Plant Cell Walls : Formation and Structure

All the plant cells have cell wall which is made of cellulose. it provides the definite shape to the cell. The thickening of the cell wall is about  0.1 – 10 µm. initially it is believed that plants cell wall is a dead structure & provides security, but now it is proved that cell wall is a rigid structure that possess pores. The pores transfers signals from one cell to another cell. The plants cell wall structure is as follows :-

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Formation and Growth of  Plants Cell Wall

• The entire existing cells have the potential to divide itself to form new cell for growth of cell. The cell division is occurs in two steps – 
1. Nuclear division and 
2. Cytoplasm division.
• During the cytoplasmic division, a cell plate is formed from calcium pectate.
• Cell plate works as a base in the formation of cell wall.
• Formation of cell wall involves two process, which is responsible for the formation of secondary & tertiary cell wall -

                                    i.          Intussusceptions

• Formation of primary cell wall is done by the Intussusception.
• To form the primary cell wall of a cell ,the particles of pectose and cellulose are begin to deposed off in the molecules of calcium pectate , which is present in cell plate.
•  Primary cell wall is much smooth and elastic.
• It becomes stretched to form secondary cell wall.

                                 ii.          Apposition

• Forming new layers on pre-existing cells are called apposition.
• Firstly there is a growth in the length & width of the pre – existing cells.
• Molecules of cellulose and pectose like substances are now begin to deposed of on the blank space of the cellulose layer of primary cell wall.

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Structure of Plants Cell Wall 

There are about three layers are clear visible in all plants cell wall while the fourth layer of the cell wall is present in few gymnosperms plants cell wall and it is a matter of controversy among scientists. However the layers of cell wall is as follows –

1.       Middle lamella
2.       Primary wall
3.       Secondary wall
4.       Tertiary wall – present is few plants cell

1.  Middle Lamella

• This is made of pectin ( a cementing material of calcium & magnesium pectate ).
• It is present between the primary cells of adjacent cells.
• Binding the adjacent cells is its main function.
• It is soluble only in strong acids.

2. Primary Cell Wall

• Inside the middle lamella, there is a elastic and thin layer ( 1 – 3 µm ) of primary wall is present, which is secrets by protoplasm.
• The primary cell wall is a complex net of microfibrils.
• It is composed of mainly three elements .
•       i.          Cellulose microfibrils
•      ii.          Pectinated polysaccharides
•     iii.          Structural proteins

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• The structural unit of primary cell wall is micelle or elementary fibril.
• Near about 100 series of cellulose molecules combines to form Micelle or elementary fibril.
• About 20 micelle or elementary fibril combines to form microfibril.
• About 250 microfibrils joints through hydrogen bond to form fibril.
• Many fibrils comes together to form a continuous & complex net which is embedded in pectinated polysaccharides.
• Structural protein also makes a net system which also associates with these two net systems.
• At the time of cell development, few pores are formed in the middle lamella and primary cell wall. these pores are known as plasmodesmeta ( the name is given by Strasburger ).

Plant Cell Wall

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3. Secondary Cell Wall

• Inside of the primary cell wall, secondary cell wall is present which consists many layers. Normally thress layers S₁ , S₂ and S₃ found, in which S₂ ( middle ) layer is thick. These are also called as inner , middle and outer layers.
• The secondary cell wall is thick ( about 5 – 10 µm ) and rigid, which is composed of cellulose, hemicelluloses and polysaccharides sugers. Pectin is absent.
• The physical and chemical nature of these three layer are different from each other.
• There are intercellular space present between the fibrils, which is composed of cellulose. After the deposition of lignin, cutin, suberin, tenin, calcium compounds, wax and minerals in the inter cellular spaces, it becomes hard and rigid & easily recognized as a secondary cell wall.

4.    Tertiary Cell Wall

• It is present on the outer side of the secondary cell wall.
• It is found in few gymnosperm plants cell wall.
• However is a matter of controversy among scientists.
• Probably it the decomposition of dried residue of the cytoplasm.
• It is composed of cellulose, hemicelluloses and xylan.

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