UV-B light induces an adaptive response to UV-C exposure via photoreactivation activity in Euglena gracilis

Abstract

Phytoplankton such as Euglena are constantly exposed to solar light which is used for photosynthesis. Although the solar ultraviolet (UV) induces DNA damage such as cyclobutane-pyrimidine dimers (CPDs), many kinds of living organisms can repair CPDs by photoreactivation (PR) utilizing the near-UV/blue light component in sunlight. Euglena cells are known to possess such PR activity. In the present paper, the formation of CPDs induced by UV-C exposure and the photoreactivation PR repair of these CPDs by UV-A are demonstrated. To clarify the adaptive responses prior UV-B irradiation on PR activity, cells were cultured in the dark or under UV-B light. When the cells were cultured in the dark for 3 d prior to UV-C exposure, PR activity decreased. When the cells were cultured under UV-B light, however, PR activity increased. These results suggest that exposing the cells to UV-B prior to exposure to UV-C induced an adaptive response towards DNA damage caused by UV-C exposure, and this UV-C induced damage was repaired through PR activity.

Metabolic Responses of a Model Green Microalga Euglena gracilis to Different Environmental Stresses

“…Euglena is highly adaptable to changing environments, some adverse stresses like UVB (Takahashi et al, 2006 ), heavy metals (Moreno-Sánchez et al, 2017 ), and antibiotics (Ebringer, 1964 ). In this study, microalgal cells showed tolerance to antibiotics, PRM, without significant cell growth inhibition, chlorophyll reduction, and paramylon and lipid alterations.…”

Use of O-J-I-P Chlorophyll Fluorescence Transients to Probe Multiple Effects of UV-C Radiation on the Photosynthetic Apparatus of Euglena

“…The effect of UV radiation on photosynthetic organisms has been extensively investigated over the past decades due to the depletion of ozone layer. Many studies have analyzed the effect on UV radiation on photosynthetic organisms and observed that UV radiation causes serious damages to photosynthetic apparatus thus, induced a decrease of the photosynthetic capacity (Prasad and Zeeshan (2004), Holzinger and Lutz (2005) and Takahashi et al (2006)). …”

Adaptive response: some underlying mechanisms and open questions

“…The magnitude of the AR has been shown to increase with the dose of radiation up to a certain threshold (Bryant, 1976). A specific dose of UVB was required to induce AR in Euglena (Takahashi et al, 2006). Induction of AR by methylating agents has been reported in eukaryotic cells as well.…”

“…It has been proposed that these effects could be related to the induction of an AR. The AR induced by conditioning UVB exposures in Euglena may not be due to biosynthetic UV-absorbing compounds, but to the induction of photolyase enzymes (Takahashi et al, 2006). Activation of UVB-induced AR in human skin cells could involve a p53-dependent gene program with p53-induced cell cycle arrest and DNA repair (Decraene et al, 2005).…”