Pectin, Lignin and Disease Resistance in Brassica napus L.: An Update
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Abstract:
The plant cell wall is dynamically modified during host–pathogen interactions and acts as a crucial factor controlling plant immunity. In the context of recently revised models of plant primary cell walls (PCWs), pectin is considered to be important in determining the mechanical properties of PCWs. A secondary cell wall is present in some cell types and lignin is normally present and acts to strengthen wall rigidity. In this review, we summarize the recent advances in understanding cell-wall-mediated defense responses against pathogens in Brassica napus L. (B. napus). A major part of this response involves pectin and lignin, and these two major cell wall components contribute greatly to immune responses in B. napus. Crosstalk between pectin and lignin metabolism has been detected in B. napus upon pathogen infection, suggesting a synergistic action of pectin and lignin metabolism in regulating cell wall integrity as well as wall-mediated immunity. The transcriptional regulation of cell-wall-mediated immunity in B. napus along with that in Arabidopsis is discussed, and directions for future work are proposed for a better understanding of wall-mediated plant immunity in B. napus.Keywords:
Pectin
Plant Immunity
Studies with normal, mutant, and transgenic plants have not clearly established whether the proportion of p-hydroxyphenyl (H), guaiacyl (G), and syringyl (S) units in lignin directly affects the degradability of cell walls by hydrolytic enzymes. Dehydrogenation polymer−cell wall complexes containing varying ratios of H, G, and S lignins were formed by peroxidase/H2O2-mediated polymerization of p-coumaryl, coniferyl, and sinapyl alcohols into nonlignified walls isolated from cell suspensions of maize (Zea mays L). Lignification substantially reduced the degradability of cell walls by fungal hydrolases, but degradability was not affected by lignin composition. On the basis of these results, we propose that improvements in wall degradability, previously attributed to changes in lignin composition, were in fact due to other associated changes in wall chemistry or ultrastructure. Keywords: Gramineae; Zea mays; cell wall; brown midrib; transgenic; O-methyltransferase; hydroxycinnamyl alcohols; lignin; cellulase; degradability
Guaiacol
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Secondary cell wall
Primary (astronomy)
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Pectin
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Pectin
Hemicellulose
Plant cell
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Hemicellulose
Secondary cell wall
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This chapter examines some of the observed empirical relationships of lignin concentration and composition with cell wall digestibility. It emphasizes information regarding molecular aspects of cell wall lignification and mechanisms by which these factors may limit bacterial fermentation and enzymatic hydrolysis of forages. For the purposes of this chapter, core lignin is considered to be the phenylpropanoid polymer deposited in the cell wall from polymerization of cinnamyl alcohols during secondary wall thickening. Composition of the core lignin polymer has been discussed as a factor which influences degradability of cell wall polysaccharides. Pyrolysis is a methodology that is currently seeing increased use for analysis of lignin structure in forages. Inferences regarding relationships of lignification to cell wall degradability drawn from data such as presented in the preceding section must be made cautiously because cell wall composition data result from analysis of total plant herbage.
Phenylpropanoid
Secondary cell wall
Middle lamella
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Limiting
Secondary cell wall
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