Nakagaki T, Ueda T
Graduate School of Human Informatics, Nagoya University, Japan.
J Theor Biol. 1996 Apr 7;179(3):261-7. doi: 10.1006/jtbi.1996.0065.
The plasmodium of the true slime mould Physarum polycephalum is a large aggregate of protoplasm and behaves like an amoeboid cell, exhibiting rhythmic contraction everywhere within the organism. Phase dynamics of these oscillations were studied in relation to the global organization of amoeboid behavior, by analysing the thickness oscillation, isotonic tension and the motive force of the streaming. Usually the plasmodium showed synchrony, the phase of the oscillation being the same everywhere excepting the peripheral part. We found several situations where this in-phase relationship switched to anti-phase. This occurred either at the early stages of the plasmodial coalescence, or when a single 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 weak interactions among plasmodial parts induce the switching of phase relationship from in-phase to anti-phase, and this transition in turn acts to increase the interaction by promoting a rapid mixing of the protoplasm. 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.
多头绒泡菌这种真正的黏菌的原生质团是一大团原生质，其行为类似于变形虫细胞，在生物体的各个部位都表现出有节奏的收缩。通过分析厚度振荡、等张张力和原生质流动的驱动力，研究了这些振荡的相位动态与变形虫行为的整体组织之间的关系。通常情况下，原生质团表现出同步性，除了周边部分，振荡的相位在各处都是相同的。我们发现了几种这种同相关系转变为反相关系的情况。这要么发生在原生质团融合的早期阶段，要么发生在单个原生质团几乎被分隔开的时候，要么发生在通过施加静水压力阻碍原生质流动的时候。此外，一旦建立了反相关系，原生质流动的驱动力就会增加。这样，原生质团各部分之间的微弱相互作用会导致相位关系从同相转变为反相，而这种转变反过来又通过促进原生质的快速混合来增加相互作用。这种通过相位切换的全局反馈机制应该有助于维持一个大的单个原生质团而不分裂成多个部分。本文从耦合非线性振荡器的角度讨论了相位切换的可能机制。
