Monolignols, also called lignols, are the source materials for

biosynthesis Biosynthesis is a multi-step, enzyme- catalyzed process where substrates are converted into more complex products in living organisms. In biosynthesis, simple compounds are modified, converted into other compounds, or joined to form macromolecule ...

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 (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 ar ...

(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 am ...

phenylalanine via the phenylpropanoid pathway involving various enzymes. Phenylalanine is first converted to paracoumaryl alcohol (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 mitochondrio ...

, 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 ma ...

to which the monolignols have to be transported to though the cell membrane. 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 species. For example,

Norway spruce ''Picea abies'', the Norway spruce or European spruce, is a species of spruce native to Northern, Central and Eastern Europe. It has branchlets that typically hang downwards, and the largest cones of any spruce, 9–17 cm long. It is very clo ...

lignin is almost entirely derived from

, whereas paracoumaryl alcohol 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 and ...

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 phenylpropenes are derived from the monolignols.

References

{{Phenylpropanoids