PLANT PHYSIOLOGY , Vol 114, Issue 1 353-362, Copyright © 1997 by American Society of Plant Biologists
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DEVELOPMENT AND GROWTH REGULATION |
Phase Separation of Plant Cell Wall Polysaccharides and Its Implications for Cell Wall Assembly
A. J. MacDougall, N. M. Rigby and S. G. Ring
Department of Biochemistry, Institute of Food Research, Norwich Laboratory, Norwich Research Park, Colney, Norwich, NR4 7UA, United Kingdom
Concentrated binary mixtures of polymers in solution commonly exhibit
immiscibility, resolving into two separate phases each of which is enriched
in one polymer. The plant cell wall is a concentrated polymer assembly, and
phase separation of the constituent polymers could make an important
contribution to its structural organization and functional properties.
However, to our knowledge, there have been no published reports of the
phase behavior of cell wall polymers, and this phenomenon is not included
in current cell wall models. We fractionated cell walls purified from the
pericarp of unripe tomatoes (Lycopersicon esculentum) by extraction with
cyclohexane diamine tetraacetic acid (CDTA), Na2CO3, and KOH and examined
the behavior of concentrated mixtures. Several different combinations of
fractions exhibited phase separation. Analysis of coexisting phases
demonstrated the immiscibility of the esterified, relatively unbranched
pectic polysaccharide extracted by CDTA and a highly branched,
de-esterified pectic polysaccharide present in the 0.5 N KOH extract. Some
evidence for phase separation of the CDTA extract and hemicellulosic
polymers was also found. We believe that phase separation is likely to be a
factor in the assembly of pectic polysaccharides in the cell wall and
could, for example, provide the basis for explaining the formation of the
middle lamella.
