VARIATIONS IN THE BIOLOGICAL CLOCK OF THE SLIME-MOLD PHYSARUM-POLYCEPHALUM MEASURED ELECTRICALLY

In the plasmodial stage the slime mold Physarum polycephalum exhibits oscillatory phenomena. The ectoplasm contracts regularly, resulting in oscillatory (shuttle) streaming of the endoplasm. This periodic phenomenon represents a biological clock that is not well understood. We have studied quantitatively the stability of the rhythmic contractions in Physarum over long intervals of time using an electrical method that permits in situ measurements of the undisturbed plasmodium. The measured resistance curves were analyzed with fast Fourier transform, and the power spectra revealed one fundamental frequency with several higher harmonics. The period determined from the fundamental frequency (typically 1.8 minutes) was quite stable over 40 hours at defined temperature, humidity and growth conditions, but deviations by a factor of 2 occurred on shorter time scales. The period of the different Physarum specimens varied from 1 to 6 minutes at room temperature.