= Plasmodesma
= Plasmodesmata
{synonym}
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.<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]{ref}
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.<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]{ref}
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.<Architecture and permeability of post-cytokinesis plasmodesmata lacking cytoplasmic sleeves by William J. Nicolas and others>[Abstract: post-cytokinesis structure and macromolecular permeability]{ref}
An original comparison would score channel number, three-dimensional structure and transfer of a defined tracer separately. Equal channel counts do not guarantee equal exchange, and passage of one tracer does not establish unrestricted passage of every <protein>.
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