Thermotaxis of Dictyostelium discoideum amoebae and its possible role in pseudoplasmodial thermotaxis.

Thermotaxis by individual amoebae of Dictyostelium discoideum on a temperature gradient is described. These amoebae show positive thermotaxis at temperatures between 14 degrees C and 28 degrees C shortly (3 hr) after food depletion. Increasing time on the gradient reduces the positive thermotactic response at the lower temperature gradients (midpoint temperatures of 14, 16, and 18 degrees C), and amoebae show an apparent negative thermotactic response after 12 hr on the gradient. The thermotaxis response curve for "wild-type" amoebae after 16 hr on the gradient is similar to that shown for the pseudoplasmodia. Growth of the amoebae at a different temperature causes a shift in the thermotaxis response curve for the amoebae. This adaptation is similar to that shown for the pseudoplasmodia. Two mutants in thermotaxis, HO428 and HO813, show changes in amoebal thermotaxis similar to the observed changes in pseudoplasmodial thermotaxis. On the basis of the similarities between these responses, thermotaxis by the amoebae is proposed to be the basis for thermotaxis by the multicellular pseudoplasmodium.