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タイトル: Circadian rhythms of resistance to UV-C and UV-B radiation in Euglena as related to 'escape from light' and 'resistance to light'
著者: Bolige, Aoen
Kiyota, Maki
Goto, Ken
後藤, 健
キーワード: antioxidant
L-ascorbic acid
circadian rhythms
dimethylsulfoxide
Euglena gracilis
photo-oxidation
UV-sensitivity
発行日: 3-Oct-2005
出版者: ELSEVIER SCIENCE SA
抄録: Radiation-induced stress, either from visible or UV light, is strongest at midday. We found that, in the absence of stress or time cues, Euglena gracilis Z was the most resistant to UV-C and UV-B at subjective midday, whether judged from immediate or reproductive survival. The circadian UV-resistance rhythms were free-running in stationary cultures under 1-h light/1-h dark cycles or continuous darkness, indicating that cell-cycle dependent DNA susceptibility to UV was not involved. We moreover examined what was the primary cause of the circadian U-V resistance, estimated as the immediate cell survival. The half-maximal lethal dose (LD50) of UV-C at subjective midday (the most resistant phase) was 156 J/m(2), which is similar to 3-fold that at subjective midnight. The same was true for UV-B, except the LD50 was similar to 13-fold that of UV-C. Temperature during UV irradiation had little effect, indicating that survival was not mediated via enzymatic reactions. Non-enzymatic antioxidants were added 5 min before UV irradiation. Dimethylsulfoxide (a hydroxyl radical scavenger) increased survival after UV-B, but had little effect after UV-C conversely, sodium ascorbate increased survival after UV-C, but not after UV-B. These findings suggest that circadian rhythms of resistance to UVs involve a common mechanism for maximizing non-enzymatic antioxidative capacity at subjective midday, but the specific antioxidants differ. (c) 2005 Elsevier B.V. All rights reserved.
URI: http://ir.obihiro.ac.jp/dspace/handle/10322/718
ISSN: 1011-1344
出現コレクション:02001学術雑誌論文

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