RECOVERY IN STATIONARY-PHASE PARAMECIA FROM RADIATION EFFECTS LEADING TO MUTATION

Abstract

Paramecium aurelia cultures with less than 1% autogamy were irradiated. From each irradiated paramecium, 25 autogamous progeny were isolated 5-10 days after irradiation to detect lethal and other deleterious mutations. There was a continuous decrease in mutation with duration of postirradiation starvation. The paramecia were either 5 or 7 days old and no differences were found that could be attributed to this variation in preirradiation starvation. Irradiated stationary-phase animals transferred to culture media containing 1 mg/ml streptomycin or 0.5 mg/ml chloramphenicol showed a decreased amount of mutation. These studies indicate that loss of premutational damage can occur during the intermediate period after irradiation; the period in which modification can occur does not come to a sudden end when the paramecia are not growing; and the decrease in mutation by postirradiation treatment is primarily the consequence ot the increased time available for loss of premutational damage and , consequently, that the loss is a metabolic process.