularly. Received: 26 March 1999 / Accepted: 13 July 1999     

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.     

The relative contributions of diet and associated microbiota to the accumulation of UV‐absorbing mycosporine‐like amino acids in the freshwater copepod Boeckella antiqua

1. Mycosporine‐like amino acids (MAAs) are ubiquitous compounds in aquatic organisms that are usually considered sunscreens that protect them from harmful ultraviolet radiation. Given that virtually all animals lack the metabolic pathways to synthesise MAAs de novo, they must acquire them either from their diet or from microorganisms living in close association. In freshwater copepods, accumulation of MAAs is stimulated by exposure to ultraviolet and/or visible radiation. 2. A 2 × 2 factorial experiment was performed to assess the contributions of dietary and microbial sources of MAAs in the freshwater copepod Boeckella antiqua. The treatments consisted of two different diets: an MAA‐free diet, including only Chlamydomonas reinhardtii, and an MAA‐rich diet, including both C. reinhardtii and Peridinium inconspicuum, crossed with two antibiotic treatments, with and without chloramphenicol. Treatment with chloramphenicol was intended to inhibit the development of bacteria associated with the copepods. 3. MAA concentration in B. antiqua was affected by the experimental conditions: (i) exposure to artificial PAR + UVR stimulated the accumulation of several MAAs (up to 62% increase in total MAA concentration with respect to the initial concentration); (ii) the presence of chloramphenicol in the culture media reduced the MAA concentration in copepods fed an MAA‐free diet; (iii) in the absence of chloramphenicol, copepods fed the MAA‐rich diet had significantly higher total MAA concentration than those fed the MAA‐deficient diet; but (iv) dietary supplementation with an MAA‐rich algae in the presence of chloramphenicol failed to significantly increase total MAA concentration. 4. Analysis of profiles from denaturing gradient gel electrophoresis (DGGE) showed that the prokaryotic community associated with the copepods was affected by chloramphenicol. Dendograms constructed from digitalised DGGE images consistently grouped the antibiotics treatments separately from the initial samples and the treatments without antibiotics. Two band positions were exclusive to treatments without antibiotics. 5. We conclude that when offered an MAA‐rich diet, B. antiqua may accumulate a proportion of MAAs from diet. However, we suspect that in the absence of an MAA‐rich dietary source (as in its natural habitat), virtually all MAAs present in B. antiqua are produced by copepod‐associated prokaryotes.     

Mycosporine-like amino acid content in four species of sea anemones in the genus Anthopleura reflects phylogenetic but not environmental or symbiotic relationships

We examine the occurrence of UV-absorbing, mycosporine-like amino acids (MAAs) in four sympatric species of sea anemones in the genus Anthopleura, all collected from intertidal habitats on the Pacific Coast of temperate North America. We compare patterns of MAAs in A. elegantissima of several types: specimens having predominately zooxanthellae (dinoflagellates comprising at least two species) or zoochlorellae as symbionts; those containing algal endosymbionts of both kinds, and naturally occurring aposymbiotic specimens that lack the endosymbionts typically found in most specimens. We also compare MAAs in zooxanthellate specimens of A. sola and A. xanthogrammica, and specimens from the asymbiotic species A. artemisia. Our findings indicate that the complements of the four major MAAs in these species of Anthopleura (mycosporine-taurine, shinorine, porphyra-334, and mycosporine-2 glycine) broadly reflect phylogenetic differences among the anemones rather than the taxon of endosymbionts, presence or absence of symbionts, or environmental factors. An exception, however, occurs in A. elegantissima, where mycosporine-2 glycine increases in concentration with the density of zooxanthellae. Our evidence also shows that A. elegantissima can accumulate MAAs from its food, which may explain the occasional occurrence of minor MAAs in some individuals.     

Photoheterotrophic growth unprecedentedly increases the biosynthesis of mycosporine-like amino acid shinorine in the cyanobacterium Anabaena sp., isolated from hot springs of Rajgir (India)

Cyanobacteria are known to biosynthesize mycosporine-like amino acids (MAAs) as photoprotective compounds against ultraviolet radiation. Anabaena sp., isolated from the hot springs of Rajgir, India, produces a single MAA shinorine (retention time = 2.2 min and absorption maximum at 334 nm) as purified by high-performance liquid chromatography. The MAA biosynthesis was under constitutive control in this cyanobacterium; however, PAR + UV-A + UV-B radiation was found to have highest impact on MAA synthesis. MAA biosynthesis is dependent on photosynthesis for the carbon source since the inhibitory effect of DCMU on MAA synthesis was overcome by externally added fructose. Our results suggest that there is no direct involvement of photosystem II dependent linear electron transport in MAA biosynthesis. However, utilization of energy derived from photosystem I dependent cyclic electron transport in MAA biosynthesis cannot be ruled out. This study also reveals that photoheterotrophic growth can support highest MAA biosynthesis under laboratory conditions in comparison with photoautotrophic and photomixotrophic growth. Thus, photoheterotrophic growth condition can be used for the large-scale production of pharmaceutically important MAAs from cyanobacteria for an industrial application.     

Discovery of Gene Cluster for Mycosporine-Like Amino Acid Biosynthesis from Actinomycetales Microorganisms and Production of a Novel Mycosporine-Like Amino Acid by Heterologous Expression

Mycosporines and mycosporine-like amino acids (MAAs), including shinorine (mycosporine-glycine-serine) and porphyra-334 (mycosporine-glycine-threonine), are UV-absorbing compounds produced by cyanobacteria, fungi, and marine micro- and macroalgae. These MAAs have the ability to protect these organisms from damage by environmental UV radiation. Although no reports have described the production of MAAs and the corresponding genes involved in MAA biosynthesis from Gram-positive bacteria to date, genome mining of the Gram-positive bacterial database revealed that two microorganisms belonging to the order Actinomycetales, Actinosynnema mirum DSM 43827 and Pseudonocardia sp. strain P1, possess a gene cluster homologous to the biosynthetic gene clusters identified from cyanobacteria. When the two strains were grown in liquid culture, Pseudonocardia sp. accumulated a very small amount of MAA-like compound in a medium-dependent manner, whereas A. mirum did not produce MAAs under any culture conditions, indicating that the biosynthetic gene cluster of A. mirum was in a cryptic state in this microorganism. In order to characterize these biosynthetic gene clusters, each biosynthetic gene cluster was heterologously expressed in an engineered host, Streptomyces avermitilis SUKA22. Since the resultant transformants carrying the entire biosynthetic gene cluster controlled by an alternative promoter produced mainly shinorine, this is the first confirmation of a biosynthetic gene cluster for MAA from Gram-positive bacteria. Furthermore, S. avermitilis SUKA22 transformants carrying the biosynthetic gene cluster for MAA of A. mirum accumulated not only shinorine and porphyra-334 but also a novel MAA. Structure elucidation revealed that the novel MAA is mycosporine-glycine-alanine, which substitutes l-alanine for the l-serine of shinorine.     

Contents of ultraviolet-absorbing substances in two color morphs of the photosymbiotic ascidian Didemnum molle

The contents of mycosporine-like amino acids (MAAs) were compared in the two color morphs (dark-gray and brown colonies) of the tropical ascidian Didemnum molle (Herdman, 1886), which harbors the photosymbiotic prokaryote Prochloron. The colonies of each color morph were exclusively distributed in shallow reef lagoons at the different sites. Spectroscopic and chromatographic analyses showed that the Prochloron cell density and MAA concentration in the dark-gray colonies were an estimated 1.4 and 2.4 times higher, respectively, than in the brown colonies. The significant difference in MAA contents between the color morphs was primarily due to the difference in shinorine contents (p < 0.01, Mann–Whitney U-test). The high concentration of MAAs in the dark-gray colonies may provide better conditions for Prochloron cells, compared to the brown colonies with lower MAA concentrations.     

Mycosporine-like amino acid (MAAs) production by Heterocapasa sp. (Dinophyceae) in indoor cultures

The possibility of using mycosporine-like amino acids (MAAs), with an apparent sunscreen function in nature, as ultraviolet radiation (UVR) blockers to prevent skin injury has been raised by diverse authors. Production of MAAs by the dinoflagellate Heterocapsa sp. (Dinophyceae) is shown here. Three major peaks with absorption maxima at 330.8, 332.0 and 333.2 nm were detected by high performance liquid chromatography (HPLC) analysis of methanolic extracts in all tested conditions. Analysis of crude extract by mass spectroscopy with electrospray ionization (MS-EI) showed a set of molecular ions ([M+H](+)) with main peaks being at m/z 242.4, 288.4, 303.3 and 333.3 u.m.a. According to these data, along with retention times, the MAA profile of Heterocapsa sp. is assumed to be composed of shinorine (lambda(max)=334 nm), mycosporine-2-glycine (lambda(max)=331 nm) and palythinol (lambda(max)=332 nm). A constitutive MAA content of about 4 microg (10(6) cells)(-1) was measured under exposure to PAR only. A maximal accumulation of MAA per culture volume of 1.1 mg l(-1) was obtained after 72 h of exposure to PAR+UVA, while the highest production rate (0.025 mg l(-1) h(-1)) was computed after 24 h of exposure to PAR+UVA+UVB.     

Ultraviolet radiation-absorbing mycosporine-like amino acids (MAAs) are acquired from their diet by medaka fish (Oryzias latipes) but not by SKH-1 hairless mice

To assess whether vertebrates can acquire, from their diet, ultraviolet radiation-absorbing mycosporine-like amino acids (MAAs), medaka fish and hairless mice were maintained for 150 and 130 days, respectively, on diets either including Mastocarpus stellatus (rich in MAAs) or the same diets without this red alga. In medaka, the MAAs palythine and asterina-330, present in trace quantities in the diet with added M. stellatus, were present in significantly greater quantities in the eyes of fish fed this diet than in the eyes of control fish. Only traces of MAAs were present in the skin of medaka fed the diet containing MAAs. Shinorine, the principal MAA in M. stellatus, was not found in any tissues of medaka, which raises questions about the specificity of transport of MAAs. In hairless mice, no dietary MAAs were found in the tissues of the eyes, skin, or liver after maintenance on the experimental diet. Low concentrations of shinorine were present only in the tissues of the small and large intestines. These results indicate that MAAs are acquired from their diet and translocated to superficial tissues by teleost fish, but that mammals may be incapable of such. Thus, dietary supplementation with MAAs may be useful in aquacultured species of fish, but MAAs as ‘dietary sunscreens' may not be an option for mammals, including humans. Nevertheless, our demonstration of the uptake of shinorine by human skin cancer cells in culture raises evolutionary questions regarding the organ specificity of the capacity for the cellular transport of MAAs.     

BLUE LIGHT AND UV-A RADIATION CONTROL THE SYNTHESIS OF MYCOSPORINE-LIKE AMINO ACIDS IN CHONDRUS CRISPUS (FLORIDEOPHYCEAE)

The induction of UV-absorbing compounds known as mycosporine-like amino acids (MAAs) by red, green, blue, and white light (43% ambient radiation greater than 390 nm) was examined in sublittoral Chondrus crispus Stackh. Fresh collections or long-term cultures of sublittoral thalli, collected from Helgoland, North Sea, Germany, and containing no measurable amounts of MAAs, were exposed to filtered natural radiation for up to 40 days. The MAA palythine (λ_max 320 nm) was synthesized in thalli in blue light to the same extent observed in control samples in white light. In contrast, thalli in green or red light contained only trace amounts of MAAs. After the growth and synthesis period, the photosynthetic performance of thalli in each treatment, measured as pulse amplitude modulated chlorophyll fluorescence, was assessed after a defined UV dose in the laboratory. Thalli with MAAs were more resistant to UV than those without, and exposure to UV-A+B was more damaging than UV-A in that optimal (F_v/F_m) and effective (φ_II) quantum yields were lower and a greater proportion of the primary electron acceptor of PSII, Q, became reduced at saturating irradiance. However, blue light-grown thalli were generally more sensitive than white light control samples to UV-A despite having similar amounts of MAAs. The most sensitive thalli were those grown in red light, which had significantly greater reductions in F_v/F_m and φ_II and greater Q reduction. Growth under UV radiation alone had been shown previously to lead to the synthesis of the MAA shinorine (λ_max 334 nm) rather than palythine. In further experiments, we found that preexposure to blue light followed by growth in natural UV-A led to a 7-fold increase in the synthesis of shinorine, compared with growth in UV-A or UV-A+B without blue light pretreatment. We hypothesize that there are two photoreceptors for MAA synthesis in C. crispus, one for blue light and one for UV-A, which can act synergistically. This system would predispose C. crispus to efficiently synthesize UV protective compounds when radiation levels are rising, for example, on a seasonal basis. However, because the UV-B increase associated with artificial ozone reduction will not be accompanied by an increase in blue light, this triggering mechanism will have little additional adaptive value in the face of global change unless a global UV-B increase positively affects water column clarity.     

Effects of salinity and ultraviolet radiation on the concentration of mycosporine-like amino acids in various isolates of the benthic cyanobacterium Microcoleus chthonoplastes

The effects of salinity and ultraviolet B (UV‐B) treatment on the intracellular mycosporine‐like amino acid (MAA) concentration in three isolates of the benthic cyanobacterium Microcoleus chthonoplastes from the Baltic Sea (WIS), Spain (EBD) and Australia (TOW) were compared. All strains contained shinorine and, in addition, both EBD and TOW exhibited the unknown MAA‐332, and WIS exhibited the unknown MAA‐346. Salinity treatment led to MAA accumulation in TOW and WIS, but not in EBD. Whereas UV‐B exposure was accompanied by a strong increase in MAA in EBD and TOW, WIS did not survive the treatment. All data indicate isolate‐specific MAA accumulation patterns under different environmental conditions and can be explained by ecotypic differentiation. A double function of MAAs as organic osmolytes and photoprotect‐ants seems possible.     

Mycosporine-like amino acids (MAAs) profile of a rice-field cyanobacterium Anabaena doliolum as influenced by PAR and UVR

The mycosporine-like amino acid (MAA) profile of a rice-field cyanobacterium, Anabaena doliolum, was studied under PAR and PAR + UVR conditions. The high-performance liquid chromatographic analysis of water-soluble compounds reveals the biosynthesis of three MAAs, mycosporine-glycine (lambda (max) = 310 nm), porphyra-334 (lambda (max) = 334 nm) and shinorine (lambda (max) = 334 nm), with retention times of 4.1, 3.5 and 2.3 min, respectively. This is the first report for the occurrence of mycosporine-glycine and porphyra-334 in addition to shinorine in Anabaena strains studied so far. The results indicate that mycosporine-glycine (monosubstituted) acts as a precursor for the biosynthesis of the bisubstituted MAAs shinorine and porphyra-334. Mycosporine-glycine was under constitutive control while porphyra-334 and shinorine were induced by UV-B radiation, indicating the involvement of UV-regulated enzymes in the biotransformation of MAAs. It seems that A. doliolum is able to protect its cell machinery from UVR by synthesizing a complex set of MAAs and thus is able to survive successfully during the summer in its natural brightly lit habitats.     

Temporal concentrations of sunscreen compounds (Mycosporine-like Amino Acids) in phytoplankton and in the New Zealand krill, Nyctiphanes australis G.O. Sars

This study investigated the relationship between seasonal changesin ambient UV-R, and sunscreen concentrations in phytoplanktonand krill. Concentrations of mycosprine-like amino acid (MAA)sunscreens were quantified in phytoplankton communities andin the krill Nyctiphanes australis over a 1-year period offthe Otago Coast, New Zealand. Ambient UV-B and UV-A ranged froma minimum mean daily dose of 2.19 x 10⁴ kJ day^–1 and 0.73x 10⁶ kJ day^–1 in June, to a maximum in January of 20.19x 10⁴ kJ day^–1 and 4.88 x 10⁶ kJ day^–1, respectively.Concentrations of MAAs (consisting almost entirely of Mycosporine-glycine)in the phytoplankton community were lowest in August (5.6 nmolµg^–1 Chl) when UV-R irradiances were minimal andhighest in January (41.4 nmol µg^–1 Chl) when UV-Rirradiances were maximal. Nyctiphanes australis was found tocontain five identified MAAs (mycosporine-glycine, shinorine,Porphyra-334, palythine and palythinol) and several unknownUV-R absorbing compounds. Concentrations ranged from 4.73 to15.51 nmol mg^–1 dw, with little indication of a seasonalcycle that could be correlated with changes in either phytoplanktonMAA concentrations or ambient UV-R irradiances. The findingssuggest that krill are neither accumulating MAAs in responseto changes in MAA concentrations in their phytoplankton food,or that MAA concentrations in krill are increased in responseto higher ambient UV-R irradiances. Concentrations of MAAs inkrill body parts (carapace, legs, eyes, antennae, muscle) weresimilar (4.89–5.98 nmol mg^–1 dw), with the exceptionof the carapace (2.03 nmol mg^–1 dw).     

Ultraviolet sunscreen compounds in epiphytic red algae from mangroves

Epiphytic red algae of the order Ceramiales from mangroves and salt marshes (nine species from Bostrychia, three from Stictosiphonia and four from Caloglossa) produce varying levels of the UV-absorbing compounds mycosporine-glycine, shinorine, porphyra-334, palythine, asterina-330 and palythinol, a suite of substances chemically assigned as mycosporine-like amino acids (MAAs). Mean MAA levels varied from 0.02 to 12.8 mg g^–1 DW in field-collected and laboratory cultured specimens. While in field samples of Bostrychia montagneiHarvey, Bostrychia radicans (Montagne) Montagne and Caloglossa apomeiotica J.West et G.Zuccarello MAA concentrations were generally higher compared to cultured plants of the same taxa, Bostrychia tenella(Lamouroux) J.Agardh did not show such a difference. Catenella caespitosa (Withering) L.Irvine, Catenella impudica (Montagne) J.Agardh and Catenella nipae Zanardini (Gigartinales, Caulacanthaceae) produce two novel UV-absorbing compounds: MAA-1 (1.4–4.3 mg g ^–1 DW) and MAA-2 (0.1–1.0 mg g^–1 DW), which absorb at 334 nm and 320 nm, respectively. In laboratory culture of Bostrychia moritziana when photosynthetically active radiation (PAR) was increased from 20 to 40 mol photons m^–2 s^–1, the total level of palythinol increased by 85% (from 2.0 to 3.7 mg g^–1 DW). In a culture of Caloglossa leprieurii when PAR was increased from 40 to 80 mol m^–2 s^–1the porphyra-334 content increased by 77% (from 3.1 to 5.5 mg g^–1 DW). Extremely high MAA contents of >30 mg g^–1 DW were detected in mature tetrasporangial sori prepared from two isolates of laboratory-cultured reproductive Caloglossa apomeiotica compared to vegetative plants (about 10 mg MAAs g^–1 DW) indicating tetraspores loaded up with UV-sunscreens. All data demonstrate that mangrove red algae contain high MAA concentrations, particularly the reproductive structures, and hence these compounds may act as biochemical photoprotectants against exposure to UV-radiation.     

SYNTHESIS OF MYCOSPORINE-LIKE AMINO ACIDS IN CHONDRUS CRISPUS (FLORIDEOPHYCEAE) AND THE CONSEQUENCES FOR SENSITIVITY TO ULTRAVIOLET B RADIATION

The induction and protective role of the UV-absorbing compounds known as mycosporine-like amino acids (MAAs) were examined in sublittoral Chondrus crispus Stackh. transplanted for 2 weeks in the spring and summer to shallow water under three irradiance conditions: PAR (photosynthetically active radiation; 400–700 nm), PAR + UVA (PAR + 320– 400 nm), PAR + UVA + UVB (PAR + UVA + 280– 320 nm). Sublittoral thalli collected around Helgoland, North Sea, Germany, from 6 m below the mean low water of spring tides contained less than 0.1 mg·g⁻¹ dry weight (DW) total MAAs, whereas eulittoral samples contained over 1 mg·g⁻¹ DW. Transplantation to shallow water led to the immediate synthesis of three MAAs in the following temporal order: shinorine (λ_max 334 nm), asterina (λ_max 330 nm), and palythine (λ_max 320 nm), with the shinorine content peaking and then declining after 2 days (exposure to 100 mol photons·m⁻²). Maximum total MAA content (2 mg·g⁻¹ DW) also occurred after 2 days of induction, exceeding the content normally found in eulittoral samples. Furthermore, the relative proportion of the different MAAs at this time was different than that in eulittoral samples. After 2 days the total content declined to the eulittoral value, with palythine as the principal MAA. Similar data were obtained for all treatments, indicating that MAA synthesis in C. crispus was induced by PAR and not especially stimulated by UV radiation. The ability of photosystem II (PSII) to resist damage by UVB was tested periodically during the acclimation period by exposing samples to a defined UVB dose in the lab. Changes in chlorophyll fluorescence (F_v/F_m and effective quantum yield, φ_II) indicated that PSII function was inhibited during the initial stage of acclimation but gradually improved with time. No difference among screening treatments was detected except in spring for the samples acclimating to PAR + UVA + UVB. In this treatment F_v/F_m and φ_II were significantly lower than in the other treatments. During the first week of each experiment, growth rates were also significantly reduced by UVB. The reductions occurred despite maximum MAA content, indicating an incomplete protection of photosynthetic and growth-related processes.     

The distribution of mycosporine-like amino acids (MAAs) and the phylogenetic identity of symbiotic dinoflagellates in cnidarian hosts from the Mexican Caribbean

A survey of 54 species of symbiotic cnidarians that included hydrozoan corals, anemones, gorgonians and scleractinian corals was conducted in the Mexican Caribbean for the presence of mycosporine-like amino acids (MAAs) in the host as well as the Symbiodinium fractions. The host fractions contained relatively simple MAA profiles, all harbouring between one and three MAAs, principally mycosporine-glycine followed by shinorine and porphyra-334 in smaller amounts. Symbiodinium populations were identified to sub-generic levels using PCR-DGGE analysis of the Internal Transcribed Spacer 2 (ITS2) region. Regardless of clade identity, all Symbiodinium extracts contained MAAs, in contrast to the pattern that has been found in cultures of Symbiodinium, where clade A symbionts produced MAAs whereas clade B, C, D, and E symbionts did not. Under natural conditions between one and four MAAs were identified in the symbiont fractions, mycosporine-glycine (λ_max = 310 nm), shinorine (λ_max = 334 nm), porphyra-334 (λ_max = 334 nm) and palythine (λ_max = 320 nm). One sample also contained mycosporine-2-glycine (λ_max = 331 nm). These data suggest that Symbiodinium is restricted to producing five MAAs and there also appears to be a defined order of appearance of these MAAs: mycosporine-glycine followed by shinorine (in one case mycosporine-2-glycine), then porphyra-334 and palythine. Overall, mycosporine-glycine was found in highest concentrations in the host and symbiont extracts. This MAA, unlike many other MAAs, absorbs within the ultraviolet-B range (UVB, 280-320 nm) and is also known for moderate antioxidant properties thus potentially providing protection against the direct and indirect effects of UVR. No depth-dependent changes could be identified due to a high variability of MAA concentrations when all species were included in the analysis. The presence of at least one MAA in all symbiont and host fractions analyzed serves to highlight the importance of MAAs, and in particular the role of mycosporine-glycine, as photoprotectants in the coral reef environment.     

Role of various growth media on shinorine (mycosporine-like amino acid) concentration and photosynthetic yield in <Emphasis Type="Italic">Anabaena variabilis</Emphasis> PCC 7937

The induction of shinorine (mycosporine-like amino acid (MAA)) in Anabaena variabilis PCC 7937 was studied in various culture media (BGA⁻, BGA⁺, BG11 and Allen and Arnon’s). The objective was to select the most appropriate medium that can support the highest induction of MAAs and can be used for industrial production of these UV protective substances from cyanobacteria. Also, in vivo photosynthetic activity was measured under shinorine inducing conditions in all media. The shinorine content and photosynthetic activity (yield) were highest (2948.73 ± 61.13 nmol/g dry wt and 0.47 ± 0.01, respectively) in BG11 medium in comparison to others after 72 h of UV radiation. After the same duration of irradiation shinorine content was 1076.08 ± 21.77, 1320.07 ± 98.19 and 554.64 ± 16.47 nmol/g dry wt in BGA⁻, BGA⁺, and Allen and Arnon’s media, respectively. Thus, BG11 medium can be used for mass production of MAAs from cyanobacteria.