Freeze-dried surface replicas of tobacco pectin gels and noncutinized lower epidermal cell surfaces compared

Abstract

Pectic polysaccharides play an important role in the extracellular matrix of land plant tissues. Pectins are found in primary cell walls and in the connecting region between cells, the middle lamella. These polysaccharides are thought to function as a binding material within cell walls and between cells. Pectins contain galacturonosyl residues as a major constituent and varying amounts of neutral sugar residues. A portion of the galacturonosyl residues are methyl-esterlfted. Calcium salts of pectin are thought to be present in primary cell walls and middle lamella. The structure of the calcium bond between interfiber galacturonosyl residues has been suggested by x-ray fiber diffraction work. The pectic acid unit cell indicates that the galacturonosyl residue as viewed down the chain axis is roughly 7.2 x 6.8Å along the two crystallographlc a and b axes. One or two waters of hydration can Increase this size by 3-6Å In freeze-etched preparations or an associated calcium Ion can Increase Its cross-sectional dimensions by about 2Å.