Role of the Differentiation of Root Epidermal Cells in Nod Factor (from Rhizobium meliloti)-Induced Root-Hair Depolarization of Medicago sativa

The stage of differentiation of epidermal cells and the development of root hairs was found to be important for the induction of depolarization in root hairs of Medicago sativa by Nod factor [NodRm-IV(S)] isolated from the bacterium Rhizobium meliloti. The electrical membrane response was concentration dependent, having its major effect (amplitude of the depolarization and number of root hairs that responded) at 10-8 and 10-7 M Nod factor. This response was correlated with a morphological effect of Nod factor in the root-hair-deformation bioassay at similar concentrations. The effect of Nod factor on depolarization and root-hair deformation showed specificity with respect to the structure, since unsulfated Nod molecules were inactive, as was the synthetic N,N',N",N"'- tetraacetylchitotetraose. The Nod factor that is O-acetylated at the nonreducing sugar was as efficient in root-hair deformation and membrane depolarization as the sulfated Nod factor.