AN ACTION SPECTRUM FOR PHOTOTAXIS BY PSEUDOPLASMODIA OF Dictyostelium discoideum

The sensitivity of phototactic orientation of pseudoplasmodia (slugs) of the cellular slime mold Dictyosrelium discoideum has been measured for white light and monochromatic light using computer aided directional statistics. The zero threshold for white light was found at about 10‐5 Ix. An action spectrum for positive phototaxis has been calculated from fluence rate‐response curves; it shows two major maxima at about 420 and 440 nm and secondary peaks at 560 and 610 nm. This action spectrum is significantly different from the one for phototactic orientation in Dictyostelium amoebae.