NaCl-stimulated proton efflux and cell expansion in sugar-beet leaf discs

The expansion of illuminated sugar-beet leaf discs floating on aqueous solutions is stimulated by 10 mM NaCl. During expansion, protons are pumped out of the cell and NaCl increases this proton flux by about 40%. The nett flux of K(+) and Na(+) into the discs was also evaluated. During the expansion period K(+) decreases while Na(+) increases markedly. The results indicate the existence of a sodium-stimulated proton pump which is active during cell enlargement.