Barley cell-walls

Some monocot, primary cell-wall polysaccharides may be cross-linked by esters of ferulic acid (4-hydroxy-3-methoxycinnamic acid). There is evidence for the existence of such cross-links in monocot tissues containing secondary walls, including Italia ryegrass stem276 and wheat endosperm.277 Ferulic acid is also present in barley cell-wall,278 and it has been reported that treatment with base releases ferulic acid from the cell walls of several Graminae,276 supporting the idea that ferulic acid is bound to the wall as an ester. However, ferulic acid has not, so far, been reported to be present specifically in primary cell-walls in either monocots or dicots. 

Enzyme-Mediated Substrate Immunolocalization ofPoIygalacturonic Acid Within Barley Epidermal Cell Walls Utilizing Endopolygalacturonase of Cochliobolus sativus and a Monoclonal Antibody Specific for the Enzyme... 

Figure 1. Transverse section of barley leaf epidermal cells taken perpendicular to the long axis of the cells and anticlinal to the leaf surface. The section has been labeled by the EMSIL technique (see Methods) utilizing purified C. sativus endopolygalacturonase and monoclonal antibody EPG-4, which is specific for this enzyme, in order to localize the substrate of the enzyme at the typical site penetrated by the fungal pathogen. Bar = 1 pm. Inset Comparable cell wall region as in Fig. 1 but labeled with monoclonal antibody JIM 5 to localize non-esterified pectin. Bar = 1 pm. Note the identical labeling patterns obtained with either method.

Figure 2. Advanced stage of barley leaf penetration by C. sativus. The pathogen has penetrated the anticlinal cell wall junction between two host epidermal cells (e). The fungal appressorium (a) is visible above the cell comer. The host cell comer matrix has been displaced by an enlarged hyphal element (h) situated between the thin cell walls of the host epidermal cells. The host epidermal cell walls have been densely labeled with the cellulase-gold probe. An intercellullar hyphal element (ih) is present within the penetrated host cell. Bar = 1 pM.

Phenolic Acid or Aldehyde (mg g 1 cell walls) Maize Stem(6) Barley Stem(6) Wheat Bran(6) Italian Ryegrass Shoot(7)... 

At least some ferulic acid units in the cell walls of vegetative parts of sugar cane, maize and barley are esterified via the carboxyl group to arabinose units (12-14). This was established by treatment of these... 

Endosperm cell-walls of barley and oats Palm kernels, lupin seed... 

Linnestad, C., D. N. P. Doan, R. C. Brown, et al. Nucellain, a barley homolog of the dicot vacuolar-processing protease, is localized in nuclear cell walls. Plant Physiol 1998 118(4) 1169-1180. 

Mixed / -D-glucans are widely distributed in monocots, and they have been isolated from rye,203 oat,204-206 and barley207 endosperms, and from maize,208 barley,209 and wheat80210 stems. All of these preparations probably possessed secondary as well as primary cell-walls. 

There have been few studies of polymer interconnections within the primary wall of monocots. An arabinoxylan from the primary wall of cultured, barley-aleurone cells,61 and a glucuronoarabinoxylan from maize-coleoptile primary-wall,200 have been shown to bind reversibly to cellulose in vitro, Because xylans are, quantitatively, the major component of monocot primary cell-walls, this interconnection is an important finding it is very likely to occur through multiple hydrogen-bonds, analogous to the interconnection between xyloglucan and cellulose in dicot cell-walls.56,57,59 It is also possible that heteroxylans participate in binding other cell-wall polymers to cellulose. 

In contrast to these findings, a glucuronoarabinoxylan isolated from oat coleoptiles did not bind to cellulose in vitro under reaction conditions that allowed other heteroxylans to bind.53 This oat heteroxylan had, however, a high percentage of arabinosyl side chains that would be likely to hinder binding sterically. A similar inability to bind to cellulose is exhibited by an arabinose-rich arabinoxylan isolated from cultured, barley-aleurone cell-walls.61... 

Phenolic acids, and especially ferulic acid, which is abundantly present in cereals, is found esterified to the polysaccharides present in primary and secondary cell walls of plants. Ferulic acid is the major phenolic acid occurring in the cell walls of monocotyledons and appears as cis and the more abundant trans isomers (reviewed in [Klepacka and Forna, 2006]). Ferulic acid is found in wheat, maize, rye, barley [Sun et al., 2001], oats, spinach, sugar beet, and water chesnuts [Clifford, 1999], generally esterified, and rarely as free form, such as in barley [Yu et al., 2001]. It is esterified in primary cell walls to arabinoxylans (Fig. 2.4) in the aleurone layer and pericarp [Clifford, 1999], as in spinach [Fry, 1982] or in wheat bran [Smith and Hartley, 1983], Ferulic acid can also be found esterified to other hydroxycinnamic acids such as in Mongolian medicinal plants where it is found as feruloylpodospermic acid, which is... 

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