Blue light inhibits slime mold differentiation at the mRNA level

The influence of blue light on protein synthesis in spherulating Physarum polycephalum microplasmodia was studied using two-dimensional protein separation techniques. The starvation-induced plasmodium-spherule transition proceeds in the dark and is accompanied by the synthesis of 20 major differentiation-specific proteins as revealed by in vivo labelling with [35S]methionine. Three of these proteins are identical with cell wall components with respect to their mol. wts. (35 K, 34 K and 14 K) and isoelectric points. Spherulation is also accompanied by the appearance of 26 prominent differentiation-specific mRNA species translatable in the rabbit reticulocyte cell-free system. Six of the proteins synthesized in vitro co-migrate on two-dimensional gels with proteins labelled in vivo, two of them being cell wall components. Blue light, which inhibits spherulation completely, inhibits also the synthesis of spherule proteins and of spherule-specific mRNA activity. Only three protein components are induced by blue light, indicating that illumination does not induce a novel differentiated plasmodial state.