Abstract:
Purpose : Circadian rhythms of resistance to ultraviolet (UV) irradiation help prevent UV-induced damage
during daytime hours in the photosynthetic organisms. The present study was performed to identify the primary
causes of these rhythms using unicellular microalgal flagellate Euglena gracilis as a model.
Research Method : We examined the dose-response effects of the exogenous supplementation of 25 different
antioxidants on enhancing resistance in E. gracilis to UV-C irradiation based on its immediate survival. We also
compared radical scavenging and singlet-molecular-oxygen (1
O2
)-quenching activities of each antioxidant in
homogeneous ethanol solutions.
Findings : Several antioxidants enhanced UV-C resistance at the least resistant phase to levels greater than
or equal to levels achieved physiologically at the most resistant phase, suggesting that the antioxidants (or
their physiological counterparts) may be under circadian control and may be responsible for generating
amplitudes of the circadian UV-resistance rhythms. We also found that the antioxidants involved were
different for UV-C resistance rhythms. However, no evident relationship between the effects of antioxidants
on UV resistance and their antioxidative potential was observed.
Originality / Value : The study shows that the chemical properties of the antioxidants, rather than their
general potencies, are responsible for generating the amplitudes of circadian UV-resistance rhythms.
