Effects of solar radiation on pigmentation and induction of a mycosporine-like amino acid in two cyanobacteria, <i>Anabaena</i> sp. and <i>Nostoc</i> sp. ISC26

ABSTRACTThe effect of filtered natural solar radiation, including photosynthetically active radiation (PAR) and PAR+ultraviolet radiation (UVR), on pigmentation and synthesis of a UV absorbing ‘mycosporine-like amino acid’ (MAA) in two filamentous and heterocystous cyanobacteria, <i>Anabaena</i> sp. and <i>Nostoc</i> sp. ISC26 was studied over 3 days. In <i>Anabaena</i> sp. and <i>Nostoc</i> sp. ISC26, chlorophyll <i>a</i> (chl <i>a</i>) content decreased after 72 h to 5.45 ± 0.09 and 7.01 ± 0.54 μg mg⁻¹ DW respectively under PAR treatments; and to 4.33 ± 0.22, 6.12 ± 0.04 μg mg⁻¹ DW in PAR+UV treatments, as did carotenoids (Car) (2.68 ± 0.01, 2.93 ± 0.01 μg mg⁻¹ DW) (PAR), (2.53 ± 0.01, 2.57 ± 0.05 μg mg⁻¹ DW) (PAR+UV). A considerable increase was observed in the carotenoid:chlorophyll <i>a</i> (Car/Chl <i>a</i>) ratio as a result of carotenoid accumulation in the first 24 h and reduction of chlorophyll in the following days. A single MAA was isolated, purified by high performance liquid chromatography (HPLC) and identified as shinorine. Shinorine concentration increased significantly during 72 h specifically under PAR+UV (1270.8 ± 50.42, 2208.09 ± 73.04 nmol g⁻¹ DW) in <i>Anabaena</i> sp. and <i>Nostoc</i> sp. ISC26, respectively, indicating an adaptation strategy of cyanobacteria against harmful solar short wavelength radiation especially in natural habitats.