Phase Shift in the Potassium Uptake Rhythm of the Duckweed Lemna gibba G3 Caused by an Azide Pulse.

A 6-hour application (6-hour pulse) of 1 millimolar azide significantly changed the phase of the potassium uptake rhythm of Lemna gibba G3. The phase response curve obtained was type 0 and very similar to that caused by a 6-hour pulse of low temperature (5 degrees C) or darkness. The magnitude of the phase shift and the type of the phase response curve depended on the concentration of azide. However, 6-hour pulses of 3 millimolar cyanide or 10 micromolar (3-(3,4-dichlorophenyl)-1,1-dimethylurea) failed to shift the phase of the rhythm, while these pulses lowered the rate of carbon dioxide uptake or release. Azide, even at 3 micromolar, selectively reduced the amplitude of the rhythm without inhibiting the mean level of potassium uptake.