Lignin

Chemical structure

Lignins are polymeric consisted three monomeric types of different:

the coniféryle
the p-coumaryle
sinapic alcohols

The fraction of each Monomère varies in an important way according to:

the vegetable line (Angiosperme, Gymnosperme, etc)
the Species
the Body
the fabric

Properties and lignification

Lignin settles in the secondary Paroi some vegetable cells, thus conferring a better solidity to them, because lignin is very resistant to compression. Moreover, lignin has a capacity of proofing of the cells, because of its hydrophobicity. One thus finds lignin walls impregnated (lignified) in the fabric cells being used with the support of the plant (Sclérenchyme) or for transport of water and rock salt (Xylème).

In general, the lignified cells having become impermeable, lost to them Cytoplasme and acquire their role in the plant only once died.

Lignification is a fundamental process of the evolution of the terrestrial plants. It is it which, indeed, allows the growth in height of the vegetable ligneous family. This capacity made it possible to have a drawn up port supporting the reception of luminous energy. The whole of these acquisitions being a precondition to the conquest of the terrestrial environment . The capacity of lignin formation by the plants was installation at the beginning of the Paléozoïque (with a strong development starting from the Dévonien) and characterizes the Trachéophyte S. (see Flore of Rhynie)

Biological interest

The lignin, which is thus characteristic of the vascular plants terrestrial, also offers a barrier of protection against the microbial attack of the plant. Indeed, of share its chemical nature, lignin is a matter extremely resistant to various chemical agents and biological degradation, which explains the poor quality of highly lignified fodder.

Certain micro-organisms, in particular the Fungi known as of the white Rot of the Wood, are able to entirely digest the complex lignin - hemicellulose - cellulose (Ligninolyse) and thus to improve the food value of lignocellulosic materials.

According to an assumption of A.C Neish and C. Hébant, lignin would be a form of storage of the Excrément S of the plant. Knowing that lignin consists of phenolic compounds which are toxic in free form for the plant, the latter would have found a way of neutralizing them by storing them in the form of lignin in dead vascular cells.

Economic issues

lignins are strongly required in the firewood, having an important calorific value.
On the contrary, they are awkward for the manufacture of the Papier, persons in charge of its yellowish coloring after exposure to the sun. They are the chlorinated products contained in the substances allowing the extraction of the lignin (delignification) of the paper pulp which makes this industry polluting.
Lastly, they are little digestes and thus not very required in the culture of Fodder plants.

For the reasons evoked above, many research is in hand (primarily by genetic transformation), aiming at producing plants less rich in lignin (manufacture of the Papier), or on the contrary, with a more important lignin rate (firewood).

But, considering the importance of the production of the complex lignin - hemicellulose - cellulose on planet, it is interesting to note that approximately 25% of this renewable resource would be accessible to biotechnological processes of conversion. Thus, currently the mushrooms of the white rot are very studied because of several applications:

Installation of clean and economic processes in paper industry;

Bioconversion and production of molecules with high added value of interests agro-alimentary and pharmaceutical starting from lignocellulosic materials;

Biotraitement and valorization of lignocellulosic materials (in particular for the Cattle).

Improvement of the grounds thanks to the fragmented Wood raméal

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