Thermotaxis by pseudoplasmodia of Dictyostelium discoideum.

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Abstract
The temperature dependence of migration rate and of the thermotactic sensitivity of pseudoplasmodia of D. discoideum was measured. Migration rate increases with temperature to 20.degree. C, is temperature insensitive from 20-27.5.degree. C, and decreases with temperature to 29.degree. C, above which point migration ceases. Pseudoplasmodia formed from cells grown at 23.5.degree. C are thermotactic only from 22-27.5.degree. C. Thus, a temperature dependence of migration rate is not sufficient to explain thermotaxis. Because random lateral movements by the pseudoplasmodia were not observed, the measurement of the temperature gradient appears to be spatial rather than temporal, with a half-maximal thermotactic response to a temperature gradient of about 0.04.degree. C/cm, or 0.0004.degree. C across an average pseudoplasmodium. Thermotactic sensitivity is adaptive, with pseudoplasmodia formed from cells grown at 20.degree. C capable of thermotaxis at temperatures lower than cells grown at 23.5.degree. C.