Chemical Modification of Cell Wall

In almost all plants cell walls are mainly made up of cellulose.
But to provide mechanical support other cellular substances viz, lignin, cutin, suberin, pectin and mineral are also deposited.
So the cell wall becomes chemically modified.
The following conditions may occur in cell wall after primary wall formation.
It is the following type-

1. Lignification:

Lignin is a complex and hard substance which makes their delicate primary wall lignified, thickened, rigid and hard together with cellulose.
Lignin Is impermeable to water.
Those cells which undergo lignification, are dead, and provide mechanical strength.
The protoplasm of lignified cells ultimately is lost completely for example vessels, tracheids and sclerenchyma etc. a

It is a mixture of many fats.
It is produced by the condensation of glycerol and phenolic acids. Which is impermeable to water.
Suberin normally accumulates at middle lamella. This process is called suberization.
By the deposition of suberin cell are dead.
It is found in Cork cells and casparian srips.

It is a waxy material which is an anhydrous form of fatty acids.
It is also impermeable to water
This is present on epidermis of aerial parts of plants as a single layer. This layer is called cuticle. The accumulation of cuticle or its formation is called cutinization
It helps In prevention of evaporation.
Sometimes a wavy layer is formed over the cuticle called bloom which also controls evaporation.
The thickness of cuticle varies in all plants according to the environment.

The wall of plant cells are formed initially by cellulose. But some time it is thickened by the cellulose
For example, collenchyma and cotton fibres are made from cellulose.

After the fruit ripen the chemical composition of cell wall is changed.
In these cells Middle lamella is composed of Ca and Mg Pactat and Primary cell wall and Secondary cell wall are composed of cellulose and pactose.
After the ripen of fruit pectin is formed in these cell walls which are soluble.

In certain conditions cellulose is decomposed into mucilaginous substance which is called mucilage.
It has the ability to absorb water hence it is converted into viscous fluid by absorbing water.
The cell wall of leaves of Aloe Vera, Chinarose, fruits of lady finger, isabgol etc. possess a major content of mucilage in them.

Minerals and salts such as silica, calcium carbonate, calcium oxalate etc are accumulated in plant cells so that cells become rigid.
Silica is found in high amounts in equisetum plants (Pteridophyta) and grass leaves.

8. Deposition of other substances: Substance like resin and tanin are present in some plants.