Somatic incompatibility following plasmodial fusion between strains of the myxomycete Physarum polycephalum: the effect on their nuclei.

Fusion of plasmodia of strains 15 and 29 of the myxomycete Physarum polycephalum under appropriate conditions results in a lethal reaction visible to the naked eye. Examination by autoradiography and electron microscopy of areas in which the reaction is occurring shows that most of the nuclei derived from strain 29 (the sensitive strain) are enclosed in vesicles and are disintegrating, but that almost all those originating from strain 15 (the killer) are healthy. At this stage other organelles appear to be undamaged. These results support the view that the essential feature of the reaction is the elimination of the nuclei of the sensitive strain and that the ultimate destruction of large areas which occurs under a limited range of experimental conditions is a secondary effect which may not occur in nature.