Cation Exchange Properties of the Cell Walls of Enteromorpha intestinalis (L.) Link. (Ulvales, Chlorophyta

The cell wall of Enteromorpha intestinalis (a marine alga) hasbeen found to behave as a weakly cross-linked cation exchangerin NaCl solutions from 0.1–1020 mMolal (0.1–1000mMolar). Anion adsorption could be described by Freundlich isothermsover this concentration range. The large anion, inulin carboxylate,was found to be a tracer of the anion free space of plant tissuesonly in salt solutions above 10 mMolal. The cell wall of Enteromorphahas a cation exchange capacity of about 2500 µ mol g^–1dry wt. (Na+ form). The cell wallvolume is a complex functionof p^H and the NaCl concentration. As a result, the cation exchangecapacity is only predictable on a dry weight basis. The fixednegative charges of the cell wall have a pK_a of2 in situ and1.75 in vitro, and seem to be a mixture of sulphate and carboxylsugar esters. The applicability of the Donnan equation to plant cell wallsis discussed. Interpretation of the cell wall as a single thermodynamicphase is shown to be inappropriate. A large proportion of thecell wall solution is unaffected by the fixed anions.