UV-MEDIATED STRESS AND ITS MITIGATION IN CYANOBACTERIA RICHA and RAJESHWAR P. SINHA* Laboratory of Photobiology and Molecular Microbiology, Centre of Advanced Study in Botany, Banaras Hindu University, Varanasi-221005 India

A substantial loss in the stratospheric ozone layer due to anthropogenically released chemicals has aroused concern about the effects of increased solar ultraviolet radiation (UVR), particularly UV-B (280-315 nm), on the Earth’s surface. Solar UV-B radiation is detrimental for most sun-exposed organisms, including humans. They can penetrate deep into biologically significant depths in lakes, ponds, rivers and oceans. Cyanobacteria, the primitive O2-evolving photosynthetic prokaryotes are solely dependent upon the solar radiation and thereby have to always face the UV-B stress. UVR affects cyanobacteria either directly or indirectly by inducing oxidative stress. In response, these organisms have developed a number of defense mechanisms such as avoidance, scavenging, screening, repair and programmed cell death to counteract its damaging effects. This review presents an overview on the effects of UVR on cyanobacteria and the defense mechanisms employed by these prokaryotes to withstand UVR stress.