Extra- and intracellular pH and membrane potential changes induced by K super(+), Cl super(-), H sub(2)PO sub(4) super(-), and NO sub(3) super(-) uptake and fusicoccin in root hairs of Limnobium stoloniferum

Short-term ion uptake into roots of Limnobium stoloniferum was followed extracellularly with ion selective macroelectrodes. Cytosolic or vacuolar pH, together with the electrical membrane potential, was recorded with microelectrodes both located in the same young root hair. The extracellular medium alkalinized when anion uptake exceeded K super(+) uptake. During fusicoccin-dependent plasmalemma hyperpolarization, extracellular and cytosolic pH remained rather constant. The extra- and intracellular pH changes, together with membrane depolarization, exclude mechanisms as K super(+)/A super(-) symport or HCO sub(3) super(-)/A super(-) antiport for anion uptake. Though not suitable to reveal the actual H super(+)/A super(-) stoichiometry, the results are consistent with an H super(+)/A super(-) cotransport mechanism.