Studies on contraction rhythm of the plasmodial strand IV. Site of active oscillation in an advancing plasmodium

Summary

From the anterior region of an advancingPhysarum plasmodium, a slender rectangular piece of cytoplasmic gel was removed and its contractile properties were compared with those of a strand segment isolated from the network region of the same plasmodium. The anterior piece, in spite of injury caused by the surgical operation, began to contract and relax periodically without an appreciable lag stage after it had been excised. The segment of strand (vein) obtained from the network behind the advancing front showed no significant rhythm immediately after it had been isolated. Only after a lag period lasting for 10–20 minutes (stage I.Yoshimoto andKamiya 1978 a) did the strand gradually begin to oscillate under both isometric and isotonic conditions. Such behaviour of the isolated strand is interpreted as showing that the active site of the rhythmic contraction and relaxation in the advancing plasmodium is restricted to its anterior zone and the rear network structure plays no leading part in bringing about rhythmicity when it isin situ. Rhythmicity of a strand segment excised from the plasmodial network occurs only after it has been isolated as an independent system. Whether or not the strand is under tension is not important for this functional reorganization.