Plant Spindle Fiber Origins

name        Danbi
status       student
location

Question -   My teacher told me that in the process of Mitosis
in plants, where the spindle fibres are formed has not been yet
identified. (since plants don't have centrioles) Is this true?
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Your teacher is correct that most plant cells, as well as fungi, do
not contain distinct centrioles, as such.  But microtubular spindle
fibers and a mitotic process comparable to that of animal cells are
still observable.  Microtubule assembly is initiated by
'microtubule-organizing centers' (MTOC), which consist of
'pericentriolar material', including -tubulin, and are
distributed around the nuclear envelope.  The online textbook,
'Molecular Cell Biology', briefly summarizes these unique properties
of plant cell mitosis:

http://www.ncbi.nlm.nih.gov/books/bv.fcgi?rid=mcb.section.5499#5502

Unfortunately, the accompanying Figure 19-38 is unavailable for
viewing online.  However, I do have a print version of this textbook
with copy of the figure.  It shows that migration of the sister
chromatids to opposite poles of the mitotic spindle is very similar to
that of animal cells.  The main difference appears to be that the
chromatids are not as concentrated as if they were attracted to a
single centriole, like in animal cells.

But the more noticeable difference is in how the shape of the plant
cell doesn't change as much as an animal cell does because it's
surrounded by the rigid cell wall, as descibed in the 'Molecular Cell
Biology' summary.  Perhaps this reduced change in shape might help to
explain why centrioles are not as necessary for plant cell mitosis.
Since mitotic plant cells don't elongate as much as animal cells, the
chromatids might not need to migrate as strongly toward opposites
poles of the mitotic spindle to still maintain their efficient
distribution into the plant daughter cells.

Thanks for the great question,

Jeff Buzby, Ph.D.
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