Variations in the biological clock of the slime moldPhysarum polycephalummeasured electrically

Abstract

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.

A novel electrical method to study plasmodial contractions in Physarum. Synchrony and temperature dependence

“…By inspecting the curves it is clear that the data points from different experiments are somewhat scattered, especially at low temperatures. Taking into consideration that the individual Physarum rhythms initially are not exactly equal, together with the spontaneous deviations in the period that often occur in long time series (Halvorsrud et al, 1993), this is to be expected and it is clear that the Physarum specimens respond similarly to temperature changes.…”

“…Keese (1984, 1986, 1989, 1991) developed a method for studying the dynamic morphology of cells electrically by culturing the cells on small gold electrodes. This method has been adapted for measurements of the rhythmical behavior of Physarum polycephalum (Halvorsrud et al, 1993). One disadvantage of this system is the lack of ability to cope with migrating plasmodia.…”