Cell surface changes during the differentiation of Dictyostelium discoideum : Interaction of cells with Concanavalin A

The parameters affecting the agglutination of cells of Dictyostelium discoideum by Concanavalin A (ConA) have been investigated. Under the incubation conditions employed, incubation time does not markedly affect agglutination, but there are distinct optima for cell density and gyration speed. Agglutination does not occur at low temperatures, but the transition temperature between the unagglutinated and fully agglutinated states is markedly influenced by ConA concentration. The rate of aggregation of strain NC-4 is considerably reduced by ConA. In contrast, the differentiation of strain Ax-2 in the presence of ConA is either unaffected or only slightly inhibited, depending on the incubation conditions. Succinylated-ConA binds to the same sites as the unmodified lectin, but has no effect on the differentiation of strain NC-4, suggesting that ConA binding sites are not directly involved in cell-cell contacts vital to the differentiation of D. discoideum. There is a gradual decrease in the susceptibility of cells of D. discoideum to agglutination by ConA as the cells pass from exponential growth phase to stationary growth phase in axenic medium and from vegetative amoebae to aggregates on a solid substratum. These results provide quantitative evidence for a gradual change in carbohydrate containing binding sites during differentiation.