Oxidative Damages and Repair in Euglena gracilis Exposed to Ozone. I. SH Groups and Lipids

Malondialdehyde, a product of lipid oxidation, increased gradually when Euglena gracilis cells were bubbled with 240 μ1.liter−1 ozone (delivery rate of 1μmolO3.min−1) for 120 min. Simultaneously, the sulfhydryl group content decreased by 36% during the treatment, which was mainly due to oxidation of protein sulfhydryl groups. The molar amount of SH groups oxidized was 3 times higher than that of fatty acid oxidized, indicating that sulfhydryl groups were more accessible or more easily oxidized by O3 than fatty acids. When Euglena cells were allowed to recover under autotrophic growth conditions following O3 treatment, viable cells were incapable of dividing during the first 5 h of the recovery period but regenerated SH groups nearly to the control level. The increase of SH content during this period preceded the resumption of cell division and the restoration of normal growth. These results suggest that the regeneration of SH groups by Euglena cells is a part of a mechanism involved in the repair of oxidative damage caused by ozone and is an essential step for the initiation of cell division.