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
2. Suberization :
- 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.
3. Cutinization :
- 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.
4. Deposition of cellulose :
- 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.
5. Formation of Pectin
- 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.
6. Mucilage formation :
- 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.
7. Mineralization :
- 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.
