Biosynthetic pathways lignin

Isherwood, F. A. Bio.synthesis of Lignin. In Pridham, J. B., and T. Swain (Editors) Biosynthetic Pathways in Higher Plants. Academic Press, London-New York, 1965. 

Cellulose, hemicelluloses, and lignin are the main components of cell walls in woody plants. For a long time, these plant polymers have stimulated the interest of many plant botanists and biochemists in terms of their biosynthetic pathways, functional interrelationships, and anatomical distribution. 

In a recent study (54), we showed increased activities of two enzymes of the general phenylpropanoid pathway, PAL and 4-coumarate CoA lig-ase, as well as one enzyme of the specific pathway of lignin biosynthesis, cinnamy 1-alcohol dehydrogenase (CAD), in resistant plants at the time of the hypersensitive host cell death. On the other hand, decreased activities were observed at the same time with susceptible host plants (54). Furthermore, we showed that the well known increase in peroxidase activities, which is strong in resistant and only weak in susceptible plants (55-58), is at least partly due to the increased activity of the lignin biosynthetic pathway (54,59). 

Lacombe, E., Hawkins, S., Van Doorsselaere, J., Piquemal, J., Goffher, D., Poeydomenge, O., Boudet, A.-M., and Grima-Pettenati, J., 1997, Cinnamoyl Co A reductase, the first committed enzyme of the lignin branch biosynthetic pathway cloning, expression and phylogenetic relationships, Plant J. 11 429-441. 

Comprehensive information on the network of pathways responsible for the synthesis of numerous secondary metabolites can be found in Chapter 21. In addition, information on this aspect is also available in articles by Shimada et al. [2003], Toshiaki [2003], Tanner et al. [2003], Boatright et al. [2004], Hoffmann et al. [2004], Dixon et al. [2005], Niemetz and Gross [2005], Xie and Dixon [2005], and Ferrer et al. [2008], Nonetheless, the complete dissection of phenolic metabolic pathway is far from being complete. For example, recent reports underline that important questions still remain to be answered in the field of protoanthocyanidins and tannins [Xie and Dixon, 2005], and that the exact nature of the biosynthetic pathway(s) leading to lignin monomers has not been fully elucidated [Boudet, 2007]. 

Phenolic compounds and flavonoids are a unique category of plant phytochemicals especially in terms of their vast po ential health-benefiting properties. They represent the most abundant and the most widely represented class of plant natural products. A substantial amount of research has been carried out over the past two decades yet large information gaps still exist. For example, the inventory of these compounds is still incomplete, although there is continuous effort to provide new structures. In addition the dissection of the metabolic pathways for certain phenolic compounds remains to be resolved. Recent reports underline that important questions that still need to be answered in the field of proanthocyanidin and tannin biosynthesis [Xie and Dixon, 2005], and even the exact nature of the biosynthetic pathway(s) leading to lignin monomers is not fully elucidated. 

Legay S, Lacombe E, Goicoechea M, Briere C, Seguin A, Mackay J, Grima-Pettenati J. 2007. Molecular characterization of EgM YB1, a putative transcriptional repressor of the lignin biosynthetic pathway. Plant Sci 173 542-549. 

As briefly described above, proposed biosynthetic pathways to the monolignols follow a metabolic grid, with a number of parallel and redundant pathways for the synthesis of the major lignin components, namely guaiacyl and syringyl units. Currently, the methylation steps in the lignin biosynthetic pathway are believed to follow two main branches dependent on COMT and CCoAOMT,... 

Phenylpropanoids have an aromatic ring with a three-carbon substituent. Caffeic acid (308) and eugenol (309) are known examples of this class of compounds. Phenylpropanoids are formed via the shikimic acid biosynthetic pathway via phenylalanine or tyrosine with cinnamic acid as an important intermediate. Phenylpropanoids are a diverse group of secondary plant compounds and include the flavonoids (plant-derived dyes), lignin, coumarins, and many small phenolic molecules. They are known to act as feeding deterrents, contributing bitter or astringent properties to plants such as lemons and tea. 

Chen, R, Yasuda, S. and Fukushima, K. (1999) Evidence for a novel biosynthetic pathway that regulates the ratio of syringyl to guaiacyl residues in lignin in differentiating xylem of Magnolia kobus DC. Planta, 207, 597-603. 

Yamauchi, K., Yasuda, S., Hamada, K., Tsutsumi, Y. and Fukushima, K. (2003) Multiform biosynthetic pathway of syringyl lignin in angiosperms. Planta, 216, 496-501. 

Lignins in Monolignol-Biosynthetic-Pathway Mutant or Transgenic Plants... 

Note Data is presented to show how 2D correlation chemical shifts of acetylated lignins in acetone-d (unless denoted with a superscript c) from various 2D spectra (author-generated from various in-house sources) can be used as a guide for assigning COSY, TOCSY, HMQC/HSQC, HMQC/ HSQC-TOCSY, HMBC, etc. spectra, the author-generated data include components that may be easily seen only in various lignin-biosynthetic-pathway mutants and transgenics. 

Marita, J. M. (2001) Lignin in Lignin-Biosynthetic-Pathway Mutants and Transgenics Structural Studies. Ph.D., U. Wisconsin-Madison (University Microfilms International 3012586). 

Gang, D. R., Fujita, M., Davin, L. D., and Lewis, N. G. (1998) The abnormal lignins mapping heartwood formation through the lignan biosynthetic pathway. In Lewis,... 

Further studies about the biosynthesis of SA have been carried out in rice (Oryza sativa). In agreement with the SA biosynthetic pathway in tobacco, SA is synthesized from CA via BA. In addition to the conversion of [ C]-CA into SA, it is also transformed to the lignin precursors /7-coumaric acid and ferulic acid. [" C]-benzoic acid was readily converted to SA [32]. 

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