Cell‐wall separation during the outgrowth of lateral roots in Allium porrum L.

SUMMARY Cell‐wall modifications in the root tissues surrounding the lateral emerging roots of leek were investigated using morphological and in situ techniques. Primordium meristem cell walls were thin with a weak gold labelling after treatments for pectin and cellulose localization, as already described in other plant meristems. By contrast, the surrounding tissues of the mother roots displayed deep changes: their walls were swollen, thickened, with large intercellular spaces. Specific probes revealed a distribution of cellulose molecules comparable to the undisturbed root and a substantial increase in pectic material. Cell‐wall remnants were at the interface between the emerging roots and the mother root. They were rich in pectic material, but not in cellulose. Other immunogold experiments located a polygalacturonase over the primordium cells and its interface with the mother root. It is suggested that lateral root morphogenesis involves controlled cell separation, thanks to a specific interaction between pectinolytic enzymes and pectins.