Capacity of enucleated amoebae to recognize and respond to heterologous cytoplasm.

When amoebae are injected with heterologous cytoplasm from another type of amoeba, cellular organelles are segregated and degenerate within membrane-bounded spaces in the host's cytoplasm. In the present study, the role of the nucleus in this response was tested by injecting heterologous cytoplasm from Pelomyxa carolinensis into enucleate and enucleate Amoeba discoides. Samples were prepared for ultrastructural study at intervals between 15 min and 2d after the operation. In enucleate recipients of heterologous cytoplasm, organelles and cellular debris were observed in vacuole-like spaces indistinguishable in morphology and frequency from those of nucleated recipients. When donor cytoplasm included thoria particles, the electron-dense tracer was found along with degenerating organelles in the vacuole-like structures, confirming the presence there of injected cytoplasm. changes of comparable magnitude were not observed when either nucleated or enucleated cells were injected with homologous cytoplasm. The results indicate that nuclear activity is not necessary for the ultrastructurally observable responses of amoebae to heterologous cytoplasm. It is suggested therefore that the cytoplasm possesses a mechanism for recognition of at least some types of heterologous organelles.