Dynamic aspects of the contractile system in Physarum Plasmodium: I. Changes in spatial organization of the cytoplasmic fibrils according to the contraction‐relaxation cycle

Abstract

AbstractDynamic changes in the spatial organizations of cytoplasmic fibrils (microfilament bundles) related to the contraction‐relaxation cycle in thin‐spread plasmodia of Physarum polycephalum were investigated by fluorescence microscopy, where NBD‐phallacidin was used to stain the fibrils, combined with polarizing light microscopy.The fibrillar organization in the anterior region, which consists of a fanlike spreading plasmodial sheet, strikingly changed according to the phase of the cycle. In the early stage of the contraction, as the endoplasm began to stream backward, the fibrils developed into a number of slender and flabby fibrils emanating from the inside of the cell membrane and the nodes. They became thicker and more straightforward fibrils running parallel to each other at the middle stage, and finally formed a thick framework consisting of a “polygonal network” near the tip of the migrating front and a “parallel array” in the inner part. In the relaxation phase, as the endoplasm streamed forward, the fibrillar framework disintegrated gradually and finally disappeared almost completely, remaining only around the nodes in some cases.The fibrillar patterns in the posterior region, which consists of ramified strands, showed no conspicuous rhythmic change with alternation of the streaming direction.