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The pore size of non-graminaceous plant cell walls is rapidly decreased by borate ester cross-linking of the pectic polysaccharide rhamnogalacturonan II

Author:
Fleischer, A., O'Neil, M.A., Ehwald, R.
Source:
Plant physiology 1999 v.121 no.3 pp. 829-838
ISSN:
0032-0889
Subject:
pectins, cell walls, chelating agents, Chenopodium album, nutrient deficiencies, calcium, boron, cations, magnesium, pH, esters, sodium, polymers, borates, culture media, cell suspension culture, inorganic ions
Abstract:
The walls of suspension-cultured Chenopodium album L. cells grown continually for more than 1 year on B-deficient medium contained monomeric rhamnogalacturonan II (mRG-II) but not the borate ester cross-linked RG II dimer (dRG-II-B). The walls of these cells had an increased size limit for dextran permeation, which is a measure of wall pore size. Adding boric acid to growing B-deficient cells resulted in B binding to the wall, the formation of dRG-II-B from mRG-II, and a reduction in wall pore size within 10 min. The wall pore size of denatured B-grown cells was increased by treatment at pH < or = 2.0 or by treatment with Ca(2+)-chelating agents. The acid-mediated increase in wall pore size was prevented by boric acid alone at pH 2.0 and by boric acid together with Ca(2+), but not by Na(+) or Mg(2+) ions at pH 1.5. The Ca(2+)-chelator-mediated increase in pore size was partially reduced by boric acid. Our results suggest that B-mediated cross-linking of RG-II in the walls of living plant cells generates a pectin network with a decreased size exclusion limit for polymers. The formation, stability, and possible functions of a borate ester cross-linked pectic network in the primary walls of nongraminaceous plant cells are discussed.
Agid:
666697