Plasmodesmata- Definition, Structure, Functions and Diagram
Plants are multicellular organisms that need to coordinate their activities and share resources among their cells. However, plant cells are surrounded by rigid cell walls that prevent direct contact and communication between them. How do plant cells overcome this barrier and maintain their unity and function? The answer is plasmodesmata.
Plasmodesmata are microscopic channels that connect the cytoplasm of adjacent plant cells. They are formed from the plasma membrane and the endoplasmic reticulum of the parent cells during cell division or later in development. They allow the transport of molecules and macromolecules, such as water, ions, sugars, hormones, proteins, RNA, and even viruses, between cells. They are involved in cell-cell communication, development, and cell wall deposition.
Plasmodesmata are essential for plant life because they enable the integration and coordination of cellular activities across tissues and organs. For example, plasmodesmata mediate the transport of signals and nutrients between the source and sink tissues in phloem. They also regulate the movement of transcription factors and developmental regulators that control gene expression and cell differentiation. Moreover, plasmodesmata modulate the deposition and remodeling of the cell wall, which affects the mechanical properties and shape of plant cells.
Plasmodesmata are microscopic channels that connect the cytoplasm of adjacent plant cells. They are composed of three main layers: the plasma membrane, the cytoplasmic sleeve, and the desmotubule.
- The plasma membrane is a continuous extension of the cell membrane that surrounds each plasmodesma. It has a phospholipid bilayer structure that regulates the passage of molecules across the channel. The plasma membrane also maintains the electrical potential and pH balance between the connected cells.
- The cytoplasmic sleeve is a narrow space between the plasma membrane and the desmotubule that contains cytosol and various solutes. It is the main pathway for the transport of small molecules (such as sugars, amino acids, ions, and hormones) and macromolecules (such as proteins, RNA, and DNA) between cells. The cytoplasmic sleeve can be constricted or dilated by specialized proteins called plasmodesmata-associated proteins (PAPs) that respond to environmental signals or cellular needs.
- The desmotubule is a central tube that runs through the core of each plasmodesma. It is derived from the endoplasmic reticulum (ER) of the parent cell during cell division and remains continuous with the ER membranes of the connected cells. The desmotubule provides structural support for the plasmodesma and may also facilitate the transport of some ER-derived molecules (such as lipids and calcium) between cells.
The structure of plasmodesmata can vary depending on the type, location, and function of the cells they connect. For example, some plasmodesmata have additional components such as neck regions, branched structures, or sphincters that modulate their permeability and selectivity. Plasmodesmata can also form in different ways, such as primary plasmodesmata that are formed during cell division or secondary plasmodesmata that are inserted into existing cell walls between non-dividing cells. Plasmodesmata can also be classified into simple or complex types based on their number and arrangement in the cell wall. Simple plasmodesmata are single channels that connect two cells, while complex plasmodesmata are clusters of multiple channels that connect more than two cells.
Plasmodesmata are narrow channels that act as intercellular cytoplasmic bridges to facilitate communication and transport of materials between plant cells. They serve to connect the symplastic space in the plant and are extremely specialized channels that allow for intercellular movement of water, various nutrients, and other molecules.
Plasmodesmata function in intercellular communication, i.e., they allow molecules to pass directly from cell to cell. They can transport molecules with different sizes and charges, depending on the type and structure of the plasmodesmata. Some plasmodesmata are simple, with a single desmotubule and a narrow cytoplasmic sleeve. These plasmodesmata can only transport small molecules, such as ions, sugars, amino acids, and hormones. Other plasmodesmata are branched, with multiple desmotubules and a wider cytoplasmic sleeve. These plasmodesmata can transport larger molecules, such as proteins, RNA, and DNA.
Plasmodesmata have been shown to transport proteins (including transcription factors), short interfering RNA, messenger RNA, viroids, and viral genomes from cell to cell. These molecules can have various roles in regulating gene expression, cell differentiation, development, defense, and signaling in plants. For example, plasmodesmata can transport transcription factors that activate or repress specific genes in neighboring cells. They can also transport RNA molecules that silence or enhance gene expression by interfering with mRNA translation or stability. Plasmodesmata can also transport viroids and viral genomes that infect plant cells and cause diseases.
Plasmodesmata are also used by cells in the phloem, the vascular tissue that transports organic substances throughout the plant. The phloem consists of sieve-tube elements (STE), which are specialized cells that lack nuclei and most organelles, and companion cells (CC), which are adjacent cells that provide metabolic support and regulation to the STE. Plasmodesmata connect the CC with the STE and allow the symplastic transport of sugars, amino acids, hormones, and signaling molecules between them. Plasmodesmata also connect the CC with other neighboring cells, such as parenchyma cells and phloem fibers, and mediate the exchange of nutrients and information between them.
Plasmodesmata are dynamic structures that can change their size, shape, number, and permeability in response to various stimuli. For example, plasmodesmata can close or open depending on the environmental conditions, such as light intensity, temperature, pH, or osmotic pressure. Plasmodesmata can also be modified by proteins that bind to their components or by enzymes that alter their structure. These modifications can affect the transport capacity and selectivity of plasmodesmata. For instance, some proteins can increase or decrease the diameter of the cytoplasmic sleeve or the desmotubule. Some enzymes can degrade or synthesize callose, a polysaccharide that accumulates around the neck region of plasmodesmata and regulates their aperture.
Plasmodesmata are essential for plant growth, development, and survival. They enable the coordination and integration of cellular activities across different tissues and organs. They also allow the transmission of signals and molecules that help plants cope with biotic and abiotic stresses. Plasmodesmata are therefore key players in plant physiology and pathology.
In this blog post, we have learned about plasmodesmata, the fine cytoplasmic channels that connect the living cells of higher plants. We have seen how plasmodesmata are formed, structured, and function in intercellular communication and transport. We have also discussed some examples of molecules that can pass through plasmodesmata, such as proteins, RNA, and viral genomes.
Plasmodesmata are essential for the coordination and integration of plant tissues and organs. They allow the exchange of signals and substances that regulate growth, development, defense, and adaptation. They also enable the symplastic transport of photosynthates and other metabolites in the phloem. Plasmodesmata are dynamic structures that can change their size, number, and permeability in response to various stimuli and conditions.
Plasmodesmata are fascinating and complex structures that reveal the remarkable diversity and sophistication of plant life. They are also important targets for biotechnology and crop improvement, as they can modulate the resistance or susceptibility of plants to various pathogens and stresses. By understanding the structure and function of plasmodesmata, we can gain more insights into the biology and ecology of plants.🌱
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