Effects of UV irradiation on certain physiological and biochemical processes in cyanobacteria

Abstract

The effects of artificial UV (280-400 nm, 5 W m^-2) radiation on heterocyst differentiation, nitrogenase activity, ¹⁴CO₂ uptake and protein profile of whole cell and isolated heterocysts have been studied in four cyanobacterial strains isolated from Indian rice paddy fields. Exposure of cells to UV for 1 h significantly affected the differentiation of vegetative cells into heterocysts in four cyanobacterial strains studied (Anabaena sp., Nostoc sp., Nostoc carmium and Scytonema sp). Almost 50% fewer heterocysts were recorded in Anabaena sp. and Scytonema sp. and nearly 70% fewer in Nostoc sp. and Nostoc carmium after UV radiation in comparison with controls without UV. Nitrogenase activity in Anabaena sp. was completely inhibited within 45 min of UV exposure. ¹⁴CO₂ uptake in Anabaena sp. was also severely affected by UV radiation. Sodium dodecyl sulphate polyacrylamide gel electrophoresis (SDS PAGE) analyses of the total protein profile of Anabaena sp. showed a linear decrease in the protein content with increasing UV exposure time. Almost complete elimination of most of the protein bands occurred after 120 min of UV exposure. The SDS PAGE protein profile of isolated heterocysts of Anabaena sp. showed three prominent polypeptides of 26, 54 and 55 kDa, with a decrease in the first two and complete elimination of the last one after 1 h of UVradiation.