23Na and 7Li NMR study of Nitella cell walls before and after an ion-induced loss of the cationic exchange capacity

23 Na- and 7 Li-NMR studies were conducted on isolated cell walls of Nitella to monitor the changes induced in the pectin matrix after the cation exchange capacity was reduced to about 60% of its initial value by a pretreatment with a 500 mM LiCl solution. Walls in Ca 2+ form were exchanged with NaCl and LiCl solutions before and after this pretreatment. In the whole cell wall equilibrated with 10, 35 and 100 mM NaCl solutions or mixtures at the same total concentrations of Na + and Li + in the same proportions, the 23 Na- and 7 Li-NMR spectra were all characterized by only one signal. The Na + and Li + relaxation times were drastically shorter than those recorded in aqueous solution but the two Na + relaxation rates increased linearly with the Na + concentration in the external solutions