Effects of ultravjolet-B radiation in three rice field cyanobacteria

Abstract

Summary The effects of artificial ultraviolet-B (UV-B; 280-315 nm; 2.5 Wm −2 ) radiation on survival, growth, pigmentation, and total protein profile have been studied in three cyanobacterial strains, Nostoc sp., Calothrix pulvinata and Plectonema boryanum , isolated from rice (paddy) fields in India. Differential sensitivity of individual species to UV-B irradiation were recorded in this investigation. P. boryanum failed to survive 180 min of UV-B irradiation, whereas the brown Nostoc sp. and C. pulvinata survived the same duration of irradiation. Growth patterns of the organisms treated with UV-B revealed that Nostoc sp. was comparatively more tolerant than C. pulvinata and P. boryanum . Phycocyanin (K max 620 nm) was severely affected by UV-B irradiation in all strains; the degree of pigment bleaching was most pronounced in P. boryanum followed by C. pulvinata and Nostoc sp. Phycoerythrin(λ max 560 nm) was also bleached considerably in Nostoc sp. and C. pulvinata; P. boryanum does not contain phycoerythrin. There was also a significant drop in the absorption of Chl a after UV-B irradiation in all strains. Fluorescence emission decreased considerably in all organisms with increasing UV-B irradiation time. SDS-PAGE analyses of the total protein profile of the organisms showed a linear decrease in the protein content with increasing UV-B irradiation time. Complete loss of most of the protein bands occurred after UV-B irradiation of 60 min in P. boryanum and 120 min in C. pulvinata , whereas there was only little effect in the brown Nostoc sp. even after 180 min of UV-B irradiation. Phycoerythrin (26 kDa) in Nostoc sp. was less affected by UV-B irradiation than phycocyanin (20 kDa) in P. boryanum .