Compatible and incompatible rhizobia alter membrane potentials of soybean root cells.

Inoculation with Rhizobium japonicum or R. meliloti reduced the electrical transmembrane potential (E(m)) of soybean (Glycine max [L.] Merr.) root cells within 1 day. The response could be attributed to altered diffusion potential (E(D)). E(m) values return to control levels by the second day after inoculation, but again were reduced in R. meliloti-inoculated tissue on the seventh day. Increased concentrations of sodium phosphate in the perfusion solution magnified the effects of inoculation on E(m). Neither heat-killed rhizobia nor living cells of Pseudomonas fluorescens elicited the response. The E(m) and E(D) of nodule cells were nearly 20% lower than corresponding values from adjacent cortical cells of the root.