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Key Highlights
- Plasmodesmata are microscopic cytoplasmic canals that allow the transportation of molecules and substances between adjacent cells.
- It is used to regulate the passage of molecules between the plant cells.
- There are two types of plasmodesmata: primary plasmodesmata and secondary plasmodesmata.
- This cytoplasmic channel helps in molecular translocation and cellular communication.
- Some common examples of plasmodesmata include charophyceae, charales, phaeophyceae and coleochaetales.
Plasmodesmata are microscopic channels that allow molecules and substances to pass through the cell walls of plants and algal cells. These channels are analogous to gap junctions in animal cells.
- It was discovered by Eduard Tangle in the 1879 and Strasburger in the 1901, respectively.
- The origin of plasmodesmata is initiated in the endoplasmic reticulum.
- It acts as a bridge that connects the cytoplasm of two cells together.
Key Terms: Plasmodesmata, Cytoplasm, Endoplasmic Reticulm, Primary Plasmodesmata, Secondary Plasmodesmata, Plasmodesmata Functions, Plasmodesmata Structure, Cell Wall, Cells
What is Plasmodesmata?
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Plasmodesmata are small intercellular organelles that allow the movement of nutrients and various molecules between cell walls in the plant and algal cells.
- It links the plant cells to syncytial tissues to overcome the barrier of the plasma membrane.
- Plasmodesmata is divided into categories, namely primary plasmodesmata and secondary plasmodesmata.
- Primary plasmodesmata are formed during cell division.
- On the other hand, secondary plasmodesmata are formed when plants' cells mature.
- They consist of desmotubule and cytoplasmic sleeves and help in short-distance movements.
- It undergoes cell division when endoplasmic reticulum get trapped in the new cell wall that is produced to create daughter cells.
- Each plant cell consists of 103 -105 plasmodesmata.
- They are also called "bridges" between two plant cells as they act like channels which allow communication with other cells in a tissue.
- Some common examples of plasmodesmata include embryophytes, charales, phaeophyceae and coleochaetales.
Plasmodesmata
Plasmodesmata Structure
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Plasmodesmata are like tubes linking one cell to another. They are roughly cylindrical, membrane-lined channels with a diameter of 20 to 40 mm.
- The plasmodesmata consists of three main layers: the plasma membrane, the cytoplasmic sleeve, and the desmotubule.
- Between the endoplasmic reticulum, there is the cytoplasmic sleeve, where the transfer of molecules occurs.
- Diffusion allows smaller ions and molecules, such as sugar and amino acids, to move through the plasmodesmata with ease.
- The cytoplasmic sleeve contains various structures, such as actin and myosin, which provide contractile forces for transportation.
- The annulus of the cytosol is found between the outside of the desmotubule and the inner face of the cylindrical plasma membrane.
- It often appears to be constricted at each end of the plasmodesmata.
- These constrictions can regulate the flux of molecules through the annulus that joins the two cytosols.
- In plasmodesmata, the plasma membrane portion is a continuous cell membrane extension.
- It has a similar phospholipid bilayer structure with a hydrophobic and hydrophilic exterior.
Plasmodesmata Functions
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Some important functions of plasmodesmata are as follows:
- It plays an important role in both communication and molecule translocation.
- Plasmodesmata helps facilitate the movement of molecules ranging from small photosynthetic products.
- It includes the transportation of water from roots to large proteins, mRNA, short interfering RNA, and viroids from cell to cell.
- Earlier plasmodesmata were known for passive pores used in the movement of nutrients.
- Actin structures present in the cytoplasmic sleeve were found to help in the movement of transcription factors.
- The sugar responsible for the opening and closure of plasmodesmal pores is callose.
- Another function of plasmodesmata is in the symplastic system for the movement of water through the cells.
- In response to any intruder, such as plant viruses, the callose is deposited in the wall of the plasmodesmal pore, and the pore closes.
Sample Questions
Ques: What are plasmodesmata? Explain? (2 marks)
Ans: One of the fundamental differences between an animal cell and a plant cell is the presence of a cell wall which is a rigid and tough structure which develops a problem for the plant in the movement of molecules that is why Plasmodesmata is required. It is a channel through the plant cells that allows the passage of molecules and substances in back and forth motion.
Ques: Explain the structure and function of plasmodesmata? (2 marks)
Ans: Plasmodesmata is a tube-like channel of 20-40mm of diameter that allows the movement of molecules through cells.The Plasmodesmata are made up of three main layers that are , the plasma membrane,the cytoplasmic sleeve,and the desmotubule.
- Plasmodesmata plays an important role in both communication and in molecule translocation, but the problem with plant cells is that it has a tough,rigid cell wall.
- It is difficult for larger molecules to penetrate the cell wall that is why plasmodesmata are necessary.
Ques: What is callose? How does it help the plasmodesmal pores from intruders? (2 marks)
Ans: Researchers believe that the sugar responsible for the opening and closure plasmodesmal pores is callose. In response to any intruder such as plant viruses the callose gets deposited in the wall of the plasmodesmal pore and the pore closes.
Ques: What is the size of plasmodesmata in normal conditions? (2 marks)
Ans: Plasmodesmata is a tube-like channel that allows the transport of nutrients from one cell to another. The size of a plasmodesmata can be 20-40mm.
Ques: What is desmotubule? (2 marks)
Ans: Desmotubules are endomembrane derived structures of the plasmodesmata that connect the endoplasmic reticulum of two adjacent plant cells. The exact role of the desmotubule remains unclear, and research is ongoing to determine its precise role in intercellular communication within plants.
Ques: What are the different molecules plasmodesmata help to facilitate from one cell to another? (2 marks)
Ans: Plasmodesmata helps in facilitating the movement of molecules ranging from small photosynthetic products like water from roots to large proteins and mRNA, short interfering RNA, viroids, from cell to cell.
Ques: What is a symplastic system? (2 marks)
Ans: The symplastic system is the system of interconnected protoplasts. Neighbouring cells are connected through cytoplasmic strands that extend through plasmodesmata. The function of plasmodesmata is in the symplastic system for the movement of water through the cells.
Ques: Why is plasmodesmata necessary for plants? (2 marks)
Ans: Plant cells are different from animal cells from the fact that plant cells have cell walls. These cell walls are a tough and rigid structure therefore creating problems for larger molecules to penetrate through the cells. Hence, plasmodesmata is necessary for the movement of molecules through cell to cell for the survival of plant cells.
Ques: What is the difference between plasmodesmata and middle lamella? (3 marks)
Ans: The difference between plasmodesmata and middle lamella are as follows:
| Plasmodesmata | Middle Lamella |
|---|---|
| Plasmodesmata are channels that connect the plant cells for communication and transportation. | Middle lamella is found between plant cells. |
| It consists of cytoplasmic strands. | It is composed of carbohydrates called pectin. |
| Plasmodesmata is formed during cell division. | Middle lamella is formed during maturation. |
Ques: What is desmosomes? (2 marks)
Ans: Desmosomes, also called macula adherens, are specialized structures found on the plasma membrane of cells. Their primary function is to create strong cell-to-cell adhesion, which acts like microscopic rivets or glue. This strong adhesion is crucial for tissues that experience mechanical stress or need to form a barrier.
Ques: What is the difference between plasmodesmata and gap junctions? (3 marks)
Ans: The difference between plasmodesmata and gap junctions are as follows:
| Plasmodesmata | Gap Junctions |
|---|---|
| Plasmodesmata is found in plants and algal cells. | Gap Junctions are found in animal cells. |
| Its structure include cell wall. | Its structure include plasma membrane. |
| Plasmodesmata provides water, nutrients, ions, small molecules and some RNA. | Gap Junctions provide small molecules and electrical signals. |
Ques: What is the role of plasmodesmata? (2 marks)
Ans: Plasmodesmata play a vital role in plants and algal by facilitating communication and exchange of molecules between plant cells. It allows water, essential nutrients (sugars, amino acids, minerals), and dissolved solutes to pass between cells. This enables the movement of resources throughout the plant, ensuring proper nourishment for different tissues.
Ques: What are the negative effects of plasmodesmata? (2 marks)
Ans: The most common side effect of plasmodesmata is the spread of viruses. Viruses are responsible for breaking down filaments within the plasmodesmata so they can move easily with the plant cells. For example, when the cucumber mosaic virus gets into plants, it can easily pass through almost every cell by utilising viral movement proteins to transport themselves through the plasmodesmata.
Ques: Is plasmodesmata living or nonliving? (2 marks)
Ans: Plasmodesmata are considered living, which are formed by extensions of the endoplasmic reticulum within plant cells. The endoplasmic reticulum helps in the synthesis of protein, lipids, and other cellular processes. They help transport substances and molecules through the cytoplasm.
Ques: How are plasmodesmata formed? (2 marks)
Ans: Plasmodesmata are formed during cell division when different parts of the parent cell's endoplasmic reticulum get trapped inside the cell wall, resulting in the production of daughter cells. Thousands of plasmodesmata are formed to connect the daughter cells. Once the cell walls are established, the plasma membranes of the daughter cells will fuse at the opening of the plasmodesmata.
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