Spatio-temporal relationships between protoplasmic streaming and contraction activities in plasmodial veins of Physarum polycephalum.

Plasmodial veins of Physarum polycephalum were investigated by combining cinematographical, morphological, and tensiometrical techniques. Translucent and nontranslucent (thicker) strands remaining in their original position on filter paper were analyzed in respect to their radial contraction cycles and the resulting streaming activity of the endoplasm. A new technique for measuring the flow intensity by a microbalance method allowed testing of the influence of radial contraction on actual streaming processes within a strand. Stationary ectoplasm and flowing endoplasm are involved in a mutual transformation process: thereia an exchange of ectoplasm and endoplasm in the form of protoplasmic streamlets crossing the borderline between the endoplasmic stream and the ectoplasmic tube. Radial contraction cycles show the same time periodicity as the endoplasmic shuttle streaming. Relationships between radial contractions, streaming rates of endoplasm and streamlets between ectoplasm and endoplasm were analyzed. The participation of the ectoplasmic walls in motive force generation and their function in control of streaming throughput is discussed.