A lipochito-oligosaccharide, Nod factor, induces transient calcium influx in soybean suspension-cultured cells

Lipochito-oligosaccharides (Nod factors) produced by Rhizobium or Bradyrhiz obium are the key signal molecules for eliciting nodulation in their corres ponding host legumes. To elucidate the signal transduction events mediated by Nod factors, we investigated the effects of Nod factors on the cytosolic [Ca2+] of protoplasts prepared from roots and suspension-cultured cells of soybean (Glycine max and G. soja) using a fluorescent Ca2+ indicator, Fura -PE3. NodBj-V (C18:1, MeFuc), which is a major component of Nod factors pro duced by Bradyrhizobium japonicum, induces transient elevation of cytosolic [Ca2+] in the cells of soybean within a few minutes. This effect is specif ic to soybean cells and was not observed in the tobacco BY-2 cells. Further more, NodBj-V without MeFuc did not induce any cytosolic [Ca2+] elevation i n soybean cells. Exclusion of Ca2+ from the medium, as well as pre-treatmen t of the cells with an external Ca2+ chelator or with a plasma membrane vol tage-dependent Ca2+ channel inhibitor, suppressed the Nod factor-dependent cytosolic [Ca2+] elevation. These results indicate that transient Ca2+ infl ux from extracellular fluid is one of the earliest responses of soybean cel ls to NodBj-V (C18:1, MeFuc) in a host specific manner.