Effects of Ultraviolet and Photosynthetically Active Radiation on Phycocyanin of Habitat Specific Cyanobacteria

Abstract

Cyanobacteria are widely distributed and evolutionary ancient Gram-negative prokaryotes on Earth. They are highly susceptible to incoming ultraviolet radiation (UV) in the form of solar spectrum. The accessory light harvesting proteins are the first site of action of UV which affects the process of photosynthesis. We have studied the response of photosynthetically active radiation (PAR) and combination of PAR + Ultraviolet-A (UV-A) + Ultraviolet-B (UV-B) (PAB) irradiations on phycocyanin (PC), carotenoids and chlorophyll a (Chl a) of five heterocystous and non-heterocystous cyanobacterial species. We have found that Chl a had continuously declined and carotenoids was increased significantly after 24 h of exposure of PAB radiation in both heterocystous and non-heterocystous cyanobacteria. We have also recorded more decline in amount and intensity of emission fluorescence of phycocyanin (PC) in non-heterocystous as compared to heterocystous cyanobacteria in the same period of time. Similarly, fluorescence wavelength was also shifted towards shorter wavelengths. These results indicate that photosynthetic pigments of heterocystous cyanobacteria were more stable than non-heterocystous cyanobacteria. These cyanobacteria may be used as stable source for the production of value added pigments and applications in diverse field of biomedical, pharmaceutical and biotechnological sciences.