Plant Cell Wall: Structure, Functions, Diagram (2024)

• A cell wall is an outer rigid semi-elastic supportive and protective layer.
• It is present around the plasma membrane.
• It provides mechanical support and helps in maintaining the shape of the plant cell.
• The cell wall is present in the plant cell and absent in the animal cell which distinguishes them from each other.
• The cell wall is formed by the protoplast. Any plant cell which is devoid of the cell wall is called the protoplast.
• The plant cell is mostly made up of the following components:
  • Cellulose
  • Hemicellulose
  • Pectin
  • Protein

• In both the primary and secondary cell walls of the plant, cellulose is present.
• Cellulose is an insoluble carbohydrate.
• The fibrous structure present in the cell wall maintains the integrity of the structure.
• In the primary cell wall, Pectin is present predominantly.
• It plays the important role in:
  • Expansion
  • Strength
  • Porosity
  • Adhesion
  • Intercellular signaling

• Other non-cellulosic polysaccharides include xyloglucan, glucan, xylan, mannan, and callose.
• Based on the sugar substitutes and side chains, pectic and non-cellulosic polysaccharides can be distinguished further too.
• During biosynthesis, these components are attached to the polysaccharides.
• These substituents are important in determining the solubility and viscosity within the cell wall.
• They are also responsible for determining the interaction between polysaccharides and proteins.
• The cell wall of fungi is made of chitin.
• The cell wall of bacteria is made of the protein, lipid, and polysaccharides complex.

Structure of Plant Cell wall

• It is derived from the living protoplast.
• It consists of the middle lamella, primary cell wall, plasmodesmata, secondary cell wall, and pits.

Middle lamella

• After the cytokinesis, it is the first-formed layer.
• It is present in between the two adjacent cells.
• It is made up of calcium and magnesium pectate.
• It helps to join the two adjacent cells.

Primary cell wall

• It is the first formed cell wall.
• It is present in the inner side of the middle lamella.
• It is the thin and permeable layer that can be expanded.
• Cutin and cutin waxes are present in some epidermal cells of the leaf and stem. It makes the primary cell wall impermeable.
• It is formed before the growth and development of the cell.
• It is made up of matrix and microfibrils.
• Matrix is made up of water, hemicelluloses, pectin, lipids, and proteins.
• Microfibrils are embedded in the gel-like matrix.
• The primary cell wall of the plant is made of cellulose.
• In the fungi, chitin makes the primary cell wall, and in bacteria murein makes it.
• Primary cell wall forms the only cell wall in the immature meristematic and parenchymatous cells.

Plasmodesma (plural: plasmodesmata)

• Plasmodesmata are cytoplasmic or protoplasmic bridges present in the primary cell wall of adjacent cells.
• They form a protoplasmic continuum called symplast.
• They transfer cytoplasmic materials among adjacent cells.

Secondary cell wall

• The secondary cell wall is situated inner to the primary cell wall.
• This is the thick layer, permeable, and cannot be expanded.
• It forms after the growth and development of the cell.
• It is present in the cells of the thick-walled dead tissue of the plant. Eg: Cells of sclerenchyma, tracheids, and vessels.
• It is differentiated into the outer layer (S₁), middle layer (S₂), and inner layer (S₃).
• Each layer is made up of a matrix and microfibrils.
• The chemical composition of the matrix is almost similar to the matrix of the primary cell.
• Microfibrils of the secondary cell wall is made up of cellulose and lignin.
• Some chemicals like suberin, silica, wax, resins, oils, etc. are also deposited in the secondary cell wall.

Pits

• In the secondary cell wall, pits are the unthickened areas or depressed areas.
• A pit consists of a pit cavity or pit chamber and pit membrane.
• The pit membrane consists of the primary cell wall and middle lamella.
• The pit membrane is permeable.
• So pit helps in rapid translocation of materials between two adjacent cells.

Tertiary cell wall

• In some plant cells, there is the presence of another cell wall beneath the secondary cell wall. It is known as the tertiary cell wall.
• The morphology, chemistry, and staining properties of the tertiary cell wall are different from the primary and secondary cell walls.
• In the tertiary cell wall, xylan is also present in it.

Functions of plant cell wall

• It provides mechanical support as the skeletal framework in the plant.
• It protects the inner components of the cell from mechanical injuries.
• It is permeable to the water and solutes. It is the presence of the water-filled channels which allows the free diffusion of water and water-soluble substances. Eg: gas, salt, sugar, hormones.
• It prevents entry of the pathogenic agents inside the cell acting as the first line of defense.
• When the cell is kept in the hypotonic solution, it prevents the osmotic bursting of the cell.
• In the cell wall, cutin, wax, silica, and suberin is present which reduces the rate of transpiration.
• The cell wall of root hairs helps in the absorption of sap from the soil.
• Walls of tracheids and vessels help in the conduction of sap.
• Middle lamella helps to join the adjacent cells.
• Plasmodesmata help in the transfer of cytoplasmic materials among adjacent cells.

Cell wall in the defense mechanism

• During the infection, oligosaccharides elicitors can be released.
• These substances can be released from the host plant’s cell wall i.e DAMPs (Damage-associated Molecular patterns) or they can be from the pathogen cell wall i.e PAMPs( Pathogen-associated Molecular patterns).
• It occurs during the process of degradation.
• In the plasma membrane, immune receptors are present which receive these elicitors.
• It then activates the defense responses of DAMP or PAMP-triggered immunity.

References

1. Verma, P. S., & Agrawal, V. K. (2006). Cell Biology, Genetics, Molecular Biology, Evolution & Ecology (First edition). S . Chand and company Ltd.
2. Houston, K., Tucker, M. R., Chowdhury, J., Shirley, N., & Little, A. (2016). The plant cell wall: A complex and dynamic structure as revealed by the responses of genes under stress conditions. Frontiers in Plant Science, 7(AUG2016), 1–18. https://doi.org/10.3389/fpls.2016.00984
3. Shakya, M., Mehta, D. K. R., Gautam, M., Pokharel, K. R., & Khanal, K. (2077). Principles of Biology (First edition). Asmita Books Publisher and Distributors Ltd.