Induction of mycosporine-like amino acids (MAAS) in cyanobacteria by solarultraviolet-B radiation

Three filamentous and heterocystous N-2-fixing cyanobacteria, Anabaena sp., Nostoc commune and Scytonema sp. were tested for the presence of ultraviol et-absorbing mycosporine-like amino acids (MAAs) and their induction by sol ar 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 contai ning 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 Union, Rawson, Chubut, Patagonia, Argentina) for 3 days, 4 -6th February, 2000. Solar radiation was measured by an ELDONET (European L ight Dosimeter Network) filter radiometer permanently installed on the roof of the Estacion de Fotobiologia Playa Union (43 degrees 18' S; 65 degrees 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 cy anobacteria. Shinorine was found to be induced mostly during the light peri od. During the dark period the concentration stayed almost constant. In add ition to shinorine, another unidentified, water-soluble, brownish compound with an absorption maximum at 315 nm was found to be induced by UV-B only i n Scytonema sp. and released into the medium. This substance was neither fo und in Anabaena sp. nor in Nostoc commune. Judging from the results, the st udied cyanobacteria may protect themselves from deleterious short wavelengt h radiation by their ability to synthesize photoprotective compounds in res ponse to UV-B radiation. (C) 2001 Elsevier Science BY. All rights reserved.