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

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 (Ca(2+) and Mg(2+)) 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.