Lipochito-oligosaccharides, Nod factors secreted by Rhizobium bacteria, are signal molecules that induce deformation of root hairs of their host plant. A bioassay was used for deformation, and the cytological changes induced by specific lipochito-oligosaccharides in root hairs of Vicia sativa L. (vetch), grown between glass slides, were examined. In the assay, root hairs of a particular developmental stage, those that were terminating growth, were susceptible to deformation. These hairs obtained characteristics of tip-growing cells again: (i) a polar cytoplasmic organization and reverse fountain streaming, (ii) an accumulation of a spectrin-like antigen at the tip, and (iii) a tip-focused calcium gradient. Calcium gradients were visualized in Indo-1 loaded root hairs with UV confocal microscopy and ratio-imaging. The results show that hairs respond to the bacterial signal by recovering cytoplasmic polarity and exocytosis.