Oscillating contractions in protoplasmic strands ofPhysarum:stretch‐induced phase shifts and their synchronization

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Abstract
Isolated protoplasmic strands from plasmodia of the acellular slime mold Physarum polycephalum reveal spontaneous contraction rhythms with an average period of 2.1 min at room temperature and high relative humidity. Stimulation produced by stretching the strands to one half their original length (50%) results in a phase shift of the contraction‐relaxation cycles. The duration of the stress‐relaxation with an average value of 43.7 sec is dependent upon the time of stretch stimulus relative to the phase of the spontaneous contraction‐relaxation cycle. As can be seen in protoplasmic strands in which only one half of the strand is stretched, the induced phase difference disappears again when the phase‐shifted portion of the strand remains in contact with the experimentally unaffected region. The reasons for the experimentally induced phase shift and the regulation of phase coordination are discussed in relation to the biochemical oscillation processes governing the cycling contraction phenomena.