Pectin onion

Fig 4 FTIR spectra of walls of DCB-adapted and non-adapted tomato suspension cells, onion parenchyma cell walls, and polygalacturonic acid (Sigma), a = ester peak, b = free acid stretches from pectins, y axis is absorbance, X axis is wavenumber (frequency inverse). 

The Fourier Trairsform Infrared (FTIR) spectrum obtained from non-adapted tomato cell walls is very similar to that from the onion parenchyma cell wall (both contain cellulose, xyloglucan and pectin) although there is more protein in the tomato walls (amide stretches at 1550 and 1650 cm-i) (Fig 4). In DCB-adapted tomato cell walls, the spectrum more closely resembles that of either purified pectins or of a commercial polygalacturonic acid sample from Sigma with peaks in common at 1140, 1095, 1070, 1015 and 950 cm-t in the carbohydrate region of the spectrum as well as the free acid stretches at 1600 and 1414 cm-i and an ester peak at 1725 cm-k An ester band at 1740 cm-i is evident in both onion parenchyma and non-adapted tomato cell wall samples. It is possible that this shift in the ester peak simply reflects the different local molecular environment of this bond, but it is also possible that a different ester is made in the DCB-adapted cell walls, as phenolic esters absorb around 1720 cm-i whilst carboxylic esters absorb at 1740 cm-k The... 

In some species, onion (2), tomato, and sugar beet (13), the interface regions between cells, ie the middle lamella and the cell corners, are rich in relatively unesterified pectins which may function in cell-cell adhesion and play an important structural role in tissue integrity. Cell corners, in particular, may act as joists in the scaffolding function of the wall, bearing much of the mechanical load of the tissue (Jeronomidis, pers. comm.). In Zinnia leaves, although all of the cell-walls contain methyl-esterified pectin. 

Our solid state NMR findings suggest that three distinct groups of pectins differing in mobility on the kHz frequency scale, coexist in at least two different areas of the onion cell wall. 

In addition to the highly mobile pectin described in section 2.1, two further mobility classes of pectic galacturonans could be seen within the onion cell wall (figure 3). 

It has been suggested that in cell walls other than those of onions, different types of pectic matrix are present in different parts of the wall (17). This work clearly demonstrates the existence of at least two spatially separate pectic matrices with polymers having at least two conformational forms and three distinct mobilities. It suggests pectins are more than just pore fillers within the plant cell wall. 

A FIGURE 6-33 Schematic representation of the cell wall of an onion. Cellulose and hemicellulose are arranged into at least three layers in a matrix of pectin polymers. The size of the polymers and their separations are drawn to scale. To simplify the diagram, most of the hemicellulose cross-links and other matrix constituents (e.g., extensin, lignin) are not shown. [Adapted from M. McCann and K. R. Roberts, 1991, in C. Lloyd, ed.. The Cytoskeletal Basis of Plant Growth and Form, Academic Press,... 

The recovery and degradation of sugars from potato pectin fractions by hydrolysis with 2M trifluoroacetic acid has indicated that between 61 and 96% of each sugar residue was recovered, depending on the monosaccharide residue. Lower recoveries were obtained from intact onion cell walls. 

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