The positional control of mitosis and cytokinesis in higher-plant cells |
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Authors: | M I Giménez-Abián L Utrilla J L Cánovas G Giménez-Martín M H Navarrete C De la Torre |
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Institution: | (1) Centro de Investigaciones Biológicas, CSIC, Velázquez 144, E-28006 Madrid, Spain, ES;(2) Departamento de Biología, Universidad Autónoma de Madrid, Canto Blanco, E-28049 Madrid, Spain, ES |
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Abstract: | The present work establishes a correlation between cell length and patterns of mitotic microtubular assemblies in Allium cepa L. root meristems. Binucleate cells were formed by a short caffeine treatment which aborted the formation of the phragmoplast
during telophase. The largest binucleate cells (about 50 μm in length) behaved as two contiguous mononucleate cells in their
next mitosis: they developed two preprophase bands (PPBs), one around each nucleus, where two spindles and two phragmoplasts
were subsequently formed. On the other hand, the shortest binucleate cells (about 36 μm in length) formed a single PPB at
the site of the aborted phragmoplast and, in the medium-sized cells (about 44 μm) in which the single PPB formed around the
nucleus possessing the largest cytoplasmic environment, the two mitotic spindles and the new phragmoplasts moved to, or were
assembled in the position of the phragmoplast that had been aborted one cycle earlier. Some rules derive from these observations.
First of all, the aborted phragmoplast left a signal for microtubule positioning which was still operative one cycle later,
in two-thirds of the bimitoses. Also, that formation of the PPB is dispensable. Moreover, its development does not always
predict the future division plane, because of the presence of competing old signals which are stronger than those shed by
the PPB in the same mitosis, but which fade away with distance. Finally, the positional signals were reinforced when the ratio
of monomeric to fibrillar actin was increased by cytochalasin D during their shedding. When this drug was given simultaneously
with caffeine, the frequency of bimitoses which, one cycle later, developed spindles and phragmoplasts in the positions of
the old phragmoplast increased. On the other hand, those frequencies dropped in relation to control when the cytochalasin
D treatment took place during bimitosis, indicating that at this time the treatment reinforced the signals produced in bimitosis
itself.
Received: 3 February 1997 / Accepted: 4 June 1997 |
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Keywords: | : Actin Allium Mitotic spindle Phragmoplast Preprophase Tubulin |
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