CHANGES IN DISTRIBUTION OF SHORT PECTIC POLYSACCHARIDES INDUCED BY MONOVALENT IONS IN THE NITELLA CELL-WALL

Nitella cell walls exhibit a major loss of pectin when the adsorbed bi valent ions are exchanged for monovalents. 2F4 monoclonal antibody, wh ich recognizes a conformational epitope of homogalacturonic acid induc ed by calcium ions, was complexed to colloidal gold and used to locali ze, by means of the electron microscope, the wall regions from which t he leakage occurred. Comparison of the labelling between nonpretreated cell walls and NaCl or LiCl pretreated ones, with or without incubati on in CDTA or in NaOH, reveals that monovalent ions induce the solubil ization of a pectic fraction rich in nonesterified galacturonic acids from the primary wall. Our results also indicate that in the secondary wall of Nitella, the pectic polysaccharides could be closely joined b y covalent crosslinking.