Synchronization and signal transmission in protoplasmic strands of Physarum : Effects of externally applied substances and mechanical influences.

The phenomenon of synchronization of contraction rhythms was investigated on isolated protoplasmic strands of Physarum polycephalum. The strands were mounted as (gymnastic) trapezes; the contraction activities of the arms were measured independently under isometric conditions; and the connecting middle part of the arms was treated in different ways to block the signal transmission between the arms. Experiments for testing the influence of different chemicals on signal transmission demonstrated that whenever a substance blocked signal transmission it also disturbed the normal oscillatory contraction activity of a single strand, the endoplasmic streaming, and the normal architecture of the strand. No substance inhibited the transmission of the synchronizing factor specifically. As a depolarizing medium, 70 mM KCl solution did not hinder phase synchronization. On the other hand, compression of the middle part with a glass needle immediately led to dissynchronization as soon as the endoplasmic flow could not pass the point of constriction. Gelation of the endoplasm by a vibrating glass needle placed at the surface of the middle part had the same effect. It is concluded that a bioelectric continuance of the plasmalemma is not sufficient for signal transmission. In contrast, an intact endoplasmic flow appears to be obligatory. According to the experimental data presented, an electrical coupling responsible for phase synchronization between the two arms seems to be unlikely. The unknown synchronizing factor is transported via endoplasmic flow, i.e., the endoplasmic stream seems to present the pacemaker of the oscillatory contraction activity.