Ion Exchange Fluxes of the Cell Walls ofEnteromorpha intestinalis(L. ) Link (Ulvales, Chlorophyta)

The 22Na+ and 36CI− exchange properties of the cell walls of Enteromorpha intestinalis (L. ) Link in simple monovalent salt systems have been shown to be similar to a ‘leaky’ cation exchange membrane rather than a homogeneous membrane. The ion exchange properties of the cation and anion cell wall contents are what would be expected of a cation exchange membrane i. e. anion exchange is strongly dependent on the bathing electrolyte concentration and becomes very slow in dilute salt. This would lead to the cell wall becoming a barrier to anions in dilute salt. However, measurements of the anion flux across cell walls in living and dead tissues show that anion exchange across cell walls is facilitated by pores. The exchange kinetics of the bulk of the cell wall anions does not limit the anion flux across cell walls of this plant. It is concluded that the cell wall is not a critical limitation to plasmalemma fluxes of the living plant and that unstirred layers are more important than cell walls in the measurement of anion flux rates.