Blue light influences gene expression and motility in starving microplasmodia of Physarum polycephalum

The differentiation of starving Physarum polycephalum microplasmodia into resting structures (spherules) was studied. Early events in this differentiation pathway include decreases in both plasmodial motility and protein synthesis. The starving plasmodia show a blue light avoidance response. Blue light (lambda max 450 nm, irradiance 16 W/m2) acts antagonistically to the starvation stimulus so that spherule formation is inhibited [16]. Light affects each of the above mentioned events of the differentiation pathway: the migration rate of illuminated plasmodia is stimulated, the light avoidance response is irreversibly lost. The rate of incorporation of radioactive leucine into plasmodial protein remains at a higher level in illuminated plasmodia as compared to the decreasing rate during spherule formation in the dark. Protein degradation, uptake of external leucine, and the size of the internal leucine pool are not affected by light. Analysis by SDS-polyacrylamide gel electrophoresis of pulse-labelled plasmodial proteins reveals that blue light inhibits the synthesis of distinct starvation-induced proteins and allows continued synthesis of all major plasmodial proteins. Some of the blue light responses described are mimicked by alpha-amanitin suggesting that light might influence gene expression at the level of transcription.