Thickening & Function Of Plants Cell Wall

Plants cell wall thickening provides strengthening to the tissues, structural support, enabling upright growth, enhancing resistance to environment. it allows plants to withstand gravity, maintain their shape and protect themselves from damage caused by various factors such as pathogen, insects, extreme temperature etc.

Thickening of Cell Wall

Thickening of the cell is oftenly done after the cell development. “The process of deposition of substances on the cell wall after cell development, is called as thickening of cell wall. This process is occur only in those cells whose function is transportation and to provide mechanical support. Thus the thickening of cell wall is found in vessels and tracheids cells.

Various types of substances are deposed off on the cell wall , by which it is classified into following category –

1. Lignification

The deposition of lignin molecules layer in the cellulose layer of cell wall , is known as Lignification.
Lignin is a complex chemical substances, which is a composition of Aldehydes and Alcohols group.
Lignin is permeable for water and water soluble substances.
It is found in primary and secondary cell wall of woody plants.
Due to lignin the cell becomes thick , dead and woody, which provide mechanical support to the plant.

2. Cutinization

In this cellulose and pectin are converted into cutin.
Cutin is a wax like ( lipid ) substances, which forms a continuous covering on the outer surface of the epidermal cells of the aerial parts of the plants, which is called as cuticle.
Cuticle is impermeable for water, thus they reduce the vaporization rate from plants surface.
In succulent plants, it is thick in comparison to other plants.

3. Suberinization

It is also a lipid like substance.
The deposition of suberin in cell wall is called as suberinization.
Suberin is also impermeable for water, thus they also reduces the vaporization rate from the surface.
The cork cells are suberinised which is used to tap the mouth of bottles.

4. Chitinization

Chitin is found in few algae and mostly in fungi. This is absent in higher plants.
It is formed by the deposition of chitin and process is known as chitinization.
In insects , it forms external skeleton.

5. Silicolization

This is found mainly in the grass plants of the family Gramini.
In this the silica is deposed of in the lesfs of the grass, wheat, maize, sugarcane in the stem of equisetum.
It provides security to the plants.

6. Mineralization

When various types of minerals became deposed off in the cell wall, this is known as mineralization.
Calcium carbonate, calcium oxalate, sand particles etc. are the main elements.
Calcium carbonate particles are found in the form of bunch of grapes in banyan tress and Indian resin tress.

7. Mucilaginous Substances

Mucilaginous substances are the transformation of cellulose into mucilage.
Mucilage absorbs the water and after swallow it forms viscous substances which have the capacity to holds water.
It is found in the fleshy leafs of xerotrophic plants, china rose’s leaf and in the flower of ladyfinger.

Types of Thickening

There are mainly five types of thickening, which is the results of deposition of ligin in the cell wall. They are as follows –

A. Annular

In this the deposition of lignin is occur in the inner surface of cell wall in a ring form.
This is mainly found in the vessels and tracheids of the protoxylem.

B. Spiral

This thickening is also found in vessels and tracheids cells of protoxylem.
The deposition of lignin in the inner surface of cell wall occurs in the spiral form.

C. Scalariform or Ladder Like

The deposition of lignin forms strip or rod like shape in transverse form. they are parallel to each other and looks like a ladder.
Types of Thickening
(A) Annular (B) Spiral (C) Scalariform (D) Reticulate
(E) Simple Pit (F) Bordered Pit

D. Reticulate

When liglin is deposed in a crossed strip and each strip is jointed to each other to form a web, then it is called reticulate.

E. Pitted

In this deposition of lignin forms a continuous layer on plants cell wall, in which pore like structures are found. Due to the pore like structures, it is called as pitted.
These pore like structure are called pits.
Usually pits are formed in pairs on both sides of the wall separating two adjacent cells. Thus these pits are called pit pairs.
The thin primary wall separating the pairs of pits is called pit membrane.
Sometimes Pits are formed only one side of the wall, then it is called as blind pits.
The diffusion of fluids is helds through the pits successfully.
There are two types of pits , which is as follows -

i. Simple Pit

These are normally rounded or oval shaped.
These are founded in thick walled parenchyma.
The depth of all simple pit are equal.

ii. Bordered Pit

The pit membrane of Bordered pit is formed by the middle lamella and the primary cell wall of two adjacent cells.
The pit membrane swallows after thickening to form torus which controls the diffusion of fluids of adjacent cells.
These are normally found in vessels and tracheids.
The depth of all bordered pit is not equal.
Pit forms funnel or dome like structure on going deeper into the cell from cell wall to pit membrane.
Both type of shape, rounded or oval, are found in the same cell.

Function of Plants Cell Wall

Plants cell wall provides definite shape and rigidity to the cell.
It protects from external injuries.
It provides the mechanical support to the plants , by which plants parts stands in a way to absorb the sunlight.
In the absorption of excess water through osmosis in the cell, it stops the expansion of cell. Thus the cell is not becomes raptured.
Suberin and cutin reduces the vaporization rate from the plants.
Plasmodesmata and pits of the adjacent cells are helpful in the transportation of cytoplasm & essential substances.
A fully developed cell stops the excess growth of the cell.
It protects the cell drying out.

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