Poster: Cell Walls

Abs # 1243: Xylem parenchyma cells deliver the H₂O₂ necessary for the polymerization of cinnamyl alcohols in the secondary cell wall of xylem vessels as another example of cell-to-cell cooperation during lignin biosynthesis

Presenter:	Ros Barceló, Alfonso R., rosbarce@um.es
Authors	Ros Barceló, Alfonso R. (A)   Pomar, Federico  (A)
Affiliations:	(A): University of Murcia

The temporal phase of lignification of the xylem in Zinnia elegans stems is characterized by a burst in H₂O₂ production, whose fate is to be used by xylem peroxidases for the polymerization of cinnamyl alcohols into lignins. This burst in H₂O₂ production is sensitive to inhibitors of the phagocytic NADPH oxidase of mammalian cells, and to inhibitors of the metabolic cascade of inositol-1,3,5-triphosphate in plant cells. Search for the sites of H₂O₂ production (NADPH oxidase localization) in the lignifying xylem of Z. elegans stems using simultaneously optical (polarized and epi-polarized fluorescence) and electron (CeCl₃) microscope techniques revealed that H₂O₂ production take place in the outer-face of the plasma membrane of particular xylem parenchyma cells, from where it diffuses to adjacent and differentiating xylem vessels. H₂O₂ diffusion occurs mainly through the continuous cell wall space, and both experimental data and theoretical calculations suggest that H₂O₂ diffusion itself from its sites of production does not limit peroxidase-mediated lignin construction. Preliminary search for NADPH oxidase sequences in data bases suggest that this putative Z. elegans NADPH oxidase forms a closed cluster within putative NADPH oxidases from dicotyledons, while putative NADPH oxidases from monocotyledons form a divergent linage within vascular plant evolution. This work was supported by the grants BOS2002-03550 (MCYT) and PI-70/00615/FS/01 (Fundación Séneca)