The Plasmolysis Is the process of contraction or retraction of the protoplasm of the plant cell due to the loss of water in that cell.
This process is one of the results of osmosis. It occurs when the concentration of the outer medium contains a greater number of dissolved molecules and less water per unit volume compared to the cellular liquid.
Then the semipermeable membrane allows water molecules to flow freely, increasing the outward flow, so that the concentration of the vacuole should equal the concentration of the external medium being reduced by the loss of water. The cell membrane is reduced and separated from the cell wall.
Finally, the wall of the cell membrane is separated because the cell is plasmolized. If during this process the plant does not get water to fill the vacuole so that the cell recovers its Turgor , Most likely the plant will die.
What is Plasmolysis?
Anatomy of the cell
In order to understand plasmolysis, it is necessary to refer first to the anatomy of the cell of a plant. Each cell is constituted by a plasmatic membrane , A cytoplasm inside, and protecting this structure, a cell wall composed basically of cellulose.
All major parts of the cell work together to keep the plant active. The vacuole is found in the cytoplasm containing the Water In the plant cell.
The cell or plasma membrane separates the interior of the cell from the wall, allowing the passage of water molecules, ions or some particles through the membrane and avoiding the passage of others.
Water molecules travel in and out of the cell through the cell membranes. This flow is a necessary consequence that allows the cells to obtain water.
When cells do not receive enough water, plasmolysis occurs, the plasma membrane and cytoplasm contract and separate from the cell wall, causing the whole plant to contract.
Stages of Plasmolysis
Plant wilt observed under conditions of water scarcity is an indication of the plasmolysis of the cells. There are three stages in the plasmolisis: incipient plasmólisis, evident plasmólisis and final plasmólisis.
1- Incipient Plasmolysis
In the incipient phase of plasmolysis, the first sign of cell wall shrinkage is detected. In a turgid cell, with the proper amount of water, the plasma membrane tightens the cell wall and is in full contact with it.
When this cell is held in a hypertonic solution, water begins to move out of the cell. Initially there will be no effect on the cell wall. But as water continues to leak, the cell contracts in volume.
Even so, the plasma membrane maintains contact with the cell wall due to its elastic capacity. As the water outlet continues, the plasma membrane reaches its limit of elasticity and tears from the cell wall at the ends, maintaining contact in other regions. This is the first stage of plasmolysis.
2-Clear Plasmolysis
In this second phase, the cell under hypertonic conditions continues to lose water in the external environment and is further reduced in volume. The plasma membrane is completely torn from the cell wall and contracted.
3- Final Plasmolysis
As the exosmosis continues, contraction of the cell and cytoplasm reach the minimum limit and no further contraction in volume is possible.
The cytoplasm is completely detached from the cell wall, reaching spherical shape and remaining in the center of the cell.
Types of Plasmolysis
Based on the final form of the cytoplasm, the final plasmolysis is divided into two types: concave plasmolysis and convex plasmolysis.
Concave Plasmolysis
During concave plasmolysis, the protoplasm and plasma membrane contract and separate from the cell wall due to the loss of water. The protoplasm is transformed into protoplast once it has begun to separate from the cell wall.
This process can be reversed if the cell is placed in a hypotonic solution, which will cause the water to return to the cell again.
Convex Plasmolysis
Convex plasmolysis, on the other hand, is more serious. When a cell undergoes complex plasmolysis, the plasma membrane and protoplast lose so much water that they completely separate from the cell wall.
The cell wall collapses into a process called citorrisis. Convex plasmolysis can not be reversed and causes destruction of the cell. Essentially, this is what happens when a plant withers and dies for lack of water.
Osmosis, Plasmolysis and Turgidity
Osmosis is the passage of water through a semipermeable membrane from an area where water has a higher concentration (having less solutes) to an area where it has a lower concentration (having more solutes).
In cells, the semipermeable membrane is the cellular or plasma membrane, which normally can not be appreciated. However, when the wall and membrane are separated, the cell membrane becomes visible. This process is plasmolysis.
In their usual state, the plant cells are in a state of turgor. Thanks to the turgor, nutrient solutions move between the cells, helping the plants to stay upright and avoiding their flaccidity.
Plasmolysis and deplasmolysis
In the laboratory, you can experience osmosis by placing a living cell in a saline solution, which will cause the cellular sap to move. The concentration of water inside the cell will be greater than outside it.
Therefore, water travels through the cell membrane to the neighboring medium. Finally, the protoplasm is separated from the cell and assumes a spherical shape, resulting in plasmolysis.
When a plasmolized cell is placed in a hypotonic solution (a solution in which the solute concentration is lower than the cell sap), water travels to the cell because of the higher concentration of water outside the cell.
Then the cell swells and regains its turgidity again. This process of recovering the normal turgidity of a plasmolized cell is known as deplasmolysis.
References
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- Stadelmann"Plasmolysis and deplasmolysis". Methods in Enzymology. Volume 174, 1989 Ed. Elsevier. Available online 29 Nov. 2003 Science Direct Retrieved from: sciencedirect.com.
- Stadelmann"Chapter 7 Evaluation of Turgidity, Plasmolysis, and Deplasmolysis of Plant Cells"in: Methods in Cell Biology, Volume 2 Retrieved from: sciencedirect.com.
- Müller. "Plasmólisis"in: Manual of Laboratory of Plant Physiology IICA Biblioteca Venezuela. Retrieved from: books.google.com.