CYTOPLASM RESCUES AN ARRHYTHMIC MUTANT ON THE CIRCADIAN-RHYTHM OF MATING REACTIVITY IN PARAMECIUM-BURSARIA

Cells of an unusual Paramecium bursaria stock (Sj2) expressed rhythmic mating reactivity in a light/dark cycle (LD) and under continuous ill umination (LL). When placed in continuous darkness (DD), did not show rhythmicity but rather demonstrated a continuous high mating reactivit y. However, mating reactivity was reduced following exposure to a 6-h light pulse interrupting the DD, and then recovered to its former cond ition. Genetic analysis showed the arrhythmicity in DD to be a dominan t character inherited in a Mendelian ratio. On the other hand, a clone (MClw) that did not show the rhythmicity in either DD or LL was isola ted from the parent stock Sj2w following a 5-h treatment with 2 mu g/m l nitrosoguanidine (MNNG). The MClw cells expressed weak rhythmicity i n LD, but were insensitive to a 6-h light pulse in DD. The arrhythmici ty in LL was inherited cytoplasmically. In addition to this, rhythmici ty in LL could be recovered by injection of cytoplasm from the wild-ty pe cell when the recipient cell was homozygous for the wild-type nucle ar gene (+/+). The cytoplasmic components or factors are assumed to co ntrol the functional circadian system and genetically determine the rh ythmicity of mating reactivity.