Distribution of the receptors for concanavalin A on the surface of Euglena gracilis as revealed by fluorescence microscopy

Abstract

The binding of concanavalin A (Con A) to the cell surface of Euglena gracilis was explored in various conditions by fluorescence microscopy. In both living and glutaraldehyde-fixed cells, the membrane of the emergent flagellum and of the reservoir are intensely and uniformly labelled by the fluorescein isothiocyanate-conjugated lectin. In contrast, the pellicular surface shows an alternation of reactive and unreactive strips. The streaks of binding, weak in brightness, pass helically around the cell body, probably at the level of the grooves and/or of the posterior margin of each ridge. Neither temperature variations nor exposure to the fluoresceinated ligand over a 30-min period consistently modify the binding pattern which in all experimental conditions occurs almost immediately at the flagellum level and subsequently at the reservoir and pellicle surface. Two main indications arise from the results: (i) concanavalin A receptors are especially localized in membrane areas possessing an unstable structure and numerous external glycosylated components; (ii) the distribution pattern of the lectin along the pellicle is similar to that known for the antipellicular antibodies.