Changes in Surface Properties of Developing Zoospores of Blastocladiella entersonii: Binding of Concanavalin A

Binding of concanavalin A to the cell surface of developing Blastocladiella emersonii zoospores was explored by fluorescence microscopy, electron microscopy and radioactive labelling. After labelling with fluorescein isothiocyanate-conjugated concanavalin A, the fluorescence intensity of individual non-induced zoospores varied greatly. On the other hand, similarly labelled zoospores, induced with K+ ions for synchronous development, revealed a more even distribution of fluorescence intensity. The zoospore surface contained 4·3 × 107 concanavalin A binding sites per cell which were randomly distributed and closely attached to the surface. The affinity constants ranged from 7.5 × 107 m −1 to 3·5 × 105 m −1, while the Scatchard plot was typical of heterogeneous binding. Further developed cells, round cells and germlings contained 3.0 × 107 to 2·1 × 107 concanavalin A binding sites per cell which were mostly loosely associated patches protruding into the extracellular region. The affinity constants decreased appreciably compared with those measured at the zoospore stage. Specific concanavalin A binding characteristics appeared to correlate with the respective developmental stage of the zoospore.