Plant cells are eukaryotes made up of specialised cellular organelles that differ from animal cells in numerous basic ways. Plant cells often have a strong cell wall that acts to keep them upright and protects them from losing shape. To keep the plant dynamic, the plasma film, cytoplasm, and any remaining cell organelles cooperate. The water in the plant cell is held in the vacuoles, a fluid-filled membrane-bound organelle situated inside the cytoplasm. Plant cells do not get enough water under certain conditions, or there is a significant loss of water from the cell. This causes the plant cell to shrink completely, a condition known as plasmolysis.
Plasmolysis
Plasmolysis was formed from the Latin and Greek words plasma – the mould, and lusis – loosening.
Plasmolysis could be defined as the loss of water from a plant to the extent when the cytoplasm shrinks away from the cell wall. The contraction or shrinking of the protoplasm of a plant cell is induced by water loss in the cell. Plasmolysis is an example of an osmosis outcome that happens infrequently in nature. 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. The severe loss of water results in the collapse of the cell and, ultimately, cell death.
Plasmolysis Stages
The plasmolysis process is divided into three stages:
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Incipient Plasmolysis: This is the first stage of plasmolysis when water begins to flow out of the cell; initially, the cell decreases in volume and the cell wall becomes evident.
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Clear Plasmolysis: This is the following phase of plasmolysis in which the cell divider has arrived at its breaking point of withdrawal and the cytoplasm isolates from the cell divider, forming a circular shape.
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Plasmolysis Towards the End: It is the third and final stage of plasmolysis, in which the cytoplasm is totally free of the cell wall and stays in the cell’s centre.
Types of Plasmolysis
There are two types of plasmolysis:
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Convex Plasmolysis: In this type of plasmolysis, the plasma membrane and the protoplast lose excess water, which completely detaches them from the cell wall. This 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 a lack of water.
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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.
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.
Theory – Study of Plasmolysis in Epidermal Peel of Leaf
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.
Why are the leaves of the Rheo plant utilised in this experiment?
The Rheo plant’s leaves are utilised in this experiment because they have coloured cell sap that can be plainly observed using a compound microscope.
The Principle Behind the 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 it whilst blocking some harmful components. The continual passage of water molecules in and out of the cell across the cell membrane is a key feature for allowing cells to absorb water. 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 plant cells, in this case, rhoeo leaf plant cells in concentrated sugar or salt solution, and observing the water loss of the cell.
Requirements:
The Procedure of the Rhoeo Leaf Plasmolysis Experiment
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Place two glass slides on a table and then take a rhoeo leaf from the Petri dish.
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Make a fold on the rhoeo leaf in such a way that you can make a tear from the lower side of the leaf.
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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.
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Set up these epidermal peels on each glass slide.
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Using the dropper, add some sodium chloride 0.1% solution on one of the glass slides (1-2 drops would be enough).
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Use another dropper and add 1-2 drops of sodium chloride 5% solution on the other slide.
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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, have shown plasmolysis, whilst the cells where 0.1% NaCl solution was added, have become turgid.
Precautions:
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The epidermal peel should be extracted from the lower part of the rhoeo leaf.
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The peel should be moist.
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The slides should be kept dry and excess solution
should be removed using filter paper.
How Does the Water Go Across Cell Membranes?
The cell membrane isolates the interiors of the plant cell from the outside environment during the Plasmolysis process. It lets water molecules, ions, and other selected particles pass through the membrane while preventing others from doing so. Water molecules migrate in and out of cells via cell membranes, and water flow is an unavoidable result that allows cells to get water.
Plasmolysis may be easily shown in the laboratory by immersing a live cell in a high salt solution. When plant cells are immersed in a concentrated salt solution, osmosis causes water from the cell sap to escape. As a result, water passes through the cell membrane and into the surrounding medium. Finally, the protoplasm splits from the cell and takes on the form of a sphere.
Normally, Tradescantia or Rheo plant cells, Elodea plants, or onion epidermal cells are employed for this experiment because they have coloured sap that can be easily spotted and identified under the microscope.
Plasmolysis Examples
Plasmolysis is more prevalent and occurs in the most severe episodes of water loss. Here are some real-life examples of Plasmolysis:
Vegetable Shrinkage in Hypertonic Circumstances
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When blood cells are put in hypertonic circumstances, they shrivel.
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Ocean water dumps salt onto land during significant coastal flooding.
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Weedicide spraying destroys weeds in lawns, orchards, and agricultural areas. This is due to a natural phenomenon known as plasmolysis.
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When extra salt is used as a preservative in foods such as jams, jellies, and pickles, because of the increased concentration outside, the cells lose water and become less favourable to microbe development.
Deplasmolysis
When a plasmolyzed cell is immersed in a hypotonic solution (a solution with a lower solute content than the cell sap), water enters the cell due to the greater concentration of water outside the cell. The cell then expands and becomes turgid. This is referred to as deplasmolysis.
When live cells are put in an isotonic solution (both solutions contain the same quantity of solute particles), water does not move within or outside the cells. Because water flows in and out of the cell in an equilibrium condition, the cells are said to be flaccid.
Conclusion
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 takes 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 due to the water concentration outside the cell is higher. It moves from the outside to the inside of the cell since the water concentration is higher outside.