Summary: Exponential phase cells of treated with the superoxide free-radical generating agent menadione (MD; 0·2 mM) for 60 min adapted to become resistant to the lethal effects of a higher concentration of MD (4 mM). Inhibition of protein synthesis by treatment with cycloheximide totally prevented the adaptation to MD, indicating that this is an inducible response completely dependent on protein synthesis; this differs from the situation with peroxide in which only some of the adaptive response is cycloheximide-sensitive. Cells subjected to heat shock (23 to 37 °C) or treatment with hydrogen peroxide (HO; 0·2 mM, 60 min) became more resistant to 4 mM-MD; however, MD pretreatment did not induce any thermotolerance or resistance to peroxide. These differences between the response to MD and HO were reflected in the results of L-[S]methionine labelling studies. Using one-dimensional electrophoresis, only one polypeptide (60 kDa) was seen to be induced by 0·2 mM–MD and this was also induced by heat shock but not peroxide stress. With heat shock or peroxide treatment the induction of at least 10 polypeptides was detected using this approach. Using an isogenic petite strain, it was found that functional mitochondria were needed for conferring full resistance to MD, but that induction of the adaptive response was not dependent on mitochondrial function.


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