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Central Vacuole

Central Vacuole Definition

To put it simply, the central vacuole is membrane-bound organelle that can be seen in the cells of the following organisms:

  • Plants
  • Fungi
  • Protists
  • Animals
  • Bacteria

Until recently, it has been believed that all the vacuoles that are present in all these types of cells have a common origin. But, the recent research studies have found out that the vacuoles present in different organisms are different. For example, let’s take the plant cells. In these cells, there will be a large central vacuole. As such, the large central vacuole in the plant cells is found to be occupying a major portion of the cell mass, as well as the cell volume. It is to be noted that the presence of central vacuole is significant for the physiology of the entire plant.

Types of Plant Vacuoles

Fundamentally, the plant vacuoles are of two types, which are namely, protein storage vacuoles and lytic vacuoles. It is to be noted that these two types represent two separate organelles in the plant cell as these are found to be mediated by different transport vesicles.

Protein storage vacuoles

As the name suggests, these are used to store various proteins that are essential for the overall growth of the plants. Examples of proteins that are stored by these vacuoles are defense and storage proteins.

Lytic vacuoles

These, on the other hand, will be composed of hydrolytic enzymes, which are meant for digesting the cell components that are no longer useful.

Central Vacuole Structure

When structurally seen, the central vacuole and the other vacuoles are found to be made up of the “phospholipid bilayer”. Unlike the other types of cells, the plant cells have a larger vacuole, which has two components in its structure. They are:

Cell sap

This is the liquid portion of the central vacuole and is made of the following constituents:

  • Sugars
  • Amino acids
  • Lipids
  • Mineral salts
  • Pigments

Tonoplast

This is the membrane that covers the cell sap, thereby, separating the sap from the cytoplasm. This membrane will help give the tension on the central vacuole. Just like the cell membrane that is found in the outer layer of the plant cell, this membrane is also made up of phospholipids and proteins. These proteins will regulate the entry and exit of water in the central vacuole, which will also regulate the movement of ions.

Central Vacuole Functions

The major functions of the central vacuole are as follows:

Turgor Pressure Maintenance

As mentioned above, the central vacuole can occupy up to 90% of the cell volume. Thus, it plays a significant role in maintaining the turgor pressure, which is defined as the pressure that will be exerted by the cell components on the cell wall. As such, the amount of water that is present inside this organelle will determine the amount of pressure to be exerted.

Storage

As one can find above, one of the types of vacuoles is the storage vacuole, which would store the chemical products (protein storage vacuoles). This function of the central vacuole is seemed to be evident in the plants that depend mainly on the storage of food inside the vacuole. Examples include bulbs, rhizomes, and tubers.

Defense

As one might be aware already, plants don’t have the so-called immune cells for defense. In contrast, they have defense cell death mechanisms. These are two types of mechanisms in which vacuoles are involved in the defense.

  • Destructive mechanism: This would occur when the vacuole’s membrane collapses, thereby, releasing the enzymes to destroy the cell components. This action would lead to the immediate death of the cell.
  • Non-destructive mechanism: In this, the vacuole’s membrane would fuse with the plasma membrane to release the enzymes required for cell death.

Gas Exchange

In plants, gas exchange, which is also called as respiration is governed by the vacuoles. The special kind of cells, known as guard cells, will be responsible the opening and closing of the stomatal pores. By regulating the intake of water inside its membrane, the vacuole of the guard cells will control the respiration process.

Plant Locomotion

Some plants have the ability to move. In such plants, the central vacuole will play an important role in the locomotion by controlling the activity of the tonoplast to take or lose water.

Cell Growth

The central vacuole is able to provide help in the cell elongation process by creating a higher hydrostatic pressure. But, it’s to be noted that this can only occur when the cell wall becomes soft and elastic.

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