Serine Transport and Membrane Depolarization in the Liverwort Riccia fluitans

Abstract
The plasmalemma of thallus cells of the aquatic liverwort, Riccia fluitans, is reversibly depolar­ized by ʟ- and ᴅ-serine. At 0.1 mᴍ K+ in the medium, the depolarization saturates at 50 mV; half-maximal depolarization occurs at 13 μᴍ ʟ-serine and 30 μᴍ ᴅ-serine, respectively. Uptake of 14C-­labelled ʟ-serine depends upon the K+ concentration and is sensitive to the membrane potential as indicated by its reduction through 1 mᴍ sodium cyanide. We propose that serine binds to and is transported by an electrogenic carrier. However, an interaction of serine with K+ channels of the membrane seems also possible.

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