Intracellular binding of wheat germ agglutinin by Golgi complexes, phagosomes, and lysosomes of Paramecium multimicronucleatum

Abstract

The compartments of the Paramecium digestive system were investigated with wheat germ agglutinin (WGA). By use of cryosectioning or Lowicryl K4M embedding combined with pulse-chase studies and WGA-gold labeling, WGA binding sites were located on membranes of the phagosome-lysosome system, including all four stages of digestive vacuoles, the discoidal vesicles, acidosomes, and lysosomes. In addition, the contents of lysosomes, cisternae at the trans face of Golgi stacks, and coated and uncoated blebs and vesicles at the putative trans Golgi network bind to WGA. Crystal-containing vacuoles characteristic of mid-log to stationary-phase cultures are enclosed by heavily labeled membranes. Alveoli underlying the plasma membrane sometimes contain binding sites, particularly on their outer membranes. Ciliary membranes previously shown to be labeled with WGA-FITC are negative in frozen thin and Lowicryl K4M sections. The presence of WGA binding sites on the trans face of the Golgi stack is the first indication in ciliated protozoa, such as Paramecium, of probable Golgi complex involvement in glycosylation similar to that in higher organisms. WGA-labeled coated vesicles in the endoplasm apparently lose their coats and coalesce to form lysosomes. Our study shows that WGA can be used as a specific intracellular marker of all digestive system membranes and of lysosomal content. These results support and extend our published scheme of membrane flow and recycling in Paramecium by providing another means of demonstrating membrane relationships.