Potassium Transport in Enteromorpha intestinalis (L.) Link: II. EFFECTS OF MEDIUM COMPOSITION AND METABOLIC INHIBITORS

In springwater (25.5 mol m^–3 Cl^–, 20.4 mol m^–3Na⁺, 0.14 mol m^–3 K⁺) Enteromorpha intestinalis couldnot survive for more than a few weeks unless provided with 0.5mol m^–3 K⁺ in the medium or alternatively exposed to seawaterfor 1 day per week. Maintenance of a cytoplasmic K⁺ level ofabout 200 mol m^–3 is critical for the maintenance of normalmetabolic activity. Net gains of intracellular K⁺ occurred whenthe plants were transferred from low-salinity to seawater; converselylarge net losses occurred when plants were transferred fromseawater to springwater. These two processes were not simplythe reverse of one another; net gain of K⁺ involved a largeincrease in the tracer flux both into and out of the cell butnet loss of K⁺ virtually halted the tracer flux into the cell.Any injury incurred by rapid salinity changes was short-lived;plants were rapidly able to adjust intracellular [K₁.K⁺). K⁺(orto some extent Rb⁺) was found to be necessary in the effluxmedium for ⁴²K⁺ exchange to occur. The osmotic concentrationof the medium was also important but extracellular Na⁺ and Cl^–concentrationswere not critical. K⁺ influx and efflux in both springwaterand seawater were largely independent of light and were sensitivein varying degrees to a range of common metabolic inhibitorsand uncouplers. The results are best explained by the presenceof an active K⁺ influx, generated by an ATP-dependent K⁺ pumpat the plasmalemma. Key words: Enteromorpha, Potassium transport, Salinity changes, Uncouplers, Inhibitors