Immunocytochemistry of the acellular slime mold Physarum polycephalum. V. Cryosectioning now allows analysis of non-extracted plasmodia of any and all stages.

The spatial distribution of cytoplasmic actin in endoplasmic drops as well as in plasmodial strands can be demonstrated in cryosections by fluorescently labelled phallotoxins and actin antibodies. Our results on cryosections show an identical fibrillar actin distribution as revealed in semithin sections after conventional fixation and embedding. Thus, it is now possible to apply immunocytochemical analysis to any and all plasmodial stages with or without prior fixation and without using extraction procedures. Consequentially the loss of soluble compounds during processing is avoided. The most protective pretreatment of the living specimens before freezing is a 15 min incubation in 1.5 M sucrose containing 50 mM KCl, 10 mM EGTA and 10 mM PIPES buffer, pH 7.0, at 4 degrees C.