Photochemistry and Photobiology, 20**, **: *–* Effects of PAR and UV Radiation on the Structural and Functional Integrity of Phycocyanin, Phycoerythrin and Allophycocyanin Isolated from the Marine Cyanobacterium Lyngbya sp. A09DM Rajesh Prasad Rastogi # *, Ravi Raghav Sonani # and Datta Madamwar* BRD School of Biosciences, Sardar Patel University, Anand, Gujarat, India Received 10 December 2014, accepted 4 March 2015, DOI: 10.1111/php.12449 ABSTRACT An in vitro analysis of the effects of photosynthetically active and ultraviolet radiations was executed to assess the photo- stability of biologically relevant pigments phycocyanin (PC), phycoerythrin (PE) and allophycocyanin (APC) isolated from Lyngbya sp. A09DM. Ultraviolet (UV) irradiances signifi- cantly affected the integrity of PC, PE and APC; however, PAR showed least effect. UV radiation affected the bilin chromophores covalently attached to phycobiliproteins (PBPs). Almost complete elimination of the chromophore bands associated with a- and β-subunit of PE and APC occurred after 4 h of UV-B exposure. After 5 h of UV-B exposure, the content of PC, PE and APC decreased by 51.65%, 96.8% and 96.53%, respectively. Contrary to PAR and UV-A radiation, a severe decrease in fluorescence of all PBPs was observed under UV-B irradiation. The fluorescence activity of extracted PBP was gradually inhibited immedi- ately after 15–30 min of UV-B exposure. In comparison to the PC, the fluorescence properties of PE and APC were severely lost under UV-B radiation. Moreover, the present study indicates that UV-B radiation can damage the struc- tural and functional integrity of phycobiliproteins leading to the loss of their ecological and biological functions. INTRODUCTION Cyanobacteria are most ancient (1,2), ubiquitous (3) and one of the dominant microfloras in terms of total biomass and produc- tivity in aquatic as well as terrestrial ecosystems. They are an immense source of several natural products of ecological and industrial significance (4). Moreover, during the past few dec- ades, the increase in ultraviolet (UV: 280–400 nm) radiation (5– 7) due to anthropogenically released ozone-depleting substances has generated tremendous concern about its negative impact on the biota (8–10). The core requirement of solar energy to per- form some essential metabolic functions such as N 2 -fixation and photosynthesis often exposes cyanobacteria to harmful UV-A (315–400 nm) and UV-B (280–315 nm) radiations in their natu- ral habitats that are exposed to direct solar radiation. In compari- son to UV-B radiation, UV-A radiation has a poor efficiency in inducing the cell damage, because it is not absorbed by native DNA. However, intense photosynthetically active radiation (PAR) or UV-A radiation can induce DNA damage indirectly by the generation of singlet oxygen ( 1 O 2 ) or reactive oxygen species (ROS) via indirect photosensitizing reactions (11–14). UV-B radiation has direct effects on key cellular machinery such as proteins and DNA having the absorption maxima in the range of short wavelength UV radiation (15). Moreover, increased UV-B flux over the Earth’s atmosphere can induce a number of debili- tating effects, including the pigment photo-oxidation and inacti- vation of photosystem II (PSII) in cyanobacteria (16–22). The phycobiliproteins (PBPs) such as phycocyanin (PC, k max : 610–620 nm), phycoerythrin (PE, k max : 540–570 nm) and allo- phycocyanin (APC, k max : 650–655 nm) are major photosynthetic accessory pigments of cyanobacteria, which are assembled into supramolecular light-harvesting complexes, phycobilisomes (PBS), on the stromal surfaces of the thylakoid membranes. PBPs play an important role in electron/energy transfer chain in photosynthesis. UV-induced degradation of PBPs followed by a decline of photosynthetic activity can directly influence the pri- mary productivity and community structure of the ecosystems. Furthermore, PBPs are being used as natural dyes in food, cos- metics and pharmaceutical industries as well as in different bio- medical research (23,24). Nevertheless, stability of any compounds, is the utmost requirement for their commercial application, and a few studies have been conducted on these rele- vant biomolecules, PBPs. Past research mainly focused on the effects of UV-B on the photosynthetic apparatus and D1/D2 pro- teins of photosystem-II (PSII) (16,25,26). Hence, the main objec- tive of the present study was to investigate the effects of intense PAR and UV radiation on the integrity of the ecologically and industrially important biomolecules PC, PE and APC. Further- more, the information regarding the UV effects, particularly on all PBPs (i.e. PC, PE and APC) isolated from different or the same cyanobacteria are still limited (27–29) and poorly under- stood. In the present study, we have isolated and purified the PC, PE and APC from a marine cyanobacterium Lyngbya sp. A09DM and an in vitro study was performed to analyze the structural as well as functional stability of all PBPs and associ- ated bilin chromophores under artificial intense PAR and extre- mely high energy of UV-A and UV-B radiation fluxes. MATERIALS AND METHODS Experimental organism and growth conditions. The filamentous cyano- bacterium Lyngbya sp. A09DM was originally isolated from rocky sea shores of Okha, Gujarat, India and identified by 16S rRNA gene *Corresponding authors e-mails: raj_rastogi@rediffmail.com (Rajesh Prasad Ras- togi), datta_madamwar@yahoo.com (Datta Madamwar) #These authors have contributed equally to the paper. © 2015 The American Society of Photobiology 1