Middle Lamella Function: What, Structure FAQs

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The middle lamella is structurally the last outer layer of the plant cell wall.

Plant cells wall is made up of three layers in total, among which the middle lamella is the outermost layer lying in contact with other cells or the environment.

The middle lamella is what connects one adjacent plant cell to another, by forming a cement or jelly-like connective layer. This layer is what allows the cells to communicate with one another and share information and materials by the formation of something called the plasmodesmata.

What is middle lamella?

Essential in plant physiology middle lamella is a special material that joins adjacent plant cells.

Neighboring plant cells adhere or attach to the cells beside or adjacent to them via the middle lamella. The cell wall is composed of three layers among which the middle lamella is the one that is on the outermost edge.

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Structure of the cell wall showing the middle lamella
Image: Wikipedia

The middle lamella is high in pectin binding the neighboring cells’ main cell walls together. It stabilizes the cells and forms plasmodesmata(small channels that allow adjacent cells to communicate or share materials) between them. The middle lamella is the first layer to be formed from the cell plate splitting the two sister cells, during plant cell cytokinesis.

Middle lamella structure:

  • The plant cell wall is composed of 3 layers-Primary cell wall. Secondary cell wall and the middle lamella. 
  • The primary cell wall is the innermost layer lying in contact with the plasma membrane, while the middle lamella is the outermost layer in contact with adjacent cells or the out environment. The secondary cell wall is sandwiched in between these 2 layers.
  • The middle lamella is essentially composed of peptic polysaccharides just like the cell wall. If the cell is the outermost cell, the middle lamella can also have lignin in its composition for bark formation.
  • The pectins are mainly composed of Calcium and magnesium pectates
  • These polysaccharides are synthesized by the Golgi bodies and transported to the outer layers of the cell wall via exocytosis.
  • Using antibody staining it has been determined that in mature cells the pectins in the middle lamella are partially esterified.
  • The presence of hydroxyproline-rich glycoproteins found only in the cell junctions of the middle lamella is another hallmark of its chemical makeup.

Middle lamella function:

The middle lamella has several functions that can be classified mainly into- mechanical support and cell communication.

Mechanical and structural functions:

  • The intermediate or middle lamella acts as a cementing layer between the major walls of neighbouring cells.
  • The plant cell’s cell wall shields it from mechanical stress. The cell wall offers strength, rigidity, and protection to plant cells, particularly against osmotic lysis.
  • The middle lamella is a portion of the cell wall that connects neighbouring cells. 

Cell communication:

  • Being the outermost layer of the cell wall, they allow the cell to communicate with adjacent cells and the environment.
  • This communication includes the exchange of gases, cellular materials, nutrients and also information.
  • This mainly occurs via plasmodesmata- small pores in the middle lamella that act and channels for the byway transport of materials.
  • As the middle lamella is degraded by enzymes like in the ripening of fruits it allows the cells to separate from each other.
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Transport of materials via plasmodesmata Image: Wikipedia

How does middle lamella work?

The main job of the middle lamella is to adhere adjacent cells to one another.

The middle lamella’s primary role is to hold neighbouring cells together. Pectin makes up the central lamella, which functions as a gelling agent or glue to keep the plant together.

Plant Cell Wall
Placement of the middle lamella Image: Wikipedia

Adhesion of neighbouring cells is the function of the intermediate lamella in basic words. The middle lamella is a section of the cell wall that links neighbouring (similar or different) cells to form a compact and stable tissue structure. It also facilitates cell communication by forming plasmodesmata between them.

Why middle lamella is optically inactive and amorphous?

The middle lamella of the cell wall is chemically amorphous and optically inactive.

The middle lamella of the cell wall is mainly composed of Calcium pectate, Magnesium pectate, Calcium Carbonate, Calcium Oxalate along with some lignin. The composition of the middle lamella lamella makes it amorphous in nature.

Due to the presence of pectates and proteins, the middle lamella is also optically inactive or isotropic. This is mainly because it is made up of inorganics salts rather than large carbon associated molecules that lack the ability to rotate the plane of plane-polarized light directed at it.

This is very different from the cell wall that is anisotropic or optically active. It may be due to the fact that unlike the middle lamella it is composed of long-chain polysaccharides like cellulose pectin(in the case of bacteria)

Why is the middle lamella of the cell wall important?

The middle lamella is simply an important aspect of plant physiology.

It functions in varied ways to hold the cell compactness together. It helps to keep the cells structure stable by attaching adjacent cells to each other. Not only cells that are side by side but also those above and below the line.

The compact structure of plant tissues are complex and require the cementing property of the middle lamella to keep them stable. A single plant tissue can have more than one type of cell with different structures that must remain attached to each other tightly to allow the passage of water or food molecules from one part of the plant to another.

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Structure of plasmodesmata
Image: Wikipedia

 The middle lamella also forms plasmodesmata or small pores that form channels that allow the above transport to function flawlessly. This is because the cell wall is quite rigid which makes it difficult for the exchange of materials possible through it. Without the presence of the plasmodesmata processes like- water transport, food storage and transport or guttation would not be possible in plant systems.

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