Ion channels of intact young root hairs from Medicago sativa François Bouteau a *, Anne-Marie Pennarun a , Armen Kurkdjian b , Monique Convert a , Daniel Cornel a , Michèle Monestiez a , Jean-Pierre Rona a , Ulrike Bousquet a a Electrophysiologie des membranes (LPCMSP), université Paris-7, CASE 7069, 2, place Jussieu, 75251 Paris cedex 05, France b Institut des sciences végétales, Centre national de la recherche scientifique, Bât. 22, avenue de la Terrasse, 91198 Gif-Sur- Yvette cedex, France (Received July 15, 1999; accepted October 22, 1999) Abstract — 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-4’- isothiocyanatostilbene-2,2’-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. © 1999 Éditions scientifiques et médicales Elsevier SAS Ion channels / root hairs / alfalfa / single-electrode voltage-clamp A9C, anthracene-9-carboxylic acid / dSEVC, discontinuous single-electrode voltage-clamp technique / E act , activation potential / E m , resting membrane potential / E rev , reversal membrane potential / IIAC, instantaneous inward anion current / IRKC, inward rectifying K + current / I-V, current-voltage relationships / NA, niflumic acid / IAA-94, R(+)-methylindazone; indanyloxyacetic acid 94 / NPPB, 5-nitro-2-(3-phenylpropyl amino)-benzoic acid / ORKC, outward rectifying K + current / SBS, standard buffer solution / SITS, 4-acetamido-4’-isothiocyanatostilbene-2,2’- disulfonic acid / TEA, tetraethylammonium chloride / TPA, tetrapenthylammonium chloride / V h , holding membrane potential 1. INTRODUCTION Root hairs are differentiated epidermal cells which, by increasing the absorbing surface of the root, play a major role in the uptake of nutrients and water [32]. Root hairs also behave like sensors able to perceive signals from their environment [32]. Changes in plasma membrane transports represent an early response of plant cells to various signals, such as hormones [8, 17], elicitors [31, 41], toxins of bacterial origin ([25] and references therein), wounding signals such as systemin [29, 30], light and other environmen- tal signals [22]. The response to these signals is mediated by ion fluxes (mainly H + , Cl – , Ca 2+ and K + ), which are activated or inhibited (see [47] for reviews). Several reports have described anion currents [34, 48] and cation currents [9, 23, 48] in various root cells but only a few reports describe ion channel currents specific to root hairs. Gassmann and Schroeder [13] reported the presence of a K + inward rectifying current activated at hyperpolarized membrane voltages in wheat root hair protoplasts, using the patch-clamp technique. Lew [19] also recorded inward K + currents (elicited within 50 ms) in Arabidopsis thaliana intact root hairs using the double-barrelled microelectrode voltage-clamp technique. * Author to whom correspondence should be addressed (fax +33 1 44 27 78 13; e-mail bouteau@ccr.jussieu.fr) Plant Physiol. Biochem., 1999, 37 (12), 889-898 / © 1999 Éditions scientifiques et médicales Elsevier SAS. All rights reserved S0981942899001011/FLA Plant Physiol. Biochem., 0981-9428/99/12/© 1999 E ´ ditions scientifiques et médicales Elsevier SAS. All rights reserved