An inventory of UV-absorbing mycosporine-like amino acids in macroalgae from polar to warm-temperate regions

A qualitative and quantitative survey of 11 green, 27 brown and 30 red macroalgal species collected from polar (Spitsbergen), cold-temperate (Helgoland) and warm-temperate (southern Spain) regions revealed that all Rhodophyceae from the eulittoral zone contained several UV-absorbing mycosporine-like amino acid compounds (MAAs), which are assumed to function as natural UV-sunscreens. In contrast, deep-water red algae, as well as the Chlorophyceae and Phaeophyceae did not contain MAAs or exhibited only trace concentrations. Within all species investigated 9 distinct compounds were found, of which 7 were identified as mycosporine-glycine, shinorine, porphyra-334, palythine, asterina-330, palythinol and palythene. The remaining two substances are unknown; they had different retention times under the chromatographic conditions used, but identical absorption spectra with a maximum at 357 nm. Both compounds are restricted to a few polar red algae. In Polysiphonia arctica J. Agardh (Rhodophyta) from Spitsbergen the concentrations of MAAs decreased from depths of 1 to 7 m. Shallow-water isolates contained > 5-fold higher total MAA amounts compared to deep-water samples. In addition, the contents of all MAAs correlated with the biogeographic region indicating that the lower the natural solar irradiance in the respective habitat the less MAAs are synthesised and accumulated. The red algal samples from Spain exhibited up to 2-fold higher MAA contents compared to species from cold-temperate and polar waters supporting the idea of a UV-dose-dependent induction and/or concentration. The data support the idea that MAAs represent a least for red macroalgae a natural defense system against exposure to biologically harmful UV-radiation.