title: Responses of a rice-field cyanobacterium Anabaena siamensis TISTR-8012 upon exposure to PAR and UV radiation.
abstract: The effects of PAR and UV radiation and subsequent responses of certain antioxidant enzymatic and non-enzymatic defense systems were studied in a rice field cyanobacterium Anabaena siamensis TISTR 8012. UV radiation resulted in a decline in growth accompanied by a decrease in chlorophyll a and photosynthetic efficiency. Exposure of cells to UV radiation significantly affected the differentiation of vegetative cells into heterocysts or akinetes. UV-B radiation caused the fragmentation of the cyanobacterial filaments conceivably due to the observed oxidative stress. A significant increase of reactive oxygen species in vivo and DNA strand breaks were observed in UV-B exposed cells followed by those under UV-A and PAR radiation, respectively. The UV-induced oxidative damage was alleviated due to an induction of antioxidant enzymatic/non-enzymatic defense systems. In response to UV irradiation, the studied cyanobacterium exhibited a significant increase in antioxidative enzyme activities of superoxide dismutase, catalase and peroxidase. Moreover, the cyanobacterium also synthesized some UV-absorbing/screening substances. HPLC coupled with a PDA detector revealed the presence of three compounds with UV-absorption maxima at 326, 331 and 345 nm. The induction of the biosynthesis of these UV-absorbing compounds was found under both PAR and UV radiation, thus suggesting their possible function as an active photoprotectant.
authors.affiliation: Laboratory of Cyanobacterial Biotechnology, Department of Biochemistry, Faculty of Science, Chulalongkorn University, Bangkok 10330, Thailand; BRD School of Biosciences, Sardar Patel University, Vadtal Road, Satellite Campus, Post Box No. 39, Vallabh Vidyanagar 388 120, Anand, Gujarat, India. Electronic address: raj_rastogi@rediffmail.com.
authors.forename: Rajesh P
authors.initials: RP
authors.lastname: Rastogi
authors.affiliation: Laboratory of Cyanobacterial Biotechnology, Department of Biochemistry, Faculty of Science, Chulalongkorn University, Bangkok 10330, Thailand. Electronic address: aran.i@chula.ac.th.
authors.forename: Aran
authors.initials: A
authors.lastname: Incharoensakdi
authors.affiliation: BRD School of Biosciences, Sardar Patel University, Vadtal Road, Satellite Campus, Post Box No. 39, Vallabh Vidyanagar 388 120, Anand, Gujarat, India. Electronic address: datta_madamwar@yahoo.com.
authors.forename: Datta
authors.initials: D
authors.lastname: Madamwar
mesh_terms: D017033:Anabaena / Q000235:genetics / Q000254:growth & development / Q000502:physiology* / Q000528:radiation effects*; D000975:Antioxidants / Q000378:metabolism / Q000528:radiation effects; D002734:Chlorophyll / Q000378:metabolism / Q000528:radiation effects; D000077194:Chlorophyll A; D004249:DNA Damage / Q000528:radiation effects; D008027:Light; D018384:Oxidative Stress / Q000528:radiation effects; D010788:Photosynthesis / Q000528:radiation effects; D017382:Reactive Oxygen Species / Q000378:metabolism / Q000528:radiation effects; D013050:Spectrometry, Fluorescence; D014466:Ultraviolet Rays
chemical_list: D000975:Antioxidants; D017382:Reactive Oxygen Species; D002734:Chlorophyll; D000077194:Chlorophyll A
keywords: Antioxidant system; Cyanobacteria; Oxidative damage; Sunscreens; UV radiation