THE H+/CL- SYMPORTER IN ROOT-HAIR CELLS OF SINAPIS-ALBA

In root-hair cells of Sinapis alba, cytosolic pH, cytosolic [Cl-], membrane potential, and membrane resistance have been measured to investigate proton-driven Cl- transport across the plasma membrane. Rapid lowering of the external pH transiently increased cytosolic [Cl-] and acidified the cytoplasm. To an abrupt increase in external [Cl-] the cells reacted with a rapid initial depolarization and a subsequent slower hyperpolarization, which was accompanied by an increase in cytosolic [Cl-] and [H+]. These results are indicative of an nH(+)/Cl- symport with n > 1. Simultaneous recording of the membrane potential, the proton motive force, cytosolic pH, and cytosolic [CI-] reveals that kinetically this Cl- transport depends on the pH gradient across the plasma membrane rather than on the membrane potential.