Ultraviolet sunscreen compounds in epiphytic red algae from mangroves

Abstract

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 μmol 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 μmol 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.