Ion currents involved in early Nod factor response in Medicago sativa roothairs: a discontinuous single-electrode voltage-clamp study

Nod factor [NodRm-IV(Ac,S)], isolated from the bacterium Rhizobium meliloti , induces a well-known depolarization in Medicago sativa (cv Sitel) root ha irs. Analysis of this membrane response using the discontinuous single-elec trode voltage-clamp technique (dSEVC) shows that anion channel, K+ channel and H+-ATPase pump currents are involved in young growing root hairs. The e arly Nod-factor-induced depolarization is due to increase of the inward ion current and inhibition of the H+ pump. It involved an instantaneous inward anion current (IIAC) and/or a time-dependent inward K+ current (IRKC). The se two ion currents are then down-regulated while the H+ pump is stimulated , allowing long-term rectification of the membrane potential (E-m). Our res ults support the idea that the regulation of inward current plays a primary role in the Nod-factor-induced electrical response, the nature of the ions carried by these currents depending on the activated anion and/or K+ chann els at the plasma membrane.