---
title: "Plasmodesmata: Structure, Function, Formation and Transport"
description: "Get Free Biology Notes"
url: https://biologynotesonline.com/plasmodesmata/
---

# Plasmodesmata: Structure, Function, Formation and Transport

Plasmodesmata are channels connecting plant cells. Learn their structure, function, formation, transport, regulation, distribution, and key comparisons.

**Plasmodesmata are microscopic, plasma membrane-lined channels that pass through the cell wall between adjacent plant cells and allow direct intercellular communication and cell-to-cell transport.** 

The term **plasmodesmata** is plural, while a single channel is called a **plasmodesma**. Plant cells have a rigid cell wall which keeps the neighbouring cells physically separated. 

Plasmodesmata cross this wall and form a direct connection between these cells, they are not simply holes present in the cell wall. The plasma membrane is continued through the channel between one cell and the adjacent cell. 

Their major function is the controlled movement of materials and cellular signals from one plant cell to another. Movement through this connected cytoplasmic pathway is referred to as **symplastic transport**.

## Distribution of Plasmodesmata

- Plasmodesmata are mainly present between the living cells of plants. Most plant cells remain connected with the neighbouring cells through these channels. This forms the continuous symplastic connection in different plant tissues.

- They are found in leaves, stems, roots and growing tissues of the plant. The number of plasmodesmata is not same everywhere. It changes with the cell type, tissue and stage of development.

- Plasmodesmata are not present as functional connections between every plant cell. Some cells become symplastically isolated during differentiation. Mature guard cells, for example, generally lose their plasmodesmatal connection with the surrounding epidermal cells.

- In the xylem, plasmodesmata are found between the living [xylem parenchyma cells](https://biologynotesonline.com/xylem-parenchyma-definition-structure-types-functions/). These cells remain connected with other living cells and materials can move through the symplastic pathway.

- Mature vessel elements and tracheids are dead cells. Functional plasmodesmata are not present between these dead conducting elements and the neighbouring living xylem cells. The connection between vessel or tracheid and xylem parenchyma occurs through pits, not through functional plasmodesmata.

- Plasmodesmata are also present in some groups of algae. Similar plasmodesmata occur in some streptophyte algae. Plasmodesmata or plasmodesmata-like connections have also developed in some other algal groups, including brown algae, but their structure and evolutionary origin are not always same as those of land plants.

## Types of Plasmodesmata

**Plasmodesmata (PD)** are mainly divided into primary and secondary types based on the time and mode of their formation. Different structural forms of PD are also present.

![Classification of plasmodesmata by developmental origin into primary and secondary types and by morphology into simple, twinned, and branched forms.](https://biologynotesonline.com/wp-content/uploads/2024/10/Types-and-Classification-of-Plasmodesmata-1024x725.webp)Classification of plasmodesmata by developmental origin into primary and secondary types and by morphology into simple, twinned, and branched forms.

- **Primary plasmodesmata-** These PD are formed during cytokinesis when strands of the **endoplasmic reticulum (ER)** become trapped within the developing cell plate. They establish connections between newly formed daughter cells. Primary PD are generally formed initially as simple channels, and their structure may change later during cell development.

- **Secondary plasmodesmata-** Secondary PD are formed after cytokinesis in an already existing cell wall. They may arise completely de novo or by modification and doubling of pre-existing PD. Unlike primary PD, secondary PD can develop between cells that were not produced by the same cell division.

Based on their structure, PD can also occur in the following forms-

- **Simple plasmodesmata-** It consists of a single, unbranched channel passing through the cell wall. Simple PD are commonly present in young and immature plant tissues.

- **Twinned plasmodesmata-** Two simple PD occur very close to one another and are referred to as twinned PD. These can be formed during modification or doubling of an existing channel.

- **Branched or complex plasmodesmata-** These contain multiple interconnected channels instead of one simple channel. A wider central cavity may also occur between the branches. Branched PD become more common as many plant tissues mature, although they can also be present in immature tissues.

## Structure of Plasmodesmata

The main structural parts of **plasmodesmata (PD)** are as follows-

![Longitudinal cutaway of a mature plasmodesma showing the plasma membrane-lined pore, central desmotubule, cytoplasmic sleeve, neck regions, callose, and continuous ER.](https://biologynotesonline.com/wp-content/uploads/2024/10/Structure-of-Plasmodesmata-1024x512.webp)Longitudinal cutaway of a mature plasmodesma showing the plasma membrane-lined pore, central desmotubule, cytoplasmic sleeve, neck regions, callose, and continuous ER.

- **[Plasma membrane (PM)](https://biologynotesonline.com/cell-membrane-plasma-membrane-structures-and-functions/)–** The PD is lined by the PM, which is continuous with the PM of the two neighbouring plant cells. It forms the outer membrane of the channel while crossing the cell wall.

- **Desmotubule-** A narrow strand of the **[endoplasmic reticulum (ER)](https://biologynotesonline.com/endoplasmic-reticulum/)** is present at the centre of most PD. This is called the desmotubule. It is continuous with the ER of adjacent cells and remains tightly compressed inside the channel.

- **Cytoplasmic sleeve-** The space between the desmotubule and the PM is known as the cytoplasmic sleeve. It contains cytosol. The cytoplasmic sleeve provides the major route through which molecules pass from one neighbouring cell to another.

- **Spoke-like tethers-** The desmotubule and PM are connected at different places by spoke-like or tethering structures. These can divide the cytoplasmic sleeve into several very narrow channels, while their complete molecular composition is still not clearly known.

- **Neck region and central cavity-** At both ends of many PD, the space between the PM and desmotubule becomes narrow. These are referred to as the “neck regions”. The middle region can be wider and forms a central cavity.

- **Plasmodesmal cell wall-** PD are surrounded by a specialized region of the [cell wall](https://biologynotesonline.com/cell-wall-structure-composition-functions/). **Callose**, a β-1,3-glucan, is commonly deposited around the neck region and its accumulation can narrow the channel opening.

- **Size and form-** The outer diameter of PD is generally in the nanometre range and often about 25-50 nm, but it differs with tissue and plant species. They may occur as a simple single channel or develop into more complex branched forms.

## Formation of Plasmodesmata

**Plasmodesmata (PD)** can be formed during cell division as primary PD or later in an already formed cell wall as secondary PD. The formation of primary PD is closely associated with formation of the cell plate during [cytokinesis](https://biologynotesonline.com/cytokinesis/).

![Comparison of primary plasmodesmata formation during cytokinesis with twinning and proposed de novo formation of secondary plasmodesmata in an existing cell wall.](https://biologynotesonline.com/wp-content/uploads/2024/10/Formation-of-Primary-and-Secondary-Plasmodesmata-1024x725.webp)Comparison of primary plasmodesmata formation during cytokinesis with twinning and proposed de novo formation of secondary plasmodesmata in an existing cell wall.

### Formation of Primary Plasmodesmata

The formation takes place in the following steps-

- **Formation of cell plate-** During cytokinesis, Golgi-derived vesicles are transported to the middle region of the dividing plant cell. These vesicles fuse within the phragmoplast and start forming the new cell plate between two daughter cells.

- **Entrapment of endoplasmic reticulum-** Strands of the **endoplasmic reticulum (ER)** extend through the region where the cell plate is being formed. Some of these ER strands remain trapped between the fusing cell plate membranes instead of being removed.

- **Formation of the plasmodesmal pore-** The cell plate continues to grow around these ER strands. The membrane of the developing cell plate surrounds the trapped ER and later becomes continuous with the **plasma membrane (PM)** of both daughter cells. A narrow pore is maintained at these places.

- **Desmotubule formation-** The trapped ER strand becomes highly constricted inside the developing pore and forms the central **desmotubule**. Reticulon proteins are thought to take part in this narrowing and shaping of the ER membrane.

- **Formation of cytoplasmic sleeve-** A narrow space remains between the desmotubule and the surrounding PM. This space forms the cytoplasmic sleeve, which directly connects the cytoplasm of the two neighbouring cells.

- **Maturation of the cell plate-** The cell plate gradually develops into the new cell wall. The regions occupied by the ER-derived pores remain open as primary PD, while cell wall material is deposited around them.

### Formation of Secondary Plasmodesmata

Secondary PD are formed after cytokinesis in a pre-existing cell wall. Their exact molecular process is still not completely known. Two main ways have been described.

- **Twinning-** A new PD develops very close to an already existing plasmodesma. During this process, simple PD may pass through Y-, X-, or H-shaped intermediate forms and produce neighbouring plasmodesmal channels.

- **De novo formation-** In this type, a new channel is formed without a pre-existing PD at that position. The cell wall becomes locally thin, and the PM and ER are brought close to the wall region.

The PM and ER can then extend into the thinned wall region and eventually establish a connection with the neighbouring cell. The cellular machinery responsible for membrane penetration and final fusion is not yet clearly understood.

## What Passes Through Plasmodesmata

Different small and large molecules can pass through **plasmodesmata (PD)**. Small solutes usually move more freely, while movement of larger molecules is more controlled.

- **Water and ions-** Water and different inorganic ions can move from one plant cell to another through PD. These small substances pass through the cytoplasmic pathway comparatively easily.

- **Sugars, amino acids and metabolites-** Small sugars, amino acids and many other metabolites are transported through PD. Their movement is generally passive and depends on molecule size and the concentration difference between adjacent cells.

- **Plant hormones and signalling molecules-** Different small hormones and cellular signals can also pass through PD during communication between neighbouring cells.

- **Proteins-** Certain proteins are transported from one cell to another. These include regulatory proteins such as transcription factors. Larger proteins do not simply diffuse like small solutes, their movement can involve specific interaction with PD and changes in the opening of the channel.

- **Ribonucleic acid (RNA)-** Different RNA molecules can move through PD. Messenger RNA (mRNA), small RNA molecules and RNA-protein complexes have been shown to undergo cell-to-cell transport through these channels.

- **Viral components-** Plant viruses also use PD for spreading into the neighbouring cells. Viral nucleic acids and protein-nucleic acid complexes can pass through the channel, and viral movement proteins may increase the normal transport capacity of PD.

- **Passage depends on plasmodesmal permeability-** PD are not permanently open for all molecules. The maximum size that can pass through a particular channel is commonly described as the **size exclusion limit (SEL)**. Size, shape and charge of the molecule can affect movement, while the permeability of PD also changes with tissue, developmental stage and regulation of the channel.

## Regulation of Plasmodesmatal Transport

The transport through **plasmodesmata (PD)** does not remain same in all conditions. The PD opening can become narrow or more open, controlling movement of materials between the neighbouring cells.

![Plasmodesmata in permissive and restricted states showing movement of small solutes, proteins, and RNA and narrowing of the channel as callose accumulates at the neck.](https://biologynotesonline.com/wp-content/uploads/2024/10/Plasmodesmatal-Transport-and-Callose-Regulation-1024x576.png)Plasmodesmata in permissive and restricted states showing movement of small solutes, proteins, and RNA and narrowing of the channel as callose accumulates at the neck.

- **Callose deposition-** Callose is deposited around the neck region of PD. More callose makes the opening narrow. Less materials can pass through it and the **size exclusion limit (SEL)** decreases.

- **Callose removal-** The deposited callose can also be broken down. This opens up the channel and increases movement through PD. Callose synthases take part in callose formation, while β-1,3-glucanases break down the callose.

- **Calcium and reactive oxygen species (ROS)-** Ca²⁺ and ROS also take part in regulation of PD. Under some stress conditions, increased ROS is associated with more callose deposition. Changes in Ca²⁺ signalling can alter the permeability of the channel.

- **Plasmodesmata-associated proteins-** Different proteins are present in and around PD, some are involved in regulating callose and membrane organization. Other proteins take part in controlling movement of particular molecules through PD.

- **Developmental changes-** During plant growth, the number and permeability of PD can change. Some cells remain highly connected. In other differentiated tissues the symplastic movement becomes restricted.

- **Hormones and environmental conditions-** Plant hormones, light and cold can change plasmodesmatal transport. These conditions can act through callose regulation and other PD-associated signalling pathways.

- **Pathogen and stress response-** During pathogen attack, callose may accumulate around the PD. The channel becomes narrow and cell-to-cell movement is reduced. Plant viruses can also change the normal PD transport and use the channel for movement from infected cell to the neighbouring cell.

## Functions of Plasmodesmata

Some of the important functions of **plasmodesmata (PD)** are as follows-

- **Cell-to-cell transport-** PD form a direct cytoplasmic connection between the neighbouring plant cells. Ions, small metabolites and other cellular substances can move through these channels. This movement forms the symplastic route.

- **Intercellular signalling-** Different cellular signals are passed from one cell to another through PD. Plant hormones and other mobile signalling molecules can also use this pathway for communication between neighbouring cells.

- **Movement of proteins and ribonucleic acid (RNA)-** PD are also used for transport of certain larger molecules. Specific proteins, small RNA and ribonucleoprotein complexes can pass through these channels. Some of these molecules take part in developmental signalling.

- **Plant growth and development-** During plant development, regulatory molecules move through PD and help in cell differentiation and developmental pattern formation. The transport through these channels is controlled between particular cells and tissues.

- **Transport of nutrients-** Sugars, metabolites and other materials are transported through the connected symplastic pathway. PD also take part in loading and unloading of materials associated with the [phloem transport system](https://biologynotesonline.com/translocation-in-phloem-structure-phloem-loading-and-unloading/).

- **Response to stress and environmental signals-** The permeability of PD does not remain fixed. It can increase or decrease according to developmental condition and different external stresses, controlling the movement of materials between the adjacent cells.

- **Movement of plant viruses-** Many plant viruses use PD to move from an infected cell into the neighbouring cells. Viral movement proteins can alter the normal transport property of PD, allowing viral components to pass through the channel.

## Plasmodesmata At a Glance

**Feature****Quick exam point****Definition**Plasmodesmata are microscopic, plasma membrane-lined channels passing through the cell wall between neighbouring plant cells.**Singular form****Plasmodesma****Plural form****Plasmodesmata****Main role**Direct cell-to-cell transport and intercellular communication.**Occurrence**Mainly present between living plant cells. They are also found in some groups of algae.**In xylem**Present between living xylem cells such as xylem parenchyma. Mature vessel elements and tracheids are dead and do not have functional plasmodesmata.**Main structural parts**Plasma membrane, cytoplasmic sleeve and central desmotubule.**Desmotubule**A narrow strand derived from the **endoplasmic reticulum (ER)** and running through the centre of the channel.**Cytoplasmic sleeve**Space between the desmotubule and plasma membrane. Much of the cell-to-cell movement takes place through this region.**Primary plasmodesmata**Formed during cytokinesis while the new cell plate is being formed.**Secondary plasmodesmata**Formed later in an already existing cell wall.**Structural forms**Simple, twinned and branched or complex plasmodesmata.**Materials transported**Water, ions, sugars, amino acids, metabolites, hormones and other small cellular molecules.**Large molecules**Certain proteins and different forms of **ribonucleic acid (RNA)** can also move through plasmodesmata. Their movement is regulated.**Viral movement**Many plant viruses use plasmodesmata for movement from infected cell to neighbouring cells.**Symplastic transport**Movement of materials through the connected cytoplasm of neighbouring cells by plasmodesmata.**Callose**Deposited mainly around the neck region. More callose narrows the channel and reduces transport.**Callose removal**Breakdown of callose opens up the channel and increases plasmodesmatal transport.**Size exclusion limit (SEL)**It represents the size limit for passage through a particular plasmodesmatal channel.**Transport regulation**Controlled by callose, Ca²⁺, reactive oxygen species (ROS), PD-associated proteins, developmental condition and environmental signals.**Are all plant cells connected?**No. Some cells become symplastically isolated during differentiation.

## References

- Benitez-Alfonso, Y. (2014). Symplastic intercellular transport from a developmental perspective. *Journal of Experimental Botany, 65*(7), 1857–1863. [https://doi.org/10.1093/jxb/eru067](https://doi.org/10.1093/jxb/eru067)

- Brunkard, J. O. (2024). Communicating across cell walls: Structure, evolution, and regulation of plasmodesmatal transport in plants. In M. Kloc, J. Z. Kubiak, & M. Halasa (Eds.), *Intercellular and interorganellar transfer and communication in biology and medicine* (pp. 73–86). Springer. [https://doi.org/10.1007/978-3-031-62036-2_4](https://doi.org/10.1007/978-3-031-62036-2_4)

- Brunkard, J. O., & Burch-Smith, T. M. (2026). Plasmodesmata. *Journal of Experimental Botany, 77*(3), 689–691. [https://doi.org/10.1093/jxb/eraf518](https://doi.org/10.1093/jxb/eraf518)

- Burch-Smith, T. M., Stonebloom, S., Xu, M., & Zambryski, P. C. (2011). Plasmodesmata during development: Re-examination of the importance of primary, secondary, and branched plasmodesmata structure versus function. *Protoplasma, 248*(1), 61–74. [https://doi.org/10.1007/s00709-010-0252-3](https://doi.org/10.1007/s00709-010-0252-3)

- Chen, J., Xu, X., Liu, W., Feng, Z., Chen, Q., Zhou, Y., Sun, M., Gan, L., Zhou, T., & Xuan, Y. (2024). Plasmodesmata function and callose deposition in plant disease defense. *Plants, 13*(16), 2242. [https://doi.org/10.3390/plants13162242](https://doi.org/10.3390/plants13162242)

- De Storme, N., & Geelen, D. (2014). Callose homeostasis at plasmodesmata: Molecular regulators and developmental relevance. *Frontiers in Plant Science, 5*, 138. [https://doi.org/10.3389/fpls.2014.00138](https://doi.org/10.3389/fpls.2014.00138)

- Ghoshroy, S., Lartey, R., Sheng, J., & Citovsky, V. (1997). Transport of proteins and nucleic acids through plasmodesmata. *Annual Review of Plant Physiology and Plant Molecular Biology, 48*, 27–50. [https://doi.org/10.1146/annurev.arplant.48.1.27](https://doi.org/10.1146/annurev.arplant.48.1.27)

- Haywood, V., Kragler, F., & Lucas, W. J. (2002). Plasmodesmata: Pathways for protein and ribonucleoprotein signaling. *The Plant Cell, 14*(Suppl.), S303–S325. [https://doi.org/10.1105/tpc.000778](https://doi.org/10.1105/tpc.000778)

- Knox, K., Wang, P., Kriechbaumer, V., Tilsner, J., Frigerio, L., Sparkes, I., Hawes, C., & Oparka, K. (2015). Putting the squeeze on plasmodesmata: A role for reticulons in primary plasmodesmata formation. *Plant Physiology, 168*(4), 1563–1572. [https://doi.org/10.1104/pp.15.00668](https://doi.org/10.1104/pp.15.00668)

- Kragler, F., Monzer, J., Xoconostle-Cázares, B., & Lucas, W. J. (2000). Peptide antagonists of the plasmodesmal macromolecular trafficking pathway. *The EMBO Journal, 19*(12), 2856–2868. [https://doi.org/10.1093/emboj/19.12.2856](https://doi.org/10.1093/emboj/19.12.2856)

- Li, Z. P., Paterlini, A., Glavier, M., & Bayer, E. M. (2021). Intercellular trafficking via plasmodesmata: Molecular layers of complexity. *Cellular and Molecular Life Sciences, 78*(3), 799–816. [https://doi.org/10.1007/s00018-020-03622-8](https://doi.org/10.1007/s00018-020-03622-8)

- Nicolas, W. J., Grison, M. S., & Bayer, E. M. (2018). Shaping intercellular channels of plasmodesmata: The structure-to-function missing link. *Journal of Experimental Botany, 69*(1), 91–103. [https://doi.org/10.1093/jxb/erx225](https://doi.org/10.1093/jxb/erx225)

- Patrick, J. W. (1997). Phloem unloading: Sieve element unloading and post-sieve element transport. *Annual Review of Plant Physiology and Plant Molecular Biology, 48*, 191–222. [https://doi.org/10.1146/annurev.arplant.48.1.191](https://doi.org/10.1146/annurev.arplant.48.1.191)

- Rutschow, H. L., Baskin, T. I., & Kramer, E. M. (2011). Regulation of solute flux through plasmodesmata in the root meristem. *Plant Physiology, 155*(4), 1817–1826. [https://doi.org/10.1104/pp.110.168187](https://doi.org/10.1104/pp.110.168187)

- Sager, R., & Lee, J.-Y. (2014). Plasmodesmata in integrated cell signalling: Insights from development and environmental signals and stresses. *Journal of Experimental Botany, 65*(22), 6337–6358. [https://doi.org/10.1093/jxb/eru365](https://doi.org/10.1093/jxb/eru365)

- Schreiber, J. M., Limpens, E., & de Keijzer, J. (2024). Distributing plant developmental regulatory proteins via plasmodesmata. *Plants, 13*(5), 684. [https://doi.org/10.3390/plants13050684](https://doi.org/10.3390/plants13050684)

- Słupianek, A., Dolzblasz, A., & Sokołowska, K. (2021). Xylem parenchyma—Role and relevance in wood functioning in trees. *Plants, 10*(6), 1247. [https://doi.org/10.3390/plants10061247](https://doi.org/10.3390/plants10061247)

- Stonebloom, S., Brunkard, J. O., Cheung, A. C., Jiang, K., Feldman, L., & Zambryski, P. (2012). Redox states of plastids and mitochondria differentially regulate intercellular transport via plasmodesmata. *Plant Physiology, 158*(1), 190–199. [https://doi.org/10.1104/pp.111.186130](https://doi.org/10.1104/pp.111.186130)

- Tilsner, J., Nicolas, W., Rosado, A., & Bayer, E. M. (2016). Staying tight: Plasmodesmal membrane contact sites and the control of cell-to-cell connectivity in plants. *Annual Review of Plant Biology, 67*, 337–364. [https://doi.org/10.1146/annurev-arplant-043015-111840](https://doi.org/10.1146/annurev-arplant-043015-111840)

- Tomkins, M., Hughes, A., & Morris, R. J. (2021). An update on passive transport in and out of plant cells. *Plant Physiology, 187*(4), 1973–1984. [https://doi.org/10.1093/plphys/kiab406](https://doi.org/10.1093/plphys/kiab406)

- Ueki, S., & Citovsky, V. (2011). To gate, or not to gate: Regulatory mechanisms for intercellular protein transport and virus movement in plants. *Molecular Plant, 4*(5), 782–793. [https://doi.org/10.1093/mp/ssr060](https://doi.org/10.1093/mp/ssr060)

- Ueki, S., & Citovsky, V. (2014). Plasmodesmata-associated proteins: Can we see the whole elephant? *Plant Signaling & Behavior, 9*(2), e27899. [https://doi.org/10.4161/psb.27899](https://doi.org/10.4161/psb.27899)

- Verma, D. P. S. (2001). Cytokinesis and building of the cell plate in plants. *Annual Review of Plant Physiology and Plant Molecular Biology, 52*, 751–784. [https://doi.org/10.1146/annurev.arplant.52.1.751](https://doi.org/10.1146/annurev.arplant.52.1.751)

- Wegner, L., Porth, M. L., & Ehlers, K. (2023). Multicellularity and the need for communication—A systematic overview on (algal) plasmodesmata and other types of symplasmic cell connections. *Plants, 12*(18), 3342. [https://doi.org/10.3390/plants12183342](https://doi.org/10.3390/plants12183342)

- Worthington, L.-A., & Lee, J.-Y. (2026). Plasmodesmal regulation: Context matters. *Journal of Experimental Botany, 77*(8), 2177–2196. [https://doi.org/10.1093/jxb/erag008](https://doi.org/10.1093/jxb/erag008)

- Yadav, S. R., Yan, D., Sevilem, I., & Helariutta, Y. (2014). Plasmodesmata-mediated intercellular signaling during plant growth and development. *Frontiers in Plant Science, 5*, 44. [https://doi.org/10.3389/fpls.2014.00044](https://doi.org/10.3389/fpls.2014.00044)

- Yang, D., Wei, K., Li, J., Peng, G., & Tyree, M. T. (2020). Inferring the role of pit membranes in solute transport from solute exclusion studies in living conifer stems. *Journal of Experimental Botany, 71*(9), 2828–2837. [https://doi.org/10.1093/jxb/eraa058](https://doi.org/10.1093/jxb/eraa058)

- Zambryski, P. (2004). Cell-to-cell transport of proteins and fluorescent tracers via plasmodesmata during plant development. *The Journal of Cell Biology, 164*(2), 165–168. [https://doi.org/10.1083/jcb.200310048](https://doi.org/10.1083/jcb.200310048)

- Zanini, A. A., & Burch-Smith, T. M. (2024). New insights into plasmodesmata: Complex “protoplasmic connecting threads.” *Journal of Experimental Botany, 75*(18), 5557–5567. [https://doi.org/10.1093/jxb/erae307](https://doi.org/10.1093/jxb/erae307)