RHYTHMICITY IN T H E PROTOPLASMIC STREAMING OF A SLIME MOLD, PHYSARUM POLYCEPHALUM* I. A STATISTICAL ANALYSIS OF -l~v: ELECTRIC POTENTIAL RHYTHM

The electric potential difference (1 to 15 inv.) between two loci of the slime mold connected with a strand of protoplasm changes rhythmically with the same period (60 to 180 seconds) as that of the back and forth protoplasmic streaming along the strand. Generally some phase difference is observed between them. Periods of the electric potential rhythm show a Gaussian distribution. Amplitudes give a somewhat different distribution curve. Wave forms are not always simple Imrmonic ones, but are distorted more or less. However, auto-correlation analysis proves that there is s dominant rhythm of a nearly constant period which coincides with the mean period of the Gaussisn distribution curve. Calculations made on an assumption that the electric potential rhythm is the result of many elementary rhythms (i.e., same periodicity, arbitrary phase angles) distributed throughout the plasmodinm, give s satisfactory coincidence with the observed distribution for the amplitude. The predominance of a rhythm of a nearly constant periodicity suggests the existence of well organized interactions among components of a contractile protein network, the rhythmic deformation of which is supposed to be responsible for the protoplasmic streaming and for the electric potential rhythm. One of the most characteristic properties of the plasmodium of the slime mold, Physarura polycephalura, is that it shows a remarkable back and forth protoplasmic streaming along a protoplasmic strand. Because of this typical pattern of protoplasmic streaming, as well as its large size and ease of culturing, the slime mold can be used as good material in studying the mechanism of protoplasmic streaming. Many interesting studies have been published recently on the biophysics and biochemistry of this organism. The electric potential difference between two loci of the slime mold connected with a strand of protoplasm changes rhythmically with the same period as that of the back and forth protoplasmic streaming along the strand (Kamiya and Abe, 1950). The rhythmic change in the potential occurs whether * Supported by a Grant for Fundamental Scientific Research from the Ministry of Education.