DisplayTitle

Cation Fluxes Cause Plasma Membrane Depolarization Involved in β-Glucan Elicitor-Signaling in Soybean Roots

¹Max-Planck-Institut für Chemische ökologie, Bioorganische Chemie, Hans-Knöll-Str. 8, D-07745 Jena, Germany; ²Department Biologie I der Ludwig-Maximilians-Universität, Botanik, Menzinger Str. 67, D-80638 München, Germany; ³Botanisches Institut I, Universität Gießen, Senckenbergstraße 17, D-35390 Gießen, Germany

Inducible and specific ion fluxes on plasma membranes represent very early events during elicitation of plant cells. The hierarchy of such ion fluxes involved is still unknown. The effect of Phytophthora sojae-derived β-glucan elicitors on the plasma membrane potential as well as on surface K⁺, Ca²⁺, and H⁺ fluxes has been investigated on soybean roots using ion-selective microelectrodes. β-Glucans with different degrees of polymerization transiently depolarized the plasma membrane. The elicitor concentration necessary for half-maximal depolarization closely resembled the corresponding binding affinities of soybean root membranes toward the respective β-glucans. Upon repeated elicitor treatment, the root cells responded partially refractory, suggesting a complex responsiveness of the system. Within the root hair space, characteristic decreasing K⁺- and Ca²⁺-free concentrations were induced by the elicitors, probably causing depolarization through the influx of positive charges. Whereas K⁺ fluxes were inverted after passing the K⁺ equilibrium (Nernst-) potential, Ca²⁺ influx continued. No anion fluxes sufficient to account for charge compensation were observed under the same experimental conditions. K⁺ and Ca²⁺ fluxes as well as depolarization were inhibited by 100 μM or less of the Ca²⁺ antagonist La³⁺. Contrasting other systems, in soybean the main cause for elicitor-induced plasma membrane depolarization is the activation of cation instead of anion fluxes.

Additional keywords: β-Glucan receptor, Glycine max.