Plasmolysis could be defined as the loss of water from a plant to the extent when the cytoplasm shrinks away from the cell wall. It takes place when a plant cell is placed in a solution that has a higher concentration of solute than the concentration of solute in the cell sap. This also means the cell has lower water potential. Due to the severe loss of water results in the collapse of the cell and ultimately cell death.
There are two types of plasmolysis
Convex plasmolysis: In this type plasmolysis the plasma membrane and the protoplast loose excess water which completely detaches them from the cell wall. The results in the collapse of the cell in a process called cytorrhysis. This type of plasmolysis cannot be reversed and leads to cell death. This takes place when the plant wilts and dies because of lack of water.
Concave plasmolysis: In this type of plasmolysis the protoplasm and the plasma membrane can shrink away from the cell due to lack of water and the protoplasm starts to detach from the cell wall. Once it’s detached it is called a protoplast. Half-moon pockets can be observed within the cell as it peels from the surface of the cell wall. This process can be observed if a plant cell is put in a hypotonic solution.
Plasmolysis shows us what happens to a plant cell in stressful conditions such as lack of water. It also shows us a plant cell’s protection mechanism against plasmolysis. Some plants have a wax layer on their leaves which helps them regulate transpiration. One of the best ways we can complete a study of plasmolysis is with the rhoeo leaf experiment.
Aim of the rhoeo discolour leaf experiment: This experiment aims to study the phenomenon of plasmolysis which takes place in rhoeo plant cells. Epidermal peeling is seen when the cells are placed in hypotonic and hypertonic salt or sugar solutions.
The Principle Behind Plasmolysis Experiment in Rhoeo Leaf: The principle of this experiment goes around the fact that the plant cell membrane is semipermeable and permits water and other ion molecules to move across its whilst blocking some harmful components. In stressful situations such as low availability of water, it allows an excess amount of water to move out of the cell which if not controlled can lead to cell death. The experiment here is carried out in any laboratory by submerging plan cells in this case rhoeo leaf plant cells in concentrated sugar or salt solution and observing the water loss of the cell.
Sodium chloride 0.1% solution
Sodium chloride 5% solution
The Procedure of the Rhoeo Leaf Plasmolysis Experiment
Place two glass slides on a table and then take on rhoeo leaf from the Petri dish.
Make a fold on the rhoeo leaf in such a way that you can make a tear from the lower side of the leaf.
From the lower surface of the epidermal layer of the leaf, take two small fragments of a fine and transparent layer with the help of forceps.
Set up these epidermal peels on each glass slide.
Using the dropper, add some sodium chloride 0.1% solution on one of the glass slides. (1-2 drops would be enough)
Use another dropper and add 1-2 drops of sodium chloride 5% solution on the other slide.
Put a coverslip on the peel of both glass sides with the help of a needle and observe both under a compound microscope after 30 minutes.
Observation: After 30 minutes, you will notice that cells where 5% NaCl solution was added, they have shown plasmolysis whilst the cells where 0.1% NaCl solution was added, they have become turgid.
The plant cells which are immersed in the hypertonic salt solution or 5% NaCl solution exhibit plasmolysis. During this process, 4%- 5% of the water passes through the cell membrane into the medium. This take s place because the concentration of water inside the cell is higher than the outside of the cell. Thus, the protoplasm induces shrinkage and takes a spherical shape.
The plant cells immersed in a hypotonic salt solution or 0.1% NaCl solution become turgid as the water in the medium moves into the plant cells as the water concentration outside the cell is higher and moves from the outside to the inside of the cell as the water concentration is higher outside.
The epidermal peel should be extracted from the lower part of the rhoeo leaf.
The peel should be moist
The slides should be kept dry and excess solution should be removed by filter paper
1. Why are rhoeo leaves taken for this experiment and can other leaves be used?
A: Rhoeo leaf cells are used in this plasmolysis experiment because the cell sap is coloured and it is visibly cleared under the microscope.
Tradescantia leaves can also be used and the solution can be changed to a sugar solution.
2. What are the stages of plasmolysis?
A: There are three stages of plasmolysis
Incipient plasmolysis: During plasmolysis, when the protoplast pulls away from the cell wall at corners, the stage is called incipient plasmolysis.
Evident plasmolysis: When the protoplast of the plant cell is completely detached from the cell wall, the stage is called as evident plasmolysis.
Final plasmolysis: When the cytoplasm of the plant cell is found at the centre of the cell, the stage is known as final plasmolysis
3. What are turgor and wall pressure?
A: Turgor pressure: The hydrostatic pressure that rises within the cell because of endosmosis and presses the plasma membrane against the cell wall is called turgor pressure.
Wall pressure: Due to turgor pressure on the rigid plant cell wall, it causes the plant cell wall to exert equal pressure in the opposing direction. This is called as wall pressure.
4. What is the importance of plasmolysis?
A: Plasmolysis is the response of a plant cell against a hypertonic. It leads to the detachment of the protoplasm from the cell wall. When plasmolysis occurs, the space between the cell wall and the protoplasm becomes filled with solutes. In turn, water diffuses to this area.
The partial detachment of protoplasm from the plant cell wall indicates that the plant needs to resolve this issue and thus the plant takes in water from the root system to prevent further water loss via transpiration. Thus, plasmolysis has is benefits as if informs the plants' internal systems that the plant body needs water.