Deterination of Effective Partition Coefficients of Alkali Chlorides by Measurements of Concentration Potential across the Nitella flexilis (L.) Ag. Isolated Cell Wall

• Published in: Journal of Experimental Botany
• Main Authors: VOUÉ, MICHEL, GILLET, CLAUDE, DAHSE, INGO
• Format: Text
• Language: English
• Published: Oxford University Press 1990
• Subjects: Articles; Nitella flexilis
• Online Access: http://jxb.oxfordjournals.org/cgi/content/short/41/1/21; https://doi.org/10.1093/jxb/41.1.21

We report a study in which we estimate by means of non-equilibrium processes the value of an effective partition coefficient, x , a parameter that we use to take into account the non-ideal behaviour of the electrolyte of the external medium in the cell wall space. This parameter is defined by the ratio of the salt partition coefficient to the activity of the non-diffusing charges. To that purpose, concentration potential in NaCl, LiCI and CuCl 2 solutions was measured across an isolated cell wall of Nitella flexilis at different pH. No significant difference appeared between the potential values measured in the presence of NaCl or LiCl (pH 5.5, 4.0 and 3.0). At pH 3.0, in CuCl 2 solutions, the Nitella wall behaved as an uncharged membrane. Two methods—high concentrations and least-squares approximation-were used to calculate from these results the value of the effective partition coefficient. Both gave similar values of x At a given pH, the values of x are independent of the concentration of the external medium over a large range of concentration ratios. The activity of the exchange sites was estimated by the experimentally determined fraction of absorbed monovalent cations. The ionic concentrations in the wall space were calculated at pH 5.5 and 3.0 by introducing the values of x in the relations which correlate them to the ionic concentrations in the wall for that given value of the activity of the carboxylate sites. From their values, it appears that the negative fixed charges of the wall were functionally shaded by the condensation of a part of the adsorbed monovalent cations. The activity of the former was, therefore, reduced to a value considerably lower than that estimated by the cationic exchange capacity during equilibrium processes.