When it comes to learning about plant cells, there are various components, each working in tandem to sustain the plant itself. Vacuoles are no different and serve many specific functions that we’ll go into in-depth in this article.
Vacuoles are organelles – also known as ‘little organs’ because of the fact that they perform specialized functions within a cell – which have many different functions.
They are bound by membranes and have some of the same characteristics as lysosomes, also found in plant cells.
So what else do vacuoles do that makes them so unique and essential? How do they develop over time?
What do they look like when observed under the microscope? Well, if you want to know more about this amazing organelle, then we would suggest that you keep reading.
Vacuoles – Some Of The Basics
When it comes to vacuoles, they are very multifunctional, having different jobs depending on which plants they happen to be found in. Each of these different vacuoles has certain properties that help each specific plant.
As we mentioned above, these vacuoles have some of the same properties of lysosomes that can be found in animals.
Lysosomes are responsible for the breaking down and absorption of various nutrients, as well phagocytosis, which is the ingestion of bacteria.
Vacuoles, on the other hand, serve numerous different functions in the cell that a lysosome does not. They also contain molecules, excretions, pigments and water, which lysosomes also do not.
Vacuoles can also be found in much more abundance in each cell, making up around 80-90% of its entire composition.
But how do these micro-cellular organelles operate inside the cell and how do they develop? Keep reading to find out more.
Vacuoles are very mysterious things and not a lot is known about their biogenesis.
Biogenesis, as you might have already guessed, is how living matter is made from more living matter. This is literally how things such as vacuoles come into being.
There are numerous studies that hint at vacuoles that develop in the root tip first arise from vesicles.
Vesicles are also small structures within a cell. These are mainly made from a liquid that is enclosed in a layer of lipid membrane. These structures help with transportation around the plant, control of buoyancy and storage of certain enzymes.
The vesicles that give rise to vacuoles are said to come from Golgi bodies.
Golgi bodies are also organelles that are responsible for packaging proteins into vesicles that are then transported around the body of the plant. They are considered a complex of vesicles.
When the fusion of vesicles occurs, it starts the process of prevacuole production. There are the structures that later turn into vacuoles proper. This is when multiple prevacuoles cluster together and eventually fuse.
But what kind of vacuoles are there and what purpose does each one serve within a plant?
Types Of Vacuoles And What They Do In The Body
These are the vacuoles that have the most in common with lysosomes that we mentioned earlier.
The similarity lies in the fact that they have various strands of hydrolytic enzymes that help break down nucleic acids, polysaccharides and proteins, which are distributed through the body of the plant using other organelles.
Lytic vacuoles are very mysterious like a lot of other types of vacuoles. However, it is suggested that these structures also come from the trans-Golgi complex.
If you were to evaluate the pH level of these types of vacuoles, then you would see that they have a value of around 5, making them moderately acidic.
There are a lot of different types of enzymes that are contained within a lytic vacuole, each one is responsible for breaking down and dividing various molecules and chemical bonds. Here is a list of a few of them:
- Esterases – these enzymes are responsible for breaking down esters, which are acid and alkyl compounds. They contain hydrolase enzymes that are specifically designed to break down esters into acids and alcohol groups.
- Peroxidases – these types of enzymes usually come from the disintegration of hydrogen peroxide, which causes it to be taken out of chloroplast and cytosol in various plants.
- Nucleases – these are enzymes whose job it is to break up the phosphodiester bonds that produce nucleotides.
- Hydrolases – These are types of enzymes that utilize water to break down certain chemical bonds, by which they can organize larger molecules, splitting them up into smaller molecules.
Plants, like a lot of living organisms, have different processes through which they get rid of unwanted matter from the plant itself. This can be either cytoplasmic material or even an entire cell itself.
Autophagy is one of the main processes that occur to get rid of this unwanted matter. Here is a brief explanation of what autophagy is and why it’s so effective.
What Is Autophagy?
Autophagy might sound like a strange word and the meaning is even stranger – it basically refers to when a living organism starts to eat itself.
However, this is an extremely important process for a plant to go through. When cytoplasm has unwanted material, it will enclose it within a vesicle that is called an autophagosome. This cell is then taken to the vacuole where it is broken down.
The autophagosome allows the vesicle to wrap around the unwanted cytoplasmic material with a double membrane, where it can be transported to the vacuole to be destroyed.
A similar process happens when the plant wants to recycle old material. This is important for the plant’s regeneration.
This is when the plant is broken down into the most basic components such as proteins, where they can be used by the cell once again. When you break down a protein, it can be reconstituted as a peptide, which can then be processed through the Golgi system.
There are many stressors and external processes outside the body that can kickstart this process of autophagy. For example, if a plant or animal organism is starving, then autophagy will break down fat cells to produce energy that the body can harness.
This is why you lose weight when you fast for consecutive days.
Previous studies suggested that the process of autophagy does not discriminate between the cells, however, it has now been discovered that it can target certain parts of the cell in response to specific conditions.
But vacuoles play many roles in various processes within the plant. For example, they are a very crucial component in cell death as well as the defense of certain cells.
Vacuoles, Cell Defense, And Cell Death
When a cell is in need of extra protection, then the vacuole undergoes certain processes in order to defend that cell.
The vacuole will start releasing enzymes such as hydrolytic enzymes and anti microbes that will help to get rid of an invading disease or pathogen. This function has not been fully understood yet, but it does play a very crucial role in immunizing the cell.
This very same mechanism has also been seen to operate in the case of cell death.
This is when an enzyme in the plant causes the vacuole to collapse completely, which then releases even more enzymes and anti microbes which not only help to destroy the pathogen but will also destroy the cell itself.
The vacuole is destroyed when the membrane is disrupted.
There is also another process through which cell death is triggered. This is when the central vacuole is fused with the plasma membrane to jettison antibacterial protease and other vacuole materials that will result in the death of a cell.
However, in addition to these more destructive properties, a vacuole can also help to preserve certain essential nutrients so they can be used at a later date.
Vacuoles That Store Protein
In tissues, there are certain designated places where protein gets stored so it can be used at a later date when necessary.
In a plant, for example, the seeds are where a lot of reserve protein is stored.
What happens in the preservation process is that the proteins need to be synthesized through a thing called a rough endoplasmic reticulum. These are connected flattened discs that are part of an organelle whose main function is to synthesize proteins.
Once these proteins have been fully synthesized, then they can be transported to the protein storage vacuole.
In order for these proteins to be taken from the Golgi complex and transported to the vacuole, it needs to be specifically targeted by a peptide. This will then allow the correct protein to be moved to the protein and stored.
The amount of PSVs that a plant has will differ depending on the genus. Some plants will have dense clusters of protein storage vacuoles. However, there might be multiple types of proteins stored in these cells, although this also depends on the plant.
What Are Gas Vacuoles?
These have a slightly different composition than other vacuoles, in that they are made up of cylindrical vesicles that allow air to be transported through them.
These types of vacuoles are found in bacteria and they have a permeable membrane that allows lighter material to pass through them. The membrane also causes the vesicles to be bonded together.
These also serve the function of allowing the bacteria to float or descend as they like by allowing them to inflate with air. This also permits bacteria to maintain their depth in the fluid that they are transported in.
What Are Contractile Vacuoles?
This is another type of organelle that can be found in algae, amoebas and ciliates. This kind of vacuole, as you might have guessed from the name, helps with regulating the osmotic pressure in the cell.
Osmotic pressure is the pressure that is applied to a soluble substance to allow it to pass through one medium into another. The level of pressure that is applied is also called osmoregulation.
The contracting vacuole complex has been suggested to occur in two different sections of the cell which are connected with two separate membranes. However, the studies of this mechanism are far from comprehensive.
These two membranes are very important for allowing osmoregulation to take place. This first of these membranes are made up of different vesicles, enzymes and tubules which are meant to produce protons.
This first membrane is fused completely to the second, which comes with a separate compartment.
In this second compartment, liquid is stored and fused to the membrane of each cell. This is when the cell is pumped at intervals which allows the vacuole to get rid of fluid.
This whole process stops the cell from accumulating too much water, which can lead to its swelling and even rupturing. This is why contractile vacuoles are very important for the purpose of regulating the amount of fluid that goes in and out of the vacuole.
What Are Sap Vacuoles?
You might have already heard of this kind of material. The sap is the main lifeblood of a tree and it comes filled with water, sugars, minerals and amino acids. This is a vacuole that is usually found at the center of a cell.
These organelles occupy most of the volume of a cell. As the plant grows and develops, the Golgi cluster produces provacuoles that then fuse to these sap vacuoles.
What Else Are Vacuoles Responsible For?
Vacuoles are also responsible for the cells growing in the first place. They help to maintain the rigidity of the cell, inflating in size until the cell itself grows completely. The more turgid these cells are, then the denser and more rigid the tissue.
The vacuoles are also responsible for the storage of not just proteins, but also things like metabolites, organic acids and sugars.
Vacuoles are also where the pigment of the plant is deposited. This is what gives different vegetables that red, blue and green hue.
What Does A Vacuole Look Like Under A Microscope?
If you are wanting to study the exact makeup of a vacuole, then we would recommend using only a light microscope. This way you can study the structure and movement of the vacuole itself.
You can use a few different colors to get this vacuole looking good again: neutral red, cresyl blue, methylene blue and pyronin.
How Can You Dye A Cell?
You’ll need a few ingredients before you dye your cell:
- A segment of plant – this can be the root or the leaves.
- Neutral red staining
- Distilled water
- Light microscope
- Glass slides
- Cover slips
Take a part of the plant, making sure that the segment is thin enough to fit under the microscope.
Once you have done this, then apply some of the red staining to the surface of your plant. You’ll need to stain the plant 0.01%.
Once you have done this, rinse the segment so that the excess dye runs off.
Then mount this on a glass slip and place it under the microscope for observation.
The stain should only stain the vacuoles rather than the other organelles of the plant. Looking under the microscope, you should notice the vacuoles will appear a deep red in color.
We hope that our study of vacuoles has given you a better understanding of how these cell structures operate and what they do in the plant.
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