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Botaniska Notiser 1947, Häfte ’2. Lund
Smärre uppsatser och meddelanden.
Proximal heterochromatin, structure of the centromere and
the mechanism of its misdivision.
So läs studies ön the structure of the centromere hy means of two new
methods elaborated hy the present writer about a year and a half ago have
now reached a stage when a brief report may be justified. These methods
have chiefly been applied to root-tip mitoses of Hyacinthus orientalis but
also work ön other materials as Allium Cepa. They allow of a clear
demonstration of the actively mobile component of the centromere.
First m e t h o d. Fixation in mixtures of glvcerol (or ethylene glycol),
acetic acid and water (2 : 1 : t or 1 : t : t) is followed bv hardening in
chrome-acetic-formalin before dehydration, embedding and microtome sectioning. The
cytoplasmic shrinkage caused by the glvcerol is a disadvantage but is tolerable.
The chromosome are somewhat swollen and have a com])letely smooth and
even outline. Stained with crystal violet the slides show a strong contrast
between the nearly unstained chromosome body and distinct dark
differentia-tions in the centromere region appearing like and no doubt identical with the
»spindle spherules» of Schrader (Chromosoma 1: 230—237, 1939). When the
chromosome is stained with Feulgen, (here is not a trace of such a differential
staining, it is as usual stained all over. A double staiu with blue spindle
spherules ön red chromosomes cail be obtained by combining crystal violet
with Feulgen.
Se co nd method. The root tips are killed by agents having only
a verv mild influence ön the cell constiluents from a chemical point of view
(not to be confused with agents having a good preservative action ön the
morphological cell structure, quite a different aspect), such as 50 °/o glvcerol
or a saturated aqueous solution of toluene. After the glvcerol treatment the
root tips are stored for some hours in distilled water. When toluene is used
|hey cail remain in the same solution. After that they are fixed in
chrome-acetic-formatin, embedded and sectioned. This method gives quite a different
result from the preceding one. The chromosome body is often completely
dissolved, leaving the spindle spherules alone undissolved and formiug a
metaphase plate or an anaphase group of their own. The fibrous structure of
the spindle is often preserved and it cail be seen that the chromosomal spindle
fibres are attached to the spindle spherules. Levan and Steinegger (1947.
Hereditas 33. in the press) have quite recently got the same effect by certain
concentrations of chloroform in water solution, and 1 think that it should be
possible also to use many other fat solvents (or other narcotics) instead of
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