SECRETION OF SLIME, THE EXTRACELLULAR-MATRIX OF THE PLASMODIUM, AS VISUALIZED WITH A FLUORESCENT-PROBE AND ITS CORRELATION WITH LOCOMOTION ON THE SUBSTRATUM

Slime, the extracellular matrix of Physarum plasmodium, is secreted by the exocytosis of a vesicles that contain a slime precursor. Using an antibody raised against biochemically purified slime, we detected the intracellular localization of the slime vesicle. Slime vesicles are a bundant in the advancing front of the plasmodium, as confirmed by elec tron microscopic observation in two different cross-sectional angles. Screening various reagents, we found that rhodamine-phosphatidylethano lamine (Rh-PE) binds specifically to slime in both its intravesicular and extracellular forms, as confirmed by immunoelectron microscopy usi ng an antibody against fluorochrome rhodamine. The plasmodia vitally s tained with Rh-PE exhibited dynamic fluorescent patterns during the co urse of locomotion. The fluorescence was conspicuous at the periphery of the leading pseudopods and oscillated according to the shuttle stre aming that accompanied the relaxation and contraction of the periphery ; it was intense in the relaxation phase when pseudopods extended, and became weak in the contraction phase when pseudopods contracted. The results collectively mean that the slime vesicles carried by the cytop lasmic streaming accumulated prior to secretion at the advancing margi n of the plasmodium.