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Symplast/Apoplast/Protoplast

nigel at pathos nigel at pathos
Tue Jul 7 01:28:15 EST 1992


In article <3667 at news.duke.edu|-> una at phy.duke.edu (Una Smith) writes:
|->
|->I read an interesting paper today.  The authors wrote:
|->"The assertions made in this paper are summarized in Table 1."
|->Here it is:
|->
|->Table 1.  Philosophical assertions concerning plant "cellularity."
|->Assertions f-i provide the principal foci for biomechanical analysis
|->of plants.
|->
|->a.     The concepts of the organism and the cell are logically
|->       independent of one another.
|->b.     Multicellularity is not a requisite condition for the
|->       expression of morphological complexity.
|->c.     Multicellularity is the result of a highly specialized
|->       developmental scheme in which cytokinesis and nuclear
|->       divisions are precisely correlated.
|->d.     The protoplasm is the fundamental organismic unit.
|->e.     In multicellular plants, the protoplasm is incompletely
|->       partitioned by an apoplastic (cell wall) infrastructure.
|->f.     In addition to providing an opportunity for the physiologic
|->       and reproductive specialization of the protoplasm, the
|->       apoplastic infrastructure provides mechanical support.
|->g.     The apoplast is a shared-primitive condition in all plants,
|->       i.e., unicellular, colonial and multicellular organisms
|->       have an apoplastic-symplastic structure.
|->h.     The "internalization" of the apoplast has occurred in at
|->       least two different ways (siphonous and multicellular plants).
|->i.     Only one of these (multicellularity) permits the acquisition
|->       of large size in a terrestrial habitat.
|->j.     Multicellularity was an exaptation for the colonization of
|->       land by plants.


|->I am curious as to why the authors use the term "protoplasm"
|->to refer, apparently, to the entire (multicellular) organism,
|->rather than "individual".  I am confused about what the term
|->"individual" means when applied to plants.  Any comments?


Trust me.. if Don had meant to say "individual", you would have heard him.

The basic idea is that the plant is made up of the symplast and the apoplast.
Where symplast = all the cytoplasm in all the cells; interconnected by 
plasmodesmata (like gap junctions in animals).  

The appoplast on the other hand is all the stuff outside the plasma membrane...
all the "dead" stuff. (You know, like cell walls and xylem elements)

I would define the protoplasm = all the stuff inside the protoplast = all
the stuff inside the plasma membrane.  I think we would both agree that this 
is only part of the "individual" plant.
(the other part being that which is outside the protoplast = the apoplast)
 
What you end up with is a picture of cell that is much like many modern offices
(great big room with lots of dividers) the space on a given floor appears to be
divided into many separate rooms, but on closer inspection is obviously a
contiguous space.


hope this helps.

-nigel



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