Takahashi Akihisa, Kumatani Toshihiro, Usui Saori, Tsujimura Ryoko, Seki Takaharu, Morimoto Kouichi, Ohnishi Takeo
Department of Biology, Nara Medical University School of Medicine, Japan.
Photochem Photobiol. 2005 Jul-Aug;81(4):1010-4. doi: 10.1562/2005-03-16-RA-463.
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.
光复活作用（PR）是一种有效的生存机制，有助于保护细胞免受太阳紫外线（UV）辐射的有害影响。PR机制涉及光解酶，这是一种单一的酶，并且能够修复DNA损伤，比如由近紫外光/蓝光（阳光的一个组成部分）诱导产生的环丁烷嘧啶二聚体（CPD）。尽管到达地球表面的近紫外光/蓝光和远紫外光的平衡可能会因大气臭氧层的损耗而改变，但尚未进行模拟这种环境变化及其对生命可能产生的影响的实验。为了量化到达地球表面的阳光中UVB的强度，我们测量了UVB照射或暴露于阳光下后质粒DNA中产生的CPD数量。为了模拟臭氧层损耗导致的太阳紫外线辐射增加，在晴朗的夏季天气中，将四膜虫暴露于UVB和/或阳光下。在0.2 J/m2×s的低剂量率下，暴露于阳光下后的PR恢复是完全的，但当剂量率增加2.5倍至0.5 J/m2×s时，效率较低。有人认为，即使臭氧浓度从当前水平降低30%，由于PR活性高，太阳紫外线辐射也不会影响四膜虫的细胞生长。
