Summary

Peroxidases were localized in differentiating xylem cells of Populus spp. by means of immunogold labelling in combination with transmission electron microscopy (TEM). Polyclonal antibodies raised in rabbits against horseradish peroxidase were used for these experiments. Within the cytoplasm, TEM revealed a distinct labelling of the dictyosomes, indicating that these organelles are involved in the transport of peroxidases to the plasma membrane. During the formation of primary and secondary walls, cell corner regions became distinctly labelled, the developing secondary wall layers to a much lesser degree. Significant differences in the immunogold labelling between the intercorner middle lamella and the secondary cell wall layers were not observed. According to the immunogold labelling, peroxidases are incorporated into the secondary wall more or less simultaneously with deposition of polysaccharides. Correlations between peroxidase incorporation and lignification are discussed.