XVI International Botanical Congess

An antibody against a plant arabinogalactan associated with AGP found in tobacco and other plants labels a reticulum on the surface of BY-2 protoplasts. Antibodies against another plant protein, wall associated kinase=WAK, label vertices of the reticulum. WAK is known to bind to the wall, cross the membrane, and extend into the cytoplasm. Diverse other proteins are demonstrated at the vertices by well-controlled labeling of epitopes recognized by antibodies against animal interim, vitronectin, and two fibronectins. In depectinated wall, antibodies against WAK, vitronectin, and fibronectin recognize a distribution of puncta similar to the distribution of vertices in the reticulum. These and other evidences suggest functions of the reticulum: 1) its vertices are sites of adhesion, 2) it is a mechanical force-bearing and force-focusing structure associated with the membrane, 3) it defines positions of attachment for the cortical ER. Its existence suggests constraints on mechanisms proposed for cell expansion and differentiation.