Synchronization and signal transmission in protoplasmic strands ofPhysarum : Reaction to varying temperature gradients.

Isolated protoplasmic strands ofPhysarum polycephalum, mounted as a trapeze, show synchronous contraction activities when the isometric tension development of both arms of the trapeze is measured independently of each other. This phase regulation can be experimentally disturbed by temperature changes. Within a permanent gradient, however, the phases become resynchronized. The maximal temperature gradient between both arms allowing a phase resynchronization was approximately 9° C along a distance of 25 mm. The transmission of the signal along the middle piece of the trapeze (which, as the connecting part of both arms, is responsible for signal transmission in phase synchronization) can be influenced by temperature changes. The minimal temperature allowing a signal transmission is 15° C, the maximal temperature approximately 29° C. A morphological investigation of protoplasmic strands mounted as trapezes revealed that the normal architecture of the objects is not influenced by the experimental trapeze arrangement. Permanent thermal gradients induce thermotactic reactions, i.e., a preferred protoplasmic mass transport into one arm of the trapeze. This leads, after several hours, to a morphological asymmetry of the trapeze. In spite of the fact that this reaction limits the temporal use of trapezes within thermal gradients to 2-3 h, the capacity of such strands for phase regulation is not hindered. Thermal gradients are suitable methods for studying the unknown phase-regulating factor and its transmission. As criteria for an intact pathway of signal transmission, the capacity of the trapeze arms to resynchronize as well as to maintain synchronization within a thermal gradient can be used.