Plasmodesma 2026-11-05
A plasmodesma, plural plasmodesmata, is a membrane-lined connection crossing a plant cell wall between neighboring cells. It provides a route for intercellular exchange, including movement of some signaling molecules and macromolecules. A plasmodesma contains a tubular strand of endoplasmic reticulum within its enclosing cell membrane; it is an organized cellular interface, rather than simply a hole in the wall.[ref]
Architecture and permeability of post-cytokinesis plasmodesmata lacking cytoplasmic sleeves by William J. Nicolas and others. Abstract: exchanged material, plasma membrane lining and internal ER strand
Transport changes during development. A cotton fibre study followed a fluorescent tracer from the seed coat into elongating fibres with confocal microscopy. Access through plasmodesmata was observed early, blocked around day 10 and observed again around day 16. Reverse tracer movement supplied a complementary test, distinguishing transport connectivity from the mere presence of a channel in a section.[ref]
The control of single-celled cotton fiber elongation by developmentally reversible gating of plasmodesmata and coordinated expression of sucrose and K+ transporters and expansin by Y. L. Ruan and others. Abstract; Figures1–2: tracer movement at different developmental stages and in opposite directions
The apparent width in an image is not the whole explanation of permeability. A 2017 electron tomography study found newly formed plasmodesmata with no visible open cytoplasmic sleeve, yet observed macromolecular diffusion. Architecture and transport must therefore be measured together.[ref]
Architecture and permeability of post-cytokinesis plasmodesmata lacking cytoplasmic sleeves by William J. Nicolas and others. Abstract: post-cytokinesis structure and macromolecular permeability
Plasmodesmal permeability 2026-11-05
Plasmodesmal permeability describes how readily specified material moves between plant cells through plasmodesmata under stated conditions. It depends on the transported substance and the state of the connections; a count of channels alone does not specify exchange. Passage through a plasmodesma is also a different route from crossing a lipid cell membrane.
The distinction is experimentally accessible. In developing cotton fibres, investigators used a fluorescent tracer and confocal microscopy to follow access between the seed coat and growing cells. Access was observed early, blocked around day 10 and observed again around day 16. Tests of movement in the reverse direction provided a complementary functional comparison.[ref]
The control of single-celled cotton fiber elongation by developmentally reversible gating of plasmodesmata and coordinated expression of sucrose and K+ transporters and expansin by Y. L. Ruan and others. Abstract; Figures1–2: developmental changes and reverse tracer movement
An original toy model illustrates why channel number is insufficient. Ten connections each carrying two tracer units per unit time give 20 units per unit time altogether. Twenty connections each carrying half a unit give 10. These invented values compare total transfer in an equal-channel model; they are not a universal transport law.
Structure must therefore be paired with function. A 2017 electron tomography study found post-cytokinesis plasmodesmata with no visible open cytoplasmic sleeve, yet detected macromolecular diffusion. The imaged arrangement and the movement assay supply different evidence about the same interface.[ref]
Architecture and permeability of post-cytokinesis plasmodesmata lacking cytoplasmic sleeves by William J. Nicolas and others. Abstract: membrane architecture and retained macromolecular transport
William J. Nicolas 2026-11-05
William J. Nicolas has investigated cellular membrane architecture using three-dimensional electron microscopy. He is the first author of the 2017 study reconstructing plasmodesmata and comparing their structure with their capacity for intercellular transport.[ref]
A plasmodesma contains a strand of endoplasmic reticulum within its enclosing cell membrane. Electron tomography showed that newly formed channels after cytokinesis could have such close membrane contact that an open cytoplasmic sleeve was not visible. Later cell differentiation and expansion were associated with a changed arrangement. Yet the newly formed structures still permitted movement of macromolecules.[ref]
Architecture and permeability of post-cytokinesis plasmodesmata lacking cytoplasmic sleeves by William J. Nicolas and others. Abstract: developmental membrane remodeling and macromolecular diffusion
The result makes a useful scientific distinction: an image of an apparent opening and a measurement of plasmodesmal permeability are not interchangeable. Structural reconstruction describes the organization captured by the imaging method; a transport assay tests whether a defined molecule actually moves between cells. Combining these observations challenged a simple identification of a visibly open sleeve with all intercellular exchange.
Nicolas's contribution in this work connects spatially resolved membrane structure with a functional transport measurement, rather than treating plasmodesmata as featureless holes in a cell wall.
Homepage: www.wjnicolas.com/