PATTERNS OF OSCILLATION DURING MITOSIS IN PLASMODIA OF PHYSARUM-POLYCEPHALUM

The rhythmic contraction pattern in plasmodia of Physarum polycephalum was studied to determine whether characteristic changes occur during the synchronized nuclear division. An electrical method that measures the contraction rhythm in situ during several cell cycles was used. Bi opsies of the plasmodia were taken at 17 min intervals for precise det ermination of the cell cycle stages and were correlated with the simul taneously measured contraction rhythm. All measurements were performed in a temperature controlled environment (27 degrees C) at 100% relati ve humidity with the plasmodia (less than 24 h old) growing on a semi- defined agar medium. A total of 14 different plasmodia have been exami ned, and on one occasion the plasmodium was followed through 3 subsequ ent mitoses. The mitotic stages were identified with aceto-orcein colo ring techniques and by fluorescence methods. Except for a few cases wh ere a mitotic asynchrony of 2-3 min was observed, the mitotic events o ccurred simultaneously in the nuclei within a single plasmodium. Both the occurrence of the first mitosis after inoculation and the intermit otic times were highly variable. Our study indicates that the contract ion rhythm in plasmodia of Physarum is unperturbed during the synchron ized nuclear division. However, in 5 of the 17 examined mitoses an amp litude decay was observed. We discuss possible explanations for the ob tained results with emphasis on the applied techniques, interpretation of the oscillation patterns, and possible restrictions in the cell it self.