Participation of a membrane system in the potassium uptake rhythm in a duckweed, Lemna gibba G3

Abstract

The period of the free-running potassium uptake rhythm in a long-day duckweed, Lemna gibba G3, was lengthened by Li+ and shortened by ethanol. This suggests that a membrane system participates in the circadian feed-back system. High temperature treatment (39°C) increased the motion of the rhythm when applied during periods of high potassium uptake (CT 18–06), and decreased it when applied during low potassium uptake (CT 06–18), which indicates a circadian change in the properties of the membrane. However, modification of the potassium uptake level caused by temperature change, application of valinomycin, or a change in the ambient potassium concentration caused no modification in the phase of the rhythm. Thus, the oscillator involved probably is not located in the cell membrane or the ectoplasm.