Abstract
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, Anabaena sp. and Nostoc sp. ISC26 was studied over 3 days. In Anabaena sp. and Nostoc sp. ISC26, chlorophyll a (chl a) 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 a (Car/Chl a) 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 Anabaena sp. and Nostoc sp. ISC26, respectively, indicating an adaptation strategy of cyanobacteria against harmful solar short wavelength radiation especially in natural habitats.
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