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| Kiyota, Maki; Numayama, Naoko; Goto, Ken. |
| Plant defenses against photo-oxidative stress have been studied almost exclusively with respect to stress responses, and little is known about how non-enzymic antioxidants change under constant conditions without a time cue or an environmental stress. Here, we show that, in both the flagellated alga Euglena gracilis Z and the angiosperm Spinacia oleracea L., the potent antioxidant L-ascorbic acid (Asc) displays a circadian rhythm with a maximum at subjective midday, a physiological state reflecting that attained at noon under daily light/dark cycles. Thus, photosynthetic organisms can maximize antioxidant levels in anticipation of midday, when photo-oxidative stress is most severe. These results may partly explain the in-phase circadian UV-C resistance... |
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Palavras-chave: Antioxidant; L-ascorbic acid; Circadian; Euglena gracilis; Midday; Photooxidation; Spinach. |
| Ano: 2006 |
URL: http://ir.obihiro.ac.jp/dspace/handle/10322/716 |
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| Bolige, Aoen; Kiyota, Maki; Goto, Ken; 後藤, 健. |
| 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... |
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Palavras-chave: Antioxidant; L-ascorbic acid; Circadian rhythms; Dimethylsulfoxide; Euglena gracilis; Photo-oxidation; UV-sensitivity. |
| Ano: 2005 |
URL: http://ir.obihiro.ac.jp/dspace/handle/10322/718 |
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