pseudoplasmodium

Pseudoplasmodium is a transient, multicellular stage in the life cycles of certain cellular slime molds, most notably the dictyostelids such as Dictyostelium discoideum. It forms when starving social amoebae secrete and respond to chemoattractants like cyclic AMP, causing thousands to millions of individual cells to aggregate into a single, motile mass. Although called a pseudoplasmodium, it is not a true plasmodium; the structure comprises many separate cells held together by extracellular matrix rather than a single cytoplasm containing multiple nuclei.

During this stage, the cells reorganize into prestalk and prespore regions, establishing a body axis. The aggregate elongates and contracts, forming a slug-like entity that crawls over the substrate using coordinated movement. The slug can sense light, moisture, and other environmental cues and may migrate toward favorable conditions. The pseudoplasmodium is metabolically active and exhibits coordinated gene expression across cells, enabling differentiated development despite remaining a loosely organized collective.

Upon encountering suitable conditions, the slug undergoes culmination, in which the cells differentiate into a stalk and a fruiting body (sorus). The stalk elevates the spore-containing mass above the substrate, promoting dispersal. Spores produced in this stage are typically resistant and can germinate into new amoebae when conditions improve.

Terminology and scope: the term pseudoplasmodium is principally used for the migratory aggregation stage of cellular slime molds. It contrasts with plasmodial slime molds, whose plasmodium is a single multinucleate cytoplasmic mass. The pseudoplasmodium stage is reversible and can revert to solitary amoebae if conditions deteriorate or after spore dispersal.