Xyloglucans

Both types of xyloglucans exhibit monolayer sorption onto cellulose (116) and tamarind xyloglucan exhibits maximum specific sorption onto cellulose less than that of coniferous xylan. By inference with other data, this is also less than that of glucomannan and hardwood xylan, but similar to many additives used in the paper industry. 

Xyloglucans are classified as gum when they are extractable with hot water from seed endosperm cell walls, such as the tamarind seed xyloglucan, and as hemicelluloses because they are alkali-extractable from the cell walls of vegetative plant tissues where they are closely associated with cellulose [2]. Also /3-glucans with mixed linkages appear under the name gum as well as hemicellulose in the literature. 

Fig. 14 Effect of the molecular weight of tamarind seed xyloglucan depolymerized by ( ) 7-irradiation, ( ) ultrasonication, and ( ) endo-glucanase treatment on the production of various cytokines (Tumor necrosis factor a, TNE-a Interleukin 8, IL-8 Interleukin 10, IL-10 and Interleukin 12, IL-12) in HaCaT cells (Immortalized keratinocytes line) [301]...

From tamarind seed xyloglucan, carboxymethyl derivatives with different levels of DS were prepared in isopropanol medium [440]. Swelling power, solubihty and tolerance to organic solvents of the derivatives increased with increasing DS. The interaction properties of the unmodified xyloglucan with calcium chloride and sodiiun tetraborate were found to be reversed upon car-boxymethylation. 

This essay was written in an attempt to explain our overview of primary cell walls and to reach consensus on the nomenclature of primary cell wall polysaccharides. We present evidence supporting the hypothesis that cellulose, xyloglucan, arabinoxylan, homogalacturonan, RG-I, and RG-II are the six polysaccharides common to all primary cell walls of higher plants. In many cells, these six polysaccharides account for all or nearly all of the primary wall polysaccharides. Like the physically interacting proteins that constitute the electron transport machinery of mitochondria, the structures of the six patently ubiquitous polysaccharides of primary cell walls have been conserved during evolution. Indeed, we hypothesize that the common set of six structural polysaccharides of primary cell walls have been structurally... 

In the absence of suitable cell wall mutants, DCB-adapted tomato cells provide an opportunity to characterise the pectin network of the plant cell wall. It should be noted that synthesis and secretion of hemicellulose is not inhibited but, in the absence of a cellulose framework for it to stick to, most of the xyloglucan secreted remains in soluble form in the cells culture medium (9, 10) while other non-cellulosic polysaccharides and other uronic-acid-rich polymers predominate in the wall. 

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... 

If we compare liquefaction to maceration, more activities are needed to liquefy the cell wall. Since 1991, new pectinases activities such as rhamnogalacturonase, pectin acetylesterase and xyloglucanases complex have been found to be important in the apple liquefaction by Henck Schols, Jean-Paul Vincken and Voragen [3]. The cellulose-xyloglucan complex accounts approximatively 57% of the apple cell-wall matrix. In a liquefaction process, an efficient enzymic degradation of this complex is crucial to increase the sugars extraction, to decrease the viscosity of the pulp then to be able to ultra-filtrate the juice without second depectinisation, at last to have negative alcohol tests required by some concentrate customers. 

Both the 2, helix and the 3, helix are represented in the low mobility spectrum of polymers close to cellulose (figure 4), although there was some interference from xyloglucan signals. 

There are a number of possible locations within the cell wall for the pectin further away from cellulose. If there are covalent links between pectins and xyloglucans (16), then pectic chain segments close to these links would appear in the region sharing the same mean mobility characteristics as cellulose. The majority of the pectic molecule, diverging from the microfibrils would appear in the region with greater mean mobility. 

Hrmova, M., Farkas, V., Lahnstein, J., and Fincher, G.B. (2007) A barley xyloglucan xyloglucosyl transferase covalently links xyloglucan, cellulosic substrates, and (l,3 l,4)-D-glucans. J. Biol. Chem. 282, 12951-12962. 

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