Oscillating contractions in protoplasmic strands of Physarum: simultaneous tensiometry of longitudinal and radial rhythms, periodicity analysis and temperature dependence.

1. The construction of a 'twin-tension transducer' allows the simultaneous measurement of the same or different contraction rhythms at any selected sites of living plasmodia of Physarum polycephalum. This method has been used to analyse the relation of longitudinal and radial contraction activity within migrating plasmodia and plasmodial veins, under isometric as well as under isotonic conditions of measurement. 2. A periodicity analysis of the oscillating contraction rhythms revealed average period values for the longitudinal contraction cycle of 2-1 min and for the radial contraction cycle of 1-3 min at a temperature of 22 degrees C. 3. The periods of longitudinal contraction depend on the environment of the strands. The mean value under submerged conditions was 2-9 min. 4. The temperature dependences for both longitudinal and radial contraction cycles were determined to provide reliable values for the normal reaction range of the contractile system (cytoplasmic actomyosin). The values for radial contraction activity are 2-0 min at 16 degrees C, 1-5 min at 20 degrees C, and 1-2 min at 24 degrees C. The range between 16 degrees and 24 degrees C can be regarded as physiological. 5. The possibility is discussed that only one 'genuine' contraction frequency of cytoplasmic actomyosin exists in Physarum.