title: Photoreactivation in Paramecium tetraurelia under conditions of various degrees of ozone layer depletion.
abstract: Photoreactivation (PR) is an efficient survival mechanism that helps protect cells against the harmful effects of solar-ultraviolet (UV) radiation. The PR mechanism involves photolyase, just one enzyme, and can repair DNA damage, such as cyclobutane-pyrimidine dimers (CPD) induced by near-UV/blue light, a component of sunlight. Although the balance of near-UV/blue light and far-UV light reaching the Earth's surface could be altered by the atmospheric ozone layer's depletion, experiments simulating this environmental change and its possible effects on life have not yet been performed. To quantify the strength of UVB in sunlight reaching the Earth's surface, we measured the number of CPD generated in plasmid DNA after UVB irradiation or exposure to sunlight. To simulate the increase of solar-UV radiation resulting from the ozone layer depletion, Paramecium tetraurelia was exposed to UVB and/or sunlight in clear summer weather. PR recovery after exposure to sunlight was complete at a low dose rate of 0.2 J/m2 x s, but was less efficient when the dose rate was increased by a factor of 2.5 to 0.5 J/m2 x s. It is suggested that solar-UV radiation would not influence the cell growth of P. tetraurelia for the reason of high PR activity even when the ozone concentration was decreased 30% from the present levels.
authors.affiliation: Department of Biology, Nara Medical University School of Medicine, Japan.
authors.forename: Akihisa
authors.initials: A
authors.lastname: Takahashi
authors.forename: Toshihiro
authors.initials: T
authors.lastname: Kumatani
authors.forename: Saori
authors.initials: S
authors.lastname: Usui
authors.forename: Ryoko
authors.initials: R
authors.lastname: Tsujimura
authors.forename: Takaharu
authors.initials: T
authors.lastname: Seki
authors.forename: Kouichi
authors.initials: K
authors.lastname: Morimoto
authors.forename: Takeo
authors.initials: T
authors.lastname: Ohnishi
mesh_terms: D000818:Animals; D008027:Light; D010126:Ozone / Q000633:toxicity*; D016805:Paramecium tetraurelia / Q000528:radiation effects*; D013472:Sunlight; D014466:Ultraviolet Rays
chemical_list: D010126:Ozone