Theodorus W. J.
1Laboratory for Molecular Biology, MicroSpectroscopy Center Wageningen, Department of Plant Sciences, Wageningen University, Dreijenlaan 3, 6703 HA, Wageningen, The Netherlands; 2Signaux et Messages Cellulaires chez les Végétaux, UMR CNRS-UPS 5546, Pôle de Biotechnologie Végétale, 24 chemin de Borde Rouge, BP 17 Auzeville, 31326 Castanet-Tolosan, France
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Accepted 19 June 2003.
Nod factors are signaling molecules secreted by Rhizobium bacteria. These lipo-chitooligosaccharides (LCOs) are required for symbiosis with legumes and can elicit specific responses at subnanomolar concentrations on a compatible host. How plants perceive LCOs is unclear. In this study, using fluorescent Nod factor analogs, we investigated whether sulfated and nonsulfated Nod factors were bound and perceived differently by Medicago truncatula and Vicia sativa root hairs. The bioactivity of three novel sulfated fluorescent LCOs was tested in a root hair deformation assay on M. truncatula, showing bioactivity down to 0.1 to 1 nM. Fluorescence microscopy of plasmolyzed M. truncatula root hairs shows that sulfated fluorescent Nod factors accumulate in the cell wall of root hairs, whereas they are absent from the plasma membrane when applied at 10 nM. When the fluorescent Nod factor distribution in medium surrounding a root was studied, a sharp decrease in fluorescence close to the root hairs was observed, visualizing the remarkable capacity of root hairs to absorb Nod factors from the medium. Fluorescence correlation microscopy was used to study in detail the mobilities of sulfated and nonsulfated fluorescent Nod factors which are biologically active on M. truncatula and V. sativa, respectively. Remarkably, no difference between sulfated and nonsulfated Nod factors was observed: both hardly diffuse and strongly accumulate in root hair cell walls of both M. truncatula and V. sativa. The implications for the mode of Nod factor perception are discussed.
© 2003 The American Phytopathological Society