LIGHT‐INDUCED ACCUMULATIONS OF DICTYOSTELIUM DISCOIDEUM AMOEBAE

Abstract

Abstract— Light‐induced accumulations of amoebae of Dictyostelium discoideum in ‘light traps’ have been observed. The greatest accumulations are obtained with cell densities of about 8 × 10⁴ cells/mm². Accumulations are observed at incident fluence rates over about one decade both for white and for monochromatic light; higher fluence rates cause dispersal from the ‘light trap’. An action spectrum for the photoaccumulation, calculated from fluence‐response curves using the zero thresholds, shows a major peak between 405 and 410 nm and extends through most of the visible spectrum. This action spectrum does not coincide with any of the pigments known to be present in D. discoideum. The cellular basis for the photoaccumulation has been studied. No light effects on cell divisions or cell aggregation are observed during the 2 h duration of an accumulation experiment. Microvideographic analysis of single amoebae is consistent with the hypothesis that the amoebae are positively phototactic and move toward the light scattered from cells in the ‘light trap’, thus accumulating in the trap.