Post-fusion Incompatibility in Plasmodia of Physarum Polycephalum

In the myxomycete Physarum polycephalum the somatic incompatibility between plasmodia of a killer strain and a sensitive strain is expressed as a lethal reaction (LR) in the sensitive strain within 6 h after fusion of both plasmodia. The lethal reaction was not caused by any of the extra-cellular compounds produced by the myxomycete nor was the result of intra-cellular compounds of the killer strain which were able to diffuse or could be transported into the Plasmodium of the sensitive strain. The lethal reaction could be prevented using inhibitors of RNA or protein synthesis applied within a certain time after fusion. This suggests that the sequence of events leading to the LR involves RNA and protein synthesis. These results are in agreement with genetic experiments which prove that the post-fusion incompatibility reaction is controlled genetically.