Synchronization and signal transmission in protoplasmic strands of Physarum : The endoplasmic streaming as a pacemaker and the importance of phase deviations for the control of streaming reversal.

The importance of endoplasmic streaming in the synchronization of contraction activites in plasmodial strands of Physarum was investigated under experimental conditions allowing simultaneous observation of the endoplasmic flow in the middle part of a strand mounted as a trapeze and the measurement of isometric contraction activities of the arms of the trapeze, as well as of the activities of the strand portion connecting the arms. The correlation of longitudinal and radial contraction activities in different regions of a trapeze was examined. Whereas the arms and the middle part of a trapeze contract synchronously in a longitudinal direction (in-phase behaviour), an antiphase correlation appeared when comparing the longitudinal contraction activity of the arms and the radial activity of the middle part. This result is interpreted to mean that the middle part is able to perform isotonic contractions which induce radial dilatation of the strands. No clear-cut correlation between longitudinal and radial activities could be found when measuring simultaneously both activities in one and the same arm of a trapeze by combining tensiometry and cinematography. Protoplasmic shuttle streaming within a strand mounted as a trapeze is found to run regularly out of one arm through the middle part into the other arm, and vice versa. There is no correlation between the time points of streaming reversal and a certain stage of contraction cycles as presented by the contraction curves of the arms. However, there is a good correlation between the points of streaming reversal and the phase deviations of the longitudinal contraction activities of the arms. The importance of these phase deviations for the control of streaming reversal, i.e., for the generation of hydrostatic pressure differences in a system working with phase synchrony, is discussed. The role of endoplasmic streaming as a pacemaker for synchronization phenomena of contraction activities is stressed. The possibility is discussed that shuttle streaming of endoplasm acts as a mechanical coupling within the regulation phenomena resulting in spatial monorhythmicity.