Ion channels of intact young root hairs from Medicago sativa

Root hairs are a primary site for nutrient absorption and for initiation of signalling processes linked to variations of the root environment:plant-microbe interactions or abiotic changes. In many of these cases, the earliest detectable response is the modification of plasma membrane transports, detected through alteration of the electrical membrane potential. In spite of this, root hairs have not been extensively used in electrophysiological research so far. Problems with cell shape and current coupling are often prohibitive for microelectrode voltage-clamp on intact root hairs. In the present study, these difficulties have been overcome and the ion channel currents are described for young root hairs from alfalfa seedlings (Medicago sativa cv Sitel). Electrophysiological and pharmacological studies indicated an inward rectifying K+ time-dependent current. This current was sensitive to tetraethylammonium and Cs+ (10 mM each). Two other currents never shown in root hairs were described: an outward rectifying time-dependent K+ current, inhibited by tetraethylammonium and Cs+ (10 mM each) allowing K+ efflux under strong depolarizations and an instantaneous inward current identified as an anion current, inhibited by 4-acetamido-4ʹ-isothiocyanatostilbene-2,2ʹ-disulfonic acid and anthracene-9-carboxylic acid (100 μM each). These results should contribute to the understanding of root hair development and of signalling processes in M. sativa root hairs.