Analysis of Microfilament Organization and Contractile Activities in Physarum

Abstract

Publisher Summary This chapter presents the analysis of microfilament organization and contractile activities in the acellular slime mold Physarum polycephalum. Physarum was predominantly used to analyze the morphology and contraction physiology of the cytoplasmic actomyosin system as exemplifying the situation in nonmuscle cells. During the vegetative phase, Physarum forms large motile phaneroplasmodia that can grow up to several square meters. Due to the large variety of the different life cycle and experimentally derived stages of Physarum, microfilaments can attain manifold manifestations ranging from a primitive actomyosin cortex beneath the plasma membrane in amoeboflagellates to an extremely complex arrangement of actomyosin fibrils extending through the entire cytoplasmic matrix in vegetative phaneroplasmodia. Most significant is the existence of the cortical microfilament system, which shows a common and permanent cytoskeletal differentiation in all investigated growth forms. The microfilament system serves two main functions. Together with the spectrin-like membrane skeleton, the actomyosin cortex stabilizes the cell surface and participates in morphogenetic events such as formation of an invagination system. The actomyosin cortex delivers motive force by regular contractile activities, which are transformed via the plasma membrane into hydraulic pressure gradients and finally result in protoplasmic streaming via gel-sol transformations.