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

In root-hair cells of Sinapis alba, cytosolic pH, cytosolic [Cl-], mem brane potential, and membrane resistance have been measured to investi gate proton-driven Cl- transport across the plasma membrane. Rapid low ering of the external pH transiently increased cytosolic [Cl-] and aci dified the cytoplasm. To an abrupt increase in external [Cl-] the cell s 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 wi th n > 1. Simultaneous recording of the membrane potential, the proton motive force, cytosolic pH, and cytosolic [CI-] reveals that kinetica lly this Cl- transport depends on the pH gradient across the plasma me mbrane rather than on the membrane potential.