Question from my students: antipodal cell and food storage

Ross Koning koning at ECSUC.CTSTATEU.EDU
Sat Nov 15 17:25:01 EST 1997


At 3:54 PM -0500 11/14/97, Shinhan Shiu wrote:

>Does anybody know the function(s) of antipodal cell in the embryo sac of
>Angiosperms?

I know of no function for them.  I see them as relics
of a multicellular gametophyte that has become reduced
through evolution and taken into more and more covering
layers (integument, ovary, receptacle--in the case of
inferior ovaries at least).

>Also, the food reserve in most seeds is either stored in the cotyledon or
>endosperm (any
>other place? examples?). My students asked me if there were any kind of
>selective
>advantage or "evolutionary superiority" of either of those two. We had an
>active
>discussion.

The discussion was probably more helpful than any one
"answer" could be.  Logically I would expect that
moving the storage material into the embryo (usually
cotyledon(s)) puts the reserves closer to the areas
needing them later.  Thus, when seed germination is
triggered, the embryo just has to re-distribute these
reserves as needed.  Having the reserves in an external
endosperm means that at germination time, these have
to be depolymerized externally, accumulated by the
embryo, then distributed internally.  The chance of
loss of monomers and the speed of response in this
external process seems to me to be less-advantageous.
Yet, some of the most successful plants on earth have
endosperm rather than huge cotyledons...so there must
be reasons why both can be advantageous under certain
(but perhaps disparate) circumstances.  One idea for
external endosperm that comes to mind is this; maybe
if you have internal reserves the risk of becoming a
target of herbivory is increased.  A moderate attack
on part of an external supply would leave the intact
embryo at least something to go on.  The partially attacked
embryo of the cotyledon-storage model might be damaged
beyond a normal growth response.  Probably these and
other ideas germinated in your discussion.  That helps
students more than having an "answer" on the tip of your
tongue.  It gets them to start thinking like scientists.
How might you test these possibilities?  That leads to
some really fruitful discussions...and maybe a thesis
project.

ross

_______________________________________________________________
Ross Koning                 | koning at ecsu.ctstateu.edu
Biology Department          | http://koning.ecsu.ctstateu.edu/
Eastern CT State University | phone: 860-465-5327
Willimantic, CT 06226 USA   | fax: 860-465-4479
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