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

Abstract

The cell wall of &lt;it&gt;Enteromorpha intestinalis&lt;/it&gt; (a marine alga) has been found to behave as a weakly cross-linked cation exchanger in NaCl solutions from 0.1–1020 mMolal (0.1–1000 mMolar). Anion adsorption could be described by Freundlich isotherms over this concentration range. The large anion, inulin carboxylate, was found to be a tracer of the anion free space of plant tissues only in salt solutions above 10 mMolal. The cell wall of &lt;it&gt;Enteromorpha&lt;/it&gt; has a cation exchange capacity of about 2500 μ mol g−1 dry wt. (Na&amp;plus; form). The cell wallvolume is a complex function of pH and the NaCl concentration. As a result, the cation exchange capacity is only predictable on a dry weight basis. The fixed negative charges of the cell wall have a p&lt;it&gt;K&lt;/it&gt;&lt;inf&gt;a&lt;/inf&gt; of2 &lt;it&gt;in situ&lt;/it&gt; and 1.75 &lt;it&gt;in vitro&lt;/it&gt;, and seem to be a mixture of sulphate and carboxyl sugar esters. The applicability of the Donnan equation to plant cell walls is discussed. Interpretation of the cell wall as a single thermodynamic phase is shown to be inappropriate. A large proportion of the cell wall solution is unaffected by the fixed anions.