Specific localization of a plant cell wall glycine-rich protein in protoxylem cells of the vascular system.

An antibody against glycine-rich protein 1.8 of bean (Phaseolus vulgaris L.) was used for immunogold/silver localization of the protein in different organs of the plant. In hypocotyls, ovaries, and seed coats, the protein was found specifically in xylem cells of the vascular tissue. In hypocotyls, only protoxylem cells were labeled with the antibody, which indicates a remarkable cell-type specificity for accumulation of this cell wall protein. In mature hypocotyls, the protein was restricted to the same subset of xylem cells but was no longer detected on tissue prints, where a positive antibody reaction depends on the transfer of soluble material from plant tissue to the nitrocellulose filter. This indicates that the glycine-rich protein is insolubilized in the cell wall during development. In longitudinal sections of tracheary elements of young hypocotyls and seed coats, the antibody stained a pattern very similar to that of the lignified secondary thickenings of the cell wall, which suggests a close functional relationship between glycine-rich protein and lignin deposition during cell wall biogenesis in protoxylem cells.