Diurnal change in leakage of electrolytes from a long-day duckweed,Lemna gibbaG3, under osmotic stress induced by water treatment

摘要

The leakage of electrolytes fromLemna gibbaG3 placed on water was investigated in terms of the change in the electroconductivity of the ambient water. Amounts of the leaked electrolytes reached a maximum 5–6 hr after transfer to water, followed by gradual decrease. The maximum amount of the leakage changed diurnally, with the time of the water treatment, with a peak in the early subjective day and a trough in the early subjective night. The rhythm was reset by a light-on signal, persisted for at least 3 days under continuous light, and its period was temperature-compensated. The rhythm was maintained even in the presence of 2,4-dinitrophenol or 3-(3,4-dichlorophenyl) 1,1- dimethylurea and under weak light, suggesting that a change in passive efflux of electrolytes was involved, and this was confirmed by kinetic studies which revealed that the leakage occurred by simple diffusion. Strong illumination extinguished the rhythm, probably by promoting the active reabsorption of the leaked ions. Potassium ions were the major cations found, to the leakage of which was attributed half of the change in the electroconductivity of the ambient wate