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First published online August 4, 2006; 10.1104/pp.106.085712 Plant Physiology 142:696-709 (2006) © 2006 American Society of Plant Biologists Galactoglucomannans Increase Cell Population Density and Alter the Protoxylem/Metaxylem Tracheary Element Ratio in Xylogenic Cultures of Zinnia1 ová-Káko ovákováUnité Mixte de Recherche, Centre National de la Recherche Scientifique, Université Paul Sabatier 5546, Pôle de Biotechnologie Végétale, 31326 Castanet-Tolosan, France (A.B.-K., C.D., P.R., A.J., E.P., O.B., D.G.); Institute of Chemistry, Slovak Academy of Sciences, 845 38 Bratislava, Slovakia (A.B.-K., P.C., D.L.); and Department of Biochemistry, Downing Site, University of Cambridge, Cambridge CB2 1QW, United Kingdom (F.G., Z.Z., P.D.)
Xylogenic cultures of zinnia (Zinnia elegans) provide a unique opportunity to study signaling pathways of tracheary element (TE) differentiation. In vitro TEs differentiate into either protoxylem (PX)-like TEs characterized by annular/helical secondary wall thickening or metaxylem (MX)-like TEs with reticulate/scalariform/pitted thickening. The factors that determine these different cell fates are largely unknown. We show here that supplementing zinnia cultures with exogenous galactoglucomannan oligosaccharides (GGMOs) derived from spruce (Picea abies) xylem had two major effects: an increase in cell population density and a decrease in the ratio of PX to MX TEs. In an attempt to link these two effects, the consequence of the plane of cell division on PX-MX differentiation was assessed. Although GGMOs did not affect the plane of cell division per se, they significantly increased the proportion of longitudinally divided cells differentiating into MX. To test the biological significance of these findings, we have determined the presence of mannan-containing oligosaccharides in zinnia cultures in vitro. Immunoblot assays indicated that
1 This work was supported in part by the European Community (Marie Curie fellowship no. QLK3–CT–2001–60067to A.B.-K.) and the Slovakia Agency for the Support of Science and Technology (grant no. 51–013304), and by grants from the Biotechnology and Biological Sciences Research Council for work performed at Cambridge University. Preparation of galactoglucomannans was supported by the Slovak Grant Agency for Science (grant no. 2/4145/04). The author responsible for distribution of materials integral to the findings presented in this article in accordance with the policy described in the Instruction for Authors (www.plantphysiol.org) is: Deborah Goffner (goffner{at}scsv.ups-tlse.fr). www.plantphysiol.org/cgi/doi/10.1104/pp.106.085712 * Corresponding author; e-mail goffner{at}scsv.ups-tlse.fr; fax 33–5–62–19–35–02. Received June 23, 2006; accepted July 29, 2006; published August 4, 2006. This article has been cited by other articles:
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-1,4-mannosyl epitopes accumulate specifically in TE-inductive media. These epitopes were homogeneously distributed within the thickened secondary walls of TEs when the primary cell wall was weakly labeled. Using polysaccharide analysis carbohydrate gel electrophoresis, glucomannans were specifically detected in cell walls of differentiating zinnia cultures. Finally, zinnia macroarrays probed with cDNAs from cells cultured in the presence or absence of GGMOs indicated that significantly more genes were down-regulated rather than up-regulated by GGMOs. This study constitutes a major step in the elucidation of signaling mechanisms of PX- and MX-specific genetic programs in zinnia. 
