Monolignols, also called lignols, are the source materials for biosynthesis of both

lignans The lignans are a large group of low molecular weight polyphenols found in plants, particularly seeds, whole grains, and vegetables. The name derives from the Latin word for "wood". Lignans are precursors to phytoestrogens. They may play a role ...

and lignin and consist mainly of

paracoumaryl alcohol Paracoumaryl alcohol is a phytochemical, one of the monolignols. It is a white solid. ''p''-Coumaryl alcohol is a major precursor to lignin or lignans. Biosynthesis and occurrence It is synthesized via the phenylpropanoid biochemical pathway. E ...

(H),

coniferyl alcohol Coniferyl alcohol is an organic compound with the formula HO(CH3O)C6H3CH=CHCH2OH. A colourless or white solid, it is one of the monolignols, produced via the phenylpropanoid biochemical pathway. When copolymerized with related aromatic compounds, ...

(G) and

sinapyl alcohol Sinapyl alcohol is an organic compound structurally related to cinnamic acid. It is biosynthetized via the phenylpropanoid biochemical pathway, its immediate precursor being sinapaldehyde. This phytochemical is one of the monolignols, which are ...

(S). These monolignols differ in their degree of methoxilation of the aromatic ring. The monolignols are derived from the

amino acid Amino acids are organic compounds that contain both amino and carboxylic acid functional groups. Although hundreds of amino acids exist in nature, by far the most important are the alpha-amino acids, which comprise proteins. Only 22 alpha a ...

phenylalanine via the phenylpropanoid pathway involving various enzymes. Phenylalanine is first converted to

(H), which is subsequently elaborated to

(G) and

(S). This reaction happens in the

cytosol The cytosol, also known as cytoplasmic matrix or groundplasm, is one of the liquids found inside cells (intracellular fluid (ICF)). It is separated into compartments by membranes. For example, the mitochondrial matrix separates the mitochondri ...

, while the polymerization of the monolignols occurs in the

apoplast Inside a plant, the apoplast can mean the space outside of cell membranes, where material can diffuse freely; that is, the extracellular spaces. ''Apoplast '' can also refer especially to the continuum of cell walls of adjacent cells; fluid and ...

to which the monolignols have to be transported to though the

cell membrane The cell membrane (also known as the plasma membrane (PM) or cytoplasmic membrane, and historically referred to as the plasmalemma) is a biological membrane that separates and protects the interior of all cells from the outside environment ( ...

. The monolignols have been found as monolignol-4-O-β-d-

glucoside A glucoside is a glycoside that is derived from glucose. Glucosides are common in plants, but rare in animals. Glucose is produced when a glucoside is hydrolysed by purely chemical means, or decomposed by fermentation or enzymes. The name was o ...

s, which might be their major way of storage. Another theory for this conversion is that is improving the transportation of the monolignols. The polymerization consists of oxidative coupling reactions, which occur between the propenyl substituens, two aromatic rings or a propenyl subsituent and a ring. The difference between lignans and lignin is the number of monolignols they are composed of. Lignans are typically dimers and therefore soluble and susceptible to biodegradation. Lignin is a polymer with an inert nature that forms the structures of woody plants. The ratio of the three monolignols as well as their linkages varies depending on the

plant Plants are predominantly photosynthetic eukaryotes of the kingdom Plantae. Historically, the plant kingdom encompassed all living things that were not animals, and included algae and fungi; however, all current definitions of Plantae exclud ...

species. For example, Norway spruce lignin is almost entirely derived from

, whereas

is the main monomer of lignin in

grass Poaceae () or Gramineae () is a large and nearly ubiquitous family of monocotyledonous flowering plants commonly known as grasses. It includes the cereal grasses, bamboos and the grasses of natural grassland and species cultivated in lawns an ...

es. Even within one plant, the monomer composition of lignin can vary depending on the part of the plant and other phenolic compounds can be found as monomers in lignin. The

phenylpropene Phenylpropene is the organic compound with the formula C6H5CH2CH=CH2. It is a colorless liquid. The compound consists of a phenyl group attached to allyl. Phenylpropene isomerizes to trans-propenylbenzene. In plant biochemistry, the phenylpro ...

s are derived from the monolignols.

References

{{Phenylpropanoids