[Effect of actinomycin D on salinity acclimation of Paramecium calkinsi (Ciliophora, Peniculia)].

Salinity acclimation of euryhaline ciliate Paramecium calkinsi evaluated by swimming velocity was over in 4-5 days. In two series of the main experiment, the acclimation was over in two and three days when actinomycin D (an inhibitor of DNA-dependent RNA polymerase) was added after various periods of the ciliate incubation at a changed salinity (0, 3, 6, and 24 h). The obtained data indicate that the inhibiting effect of actinomycin D on salinity acclimation of P. calkinsi is manifested only within the first day of the ciliate incubation in an altered environment; by the end of this period their swimming velocity was similar to the control one (acclimation in the absence of the inhibitor). Thus, expression of genes associated with salinity acclimation in paramecium largely completes within the first day, while the acclimation continues for at least 4-5 days. We propose that the acclimation-competent species possess a correspondingly rich genetic program.