EPIXENOSOMES PECULIAR EPIBIONTS OF THE PROTOZOAN CILIATE EUPLOTIDIUM-ITOI - DO THEIR CYTOPLASMIC TUBULES CONSIST OF TUBULIN

Epixenosomes, epibiontic organisms living on the protozoon ciliate Eup lotidium itoi, like prokaryotes,lack a true nucleus surrounded by a nu clear envelope. However, their cytoplasm, at least in the mature state , is somehow compartmentalized by the presence of a complex extrusive apparatus surrounded by a form of basket consisting of bundles of tubu les (BT), 20-24 nm in diameter, delineated by a wall made of globular subunits. The nature of these tubules was investigated by means of in vivo experiments, ultrastructural analysis and immunocytochemistry by both fluorescence and electron microscopy. It has been found that BT, besides being well preserved when fixed in the presence of tannic acid , are sensitive to factors known to depolymerize cytoplasmic microtubu les in a variety of cells such as nocodazole and cold and show a posit ive immunoreaction against different antitubulin antibodies. On the ba sis of all the results obtained, the hypothesis that the epixenosomal BT consist of tubulin acquires a strong credibility. This is particula rly interesting if we consider that tubulin in prokaryotes has never b een conclusively demonstrated.