Changes in pectin structure during epidermal cell elongation in pea (Pisum sativum) and its implications for cell wall architecture

Changes in cell wall architecture during elongation of epidermal cells in pea epicotyls were visualized by rapid-freezing and deep-etching (RFDE) techniques. The abundant network structure composed of the association of granular substances disappeared from the cell wall during elongation. The granular substances were demonstrated to be pectic polysaccharides by their disappearance upon EDTA treatment and by chemical analysis of the EDTA-extractable substances. Labeling with the monoclonal antibody JIM5, which recognizes unesterified pectins, was much more extensive in the cell walls of the non-elongating region than in those of the elongating region. The pore size of the cell wall was larger in the non-elongating region than in the elongating region. These observations suggest that the formation of the pectic gel itself is not involved in the control of the wall porosity. We proposed that the association of the granular substances is involved in the swelling of the cell walls in the elongating region.