A morphogen for the sporulation of Physarum polycephalum detected by cell fusion experiments.

The light stimulus, which under conditions of starvation induces the development of sporangia in the slime mold Physarum polycephalum, can be transferred from the light-exposed part to the unexposed part of a plasmodium by means of plasma circulation. A small quantity of protoplasm from a sporulating donor plasmodium, which had passed through the premorphogenetic phase, was transferred by a short period fusion with a briefly starved, light-induction-incompetent acceptor plasmodium. This led to sporulation and even to a reduction of the premorphogenetic phase from 9 down to 3 h in the acceptor plasmodium. After fusion with a sporulating plasmodium, a highly starved plasmodium from a non-sporogenic culture line or a growing plasmodium from a normal line prevents further morphogenesis of sporangia in the sporulating partner.