Formation in cell walls

The nature and amounts of low molecular weight phenolic constituents in cell walls of graminaceous plants (grasses and cereals) are reviewed and relationships discussed between these constituents and wall biodegradability. The formation in cell walls of 4,4 -dihydroxy-truxillic acid and other cyclodimers of p-coumaric and ferulic acid is suggested as an important mechanism for limiting the biodegradability of wall polysaccharides. 

The importance of a low rate of hydroxyproline formation in cell-wall... 

These circumstances became apparent to the authors when they attempted to study the formation of KDO 8-phosphate as catalyzed by purified bacterial extracts. These extracts did not catalyze the formation of KDO 8-phosphate from D-ribose 5-phosphate, but required D-arabinose 5-phosphate as the substrate Heath and Ghalambor29 showed that the KDO 8-phosphate synthetase reaction, observed in Pseudomonas extracts by Levin and Racker, is also catalyzed by extracts from Escherichia coli strains 0 111 B4 and J-5. Rick and Osborn136 showed that the KDO 8-phosphate synthetase from a Salmonella typhimurium mutant conditionally defective in cell-wall synthesis had a KM of 6 mM as compared to a KM of 170 pM for the enzyme from wild-type cells. 

All of the enzymes responsible for formation of cell-wall polysaccharide appear to be membrane-bound, and are usually recovered in the particulate, cell-wall fraction sedimenting at 20,000g none have been purified significantly. Several names have been given to these complex enzyme-systems, which may possess more than one activity, including polysaccharide synthase and glycosyltransferase. The term polysaccharide synthase is preferred for use in this article. 

The plasma membranes of plant cells possess several redox activities that can be related to both plant nutrition and cell wall formation and lignification (Liithje et al., 1997 Berczi and Mpller, 2000). In this context, it has been shown that in oat roots, HMS humic fractions inhibited NADH oxidation in either the presence or absence of an artificial electron acceptor (ferricyanide), whereas LMS fractions inhibited this oxidase only if the electron donor (NADH) and acceptor (ferricyanide) were added at the same time (Pinton et al., 1995). While the first effect could be related to the activity of surface peroxidases that can be involved in cell wall formation and thickening (Vianello and Macri, 1991), the second seems to be exerted on a different redox system with an unknown function (Nardi et al., 2002). 

Certain changes in appearance of the appressoria were noted however, the function of the appressoria was not influenced (7). Treatment did not affect the formation of the infection peg. Additionally, there was no influence of the treatment on the formation of cell wall appositions, termed papillae, which are produced by the host plant in response to the fungus beneath the site of penetration. 

Inhibits the enzymes alanine racemase and D-alanyl-D-alanyl synthetase that are responsible for producing the dipeptide D-alanyl-D-alanine, a precursor of the pentapeptide chain in cell wall formation. It is believed that the rigid structure of the isoxazole ring gives the drug a better chance of binding to the enzyme than the more flexible structure of D-alanine. 

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