Removal by a Trace of Sodium of the Period Lengthening of the Potassium Uptake Rhythm Due to Lithium in Lemna gibba G3

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Abstract
The effect of Li+ on the period of the K+ uptake rhythm in the flow medium culture of the duckweed (Lemna gibba G3) was investigated under various ionic conditions. In the presence of Li+ at 0.2 millimolar or higher concentrations, the period was longer than the normal level of 25.4 hours by 2 hours. Li+ also lowered the amplitude of the rhythm. Although Na+ itself did not change any parameter of the rhythm, simultaneous application of Na+ at a very low concentration (20 micromolar) almost completely removed the effects of 0.5 millimolar Li+ on both the period and the amplitude. However, divalent cations (Ca2+ and Mg2+) or Rb+ did not remove the Li+ action on the period. The effect of Li+ and its removal by Na+ corresponded to intracellular Li+ and Na+ levels. The period was prolonged when the duckweed contained more Li+ than 5 micromoles/gram fresh weight. But the Li+ effect was cancelled when the in vivo Na+ level was greater than one-fifth that of Li+, even if the Li+ level exceeded over 5 micromoles/gram fresh weight.

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