Mycosphere Essays 3. Myxomycete spore and amoeboflagellate biology: a review

Abstract

The spore and amoeboflagellate stages of the heterothallic myxomycete life cycle are generally a uninucleate haploid alternative to the multinucleate diploid plasmodial stage. The spore is produced in a sporangium which develops from the plasmodium, and is a dispersal and resistant stage which has ornamentations that can be used in taxonomy. These small spores have thick pigmented walls and are generally wind dispersed and require water and other biological and physical conditions in order to germinate; this dispersal can occur over long distances and the germination conditions apparently vary between and within a species. The amoeboflagellate stage has three alternative phases: myxamoeba, swarm cell and cyst. The myxamoeba is a typical pleomorphic amoeboid cell that is the major phase, since it is the vegetative phase that ingests bacteria and yeasts, and divides mitotically to form a clonal population of cells. The myxamoeba of heterothallic strains can also, after reaching a certain cell density, become sexually competent and fuse to produce the plasmodial stage. The swarm cell phase develops from the myxamoebal stage when free water is present; it also feeds on bacteria but does not divide unless it reconverts to the myxamoebal phase. The cyst phase develops from the myxamoebal stage, when growth conditions become adverse, by the condensing of the cell and the formation of a resistant wall.