TRICHOCYST MEMBRANE FATE IN LIVING PARAMECIUM-PRIMAURELIA VISUALIZED BY MULTIMODAL CONFOCAL IMAGING

Trichocysts are secretory organelles located at the surface of several ciliates, docked at the plasma membrane, Their secretion is similar t o other exocytic processes: the trichocyst membrane fuses with the pla sma membrane, its content is released outside the cell, and the membra ne is retrieved back into the cell, The fate of the trichocyst membran e in living Paramecium primaurelia was investigated by inducing massiv e synchronous exocytosis in the presence of fluorescein isothiocyanate -conjugated lectins or of cationized ferritin. The marker is trapped w ithin the retrieved trichocyst membrane sac, and many regularly spaced , fluorescent ghosts are formed, As time proceeds, the number of label ed ghosts decreases, and few fluorescent vacuoles appear within the ce ll, The relationship between trichocyst ghosts and the vesicles of the phagosome-lysosome system was examined by labeling cells with Texas R ed-conjugated bovine serum albumin, a fluorescent marker for phagocyto sis, Starting from two confocal images of the same cell labeled with t he two fluorescent probes, a new single image was generated by associa ting each image with a different red or green value, This multimodal a nalysis showed that trichocyst ghosts fuse with secondary lysosomes or are incorporated into digestive vacuoles. The vacuolar content is deg raded and fluorescence is then found in the vesicles of the phagosome- lysosome system, and, at last, in small weakly labeled vesicles locate d on the cell surface.