Abstract
Using low temperature and colchicine, we examined how axopodia play a role in the initiation and subsequent process of cell fusion in a large heliozoan Echinosphaerium nucleofilum (strain MA). Although the fusion reaction is naturally temperature-dependent, preliminary treatment with a low temperature (2°C) induced the reaction more efficiently than in the control kept at room temperature (20°C). During the recovery process from the cold, the reaction was enhanced conspicuously in the presence of colchicine; the fusion indices were 2.05 to 5.68 after a 9 h incubation with 4 to 8 mM colchicine. When treated with 4 to 10 mM colchicine without the preliminary cold treatment, the reaction also was enhanced. This means that the reaction depended upon the colchicine concentration and resulted in partial or complete degradation of axopodia; fusion indices were 1.08 to 3.77 after a 9 h incubation with 4 to 10 mM colchicine. We discuss these results and the electron-microscopical data, in relation to the role of axopodia in the fusion reaction.
