Observations on the functioning of the contractile vacuole of Dictyostelium discoideum with the electron microscope

Abstract

A study of pinocytosis in Dictyostelium discoideum using HRP as tracer material has shown that the contractile vacuole (CV) receives horseradish peroxidase (HRP) and has given information on the functioning of the CV. The quantitative analysis of the penetration of HRP has led to the following conclusions. Once the CV has expulsed its content, small vacuoles start to form. They progressively merge to form a main vacuole which finally bulges at the cell surface, expels its content through a pore, and flattens against the membrane, while the pore seals very quickly. The cycle then resumes. This study also shows that the small vacuoles coalescing with the main vacuole are generally functional. Therefore, the fact that alkaline phosphatase was not observed in these vacuoles (Quiviger, B., de Chastellier, C., and Ryter, A., 1978, J. Ultrastruct. Res. 62, 228–236) is not due to a nonfunctional state but rather to a different role in ion transport.