Oxidative Damages and Repair in Euglena gracilis Exposed to Ozone II. Membrane Permeability and Uptake of Metabolites

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Significant injuries to the plasma membrane were detected in Euglena gracilis cells during ozone exposure (240 μl・liter^<-1>, delivery rate of 1 μmol・min^<-1>), as assessed by measuring the alterations of vitamin B_<12> and acetate uptakes and the leakage of intracellular K^+ (Rb^+). A rapid decrease in the uptake of vitamin B_<12> and acetate was observed within 15 min of treatment, indicating that both transport systems are very sensitive to O_3. On the other hand, the leakage of intracellular K^+ ions, as measured by the efflux of ^<86>Rb^+ from prelabelled cells, could only be detected after 30 min of O_3 exposure. These results suggest that the initial metabolic symptoms of injury is at the level of the two transport systems examined and that the alteration of the membrane permeability to K^+ ions appears as a second step in the cascade of oxidative events at the plasma membrane level. When Euglena cells were allowed to recover under autotrophic growth conditions following O_3 treatment, vitamin B_<12> and ^<86>Rb^+ (K^+) ions uptakes returned gradually to control level within 5 h of the recovery period. Acetate uptake returned to control level at a slower rate and needed 20 h for complete recovery. These results indicate that the cells were able to actively repair most of the initial oxidative damages induced by O_3. The metabolic significance of the repair mechanism(s) is discussed.
日本植物生理学会の論文