Pectin distribution at the surface of potato parenchyma cells in relation to cell-cell adhesion

The crispness of fruits and vegetables is dependent, predominantly, on the maintenance of cell adhesion. There is a growing body of evidence to suggest that cell adhesion in plants is controlled at the edge of cell faces rather than across the entire cell surface. The aim of the current study has been to exploit antibody-labeling techniques in conjunction with methods that induce cell separation to explore the distribution of highly esterified and weakly esterified pectic polysaccharides on the cell surface. Potato parenchyma tissue was subjected to cooking and chemical treatments, which induced softening through cell separation. Scanning electron microscopy (SEM) revealed characteristic patterns on the surface of these separated cells, which outlined the imprint of neighboring cells. Monoclonal antibodies, JIM5 and JIM7, were used to locate weakly esterified and highly esterified pectin by silver-enhanced immunogold SEM. The edge-of-face structures labeled strongly with JIM5 but not JIM7, indicating that they contained polygalacturonic acid of low ester content. In addition, adhesion of the middle lamella to the face of the primary wall was found to differ from adhesion at the edge of each cell face. This, in conjunction with the antibody-labeling observations, complements previous transmission electron microscopy studies and is consistent with the edge-of-face regions having a specialist role in cell adhesion.