PHASE SWITCHING OF OSCILLATORY CONTRACTION IN RELATION TO THE REGULATION OF AMEBOID BEHAVIOR BY THE PLASMODIUM OF PHYSARUM-POLYCEPHALUM

The plasmodium of the true slime mould Physarum polycephalum is a larg e aggregate of protoplasm and behaves like an amoeboid cell, exhibitin g rhythmic contraction everywhere within the organism. Phase dynamics of these oscillations were studied in relation to the global organizat ion of amoeboid behavior, by analysing the thickness oscillation, isot onic tension and the motive force of the streaming. Usually the plasmo dium showed synchrony, the phase of the oscillation being the same eve rywhere excepting the peripheral part. We found several situations whe re this in-phase relationship switched to anti-phase. This occurred ei ther at the early stages of the plasmodial coalescence, or when a sing le plasmodium was nearly separated by partition, or when the streaming of the protoplasm was hindered by applying the hydrostatic pressure. Furthermore, the motive force of the protoplasmic streaming increased once the anti-phase relationship was established. In this way, the wea k interactions among plasmodial parts induce the switching of phase re lationship from in-phase to anti-phase, and this transition in turn ac ts to increase the interaction by promoting a rapid mixing of the prot oplasm. This global feedback mechanism by phase switching should help maintain a large single plasmodium without separating into parts. The possible mechanism of phase switching is discussed in terms of coupled nonlinear oscillators. (C) 1996 Academic Press Limited.