Aj. Macdougall et al., PHASE-SEPARATION OF PLANT-CELL WALL POLYSACCHARIDES AND ITS IMPLICATIONS FOR CELL-WALL ASSEMBLY, Plant physiology, 114(1), 1997, pp. 353-362
Concentrated binary mixtures of polymers in solution commonly exhibit
immiscibility, resolving into two separate phases each of which is enr
iched in one polymer. The plant cell wall is a concentrated polymer as
sembly, 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 rep
orts of the phase behavior of cell wall polymers, and this phenomenon
is not included in current cell wall models. We fractionated cell wall
s purified from the pericarp of unripe tomatoes (Lycopersicon esculent
um) by extraction with cyclohexane diamine tetraacetic acid (CDTA), Na
2CO3, and KOH and examined the behavior of concentrated mixtures. Seve
ral different combinations of fractions exhibited phase separation. An
alysis of coexisting phases demonstrated the immiscibility of the este
rified, 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 ph
ase separation is likely to be a factor in the assembly of pectic poly
saccharides in the cell wall and could, for example, provide the basis
for explaining the formation of the middle lamella.