On the Cycle of the Water Expulsion Vesicle in the Ciliate Tetrahymena pyriformis

Abstract

Cinematography and ultrastructural studies were made on the cyclic function of the water expulsion vesicle (contractile vacuole) and its related struc- tures in Tetrahymena pyriformis. The water expulsion vesicle of Tetrahymena has several main collecting tubules which are repeatedly used from one cycle to the next. During the early part of evacuation, water in the vesicle flows back into the main collecting tubules forming recognizable ampullae. The vesicle then moves toward one of the two outlet pores, and a system of microtubules which anchor the vesicle to the pore helps exert radial tension on the outlet pore membrane. Rupture of this membrane results in both rapid evacuation of the vesicle and its invagination and collapse. No evidence was found for active contraction of the vesicle or its membranes. Water expulsion vesicles (commonly called contractile vacuoles) are found in almost all freshwater protozoa. Apparently, the water expulsion vesicle serves primarily as an osmoregulatory organelle; however, it may also serve as an excretory organelle (Kitching, 1956). The structural complexity of the expulsion vesicle varies from the simple roving type as described in Ameba (Pappas & Brandt, 1958; Wigg et al., 1967) to the complex fixed type with its elaborate network of nephridial tubules, ampullae, and related structures as described in Paramecium (Schneider, 1960). The ultrastructural complexity of the water expulsion vesicle of Tetrahymena, as described by Elliott & Bak (1964), is intermediate between these two extremes. Elliott & Bak found that the water expulsion vesicle of Tetrahymena communicates with a network of nephridial tubules similar in many respects to that of Paramecium, but they did not describe ampullae or a system of main collecting canals. Although ultrastructural descriptions of the water expulsion vesicle and its related structures are helpful in determining functional events, it is only by observations on living organisms that we can get a continuous and reliable series of stages in the cyclic functional events of this organelle. The present cinematography and ultrastructural observations add to our information on ABSTRACT: Cinematography and ultrastructural studies were made on the cyclic function of the water expulsion vesicle (contractile vacuole) and its related struc- tures in Tetrahymena pyriformis. The water expulsion vesicle of Tetrahymena has several main collecting tubules which are repeatedly used from one cycle to the next. During the early part of evacuation, water in the vesicle flows back into the main collecting tubules forming recognizable ampullae. The vesicle then moves toward one of the two outlet pores, and a system of microtubules which anchor the vesicle to the pore helps exert radial tension on the outlet pore membrane. Rupture of this membrane results in both rapid evacuation of the vesicle and its invagination and collapse. No evidence was found for active contraction of the vesicle or its membranes. Water expulsion vesicles (commonly called contractile vacuoles) are found in almost all freshwater protozoa. Apparently, the water expulsion vesicle serves primarily as an osmoregulatory organelle; however, it may also serve as an excretory organelle (Kitching, 1956). The structural complexity of the expulsion vesicle varies from the simple roving type as described in Ameba (Pappas & Brandt, 1958; Wigg et al., 1967) to the complex fixed type with its elaborate network of nephridial tubules, ampullae, and related structures as described in Paramecium (Schneider, 1960). The ultrastructural complexity of the water expulsion vesicle of Tetrahymena, as described by Elliott & Bak (1964), is intermediate between these two extremes. Elliott & Bak found that the water expulsion vesicle of Tetrahymena communicates with a network of nephridial tubules similar in many respects to that of Paramecium, but they did not describe ampullae or a system of main collecting canals. Although ultrastructural descriptions of the water expulsion vesicle and its related structures are helpful in determining functional events, it is only by observations on living organisms that we can get a continuous and reliable series of stages in the cyclic functional events of this organelle. The present cinematography and ultrastructural observations add to our information on