The remarkable results of the application of
colchicine to plants, first described in 1937, have
stimulated many investigations on the induction of
polyploidy with this drug. A great number of
scientific reports on its action have been published.
Altogether more than one hundred genera and two
hundred and fifty species of plants have been treated,
and a number of polyploid crop plants of economical
value has been established during the period 1937 to
1942. Many other chemicals have also been tested,
and some have been found to produce similar results, the most effective being
acenaphthene and some plant growth substances
(auxins) like indolyl -3- acetic acid, indolyl -3-
butyric acid, and naphthalene-1-acetic acid.
The effects of colchicine treatment on plants
comprise chromosome doubling, irregular distribution
of chromosomes, and chromosome fragmentation, all of
which might be connected with some heritable changes
in the plant. In addition to these, tissue hyper-plasia, increase of cell size, and excessive contrastion
of chromosomes may also occur.
The mechanism of chromosome duplication was
attributed to inhibition of the spindle formation and
delay in the division of the centromeres. Thus
although the chromosomes divided they failed to
separate, and remained together until a new nuclear
membrane was formed. The process could be repeated
a number of times during the course of treatment,
provided the chromosomes retained their capacity for
division. If part of the treated tissue
was not affected, or some of the affected cells
returned to the diploid state after the action of
colchicine ceased, a rnixoploid tissue resulted.
When the polyploid cells divided continuously, a
polyploid tissue or plant might be formed. The great
disadvantage of this kind of autotetraploid tissue or
plant, induced from an ordinary plant, was the
sterility of reproductive cells, which limited
further investigation and the commercial exploitation
of the induced polyploid. On the contrary, the
amphidiploid or allotetraploid, induced from the
sterile F₁ of either interspecific or intergeneric
cross, was fertile.
Owing to the inhibition of the spindle formation
and the activity of centromeres in the treated cells,.
the daughter chromosomes spread in disorderly fashion.
and failed to congregate on the enuatorial plate.
When the spindle was restored, if some of the chromosomes
were still not able to go the poles, or the
whole complement of chromosomes was divided into
groups by the pressure of the cellular or nuclear
division, an irregular distribution of chromosomes
to the daughter nuclei or cells occurred. In this case, it was possible to produce chromosome
deficiency and chromosome duplication among the cells
in subsequent generations, although the
cells containing an irregular number of chromosomes
possessed very little capacity of division,. When
the polyploid cells, either euploid or aneuploid,
multiplied themselves along with the normal diploid
cells in one plant, a chimerical plant resulted.
The breakage or fragmentation of chromosomes
induced by colchicine was reported by Eigsti
and Krythe. Karpechenko found that some
of the chromosomes in the treated materials broke
into two parts exactly at the point of attachment of
the centromere. This indicated that the effect of
the colchicine treatment might have been something
more than the alteration of chromosome numbers.
In contrast to the ready production of polyploiids
in plants, colchicine has not been so effective in
animals. Nevertheless, there are numerous indications
that the primary action of the substance, that is, the
destruction of the spindle, occurs also in animal cells.
This does not, however, lead to the formation of polyploid cells as readily in animals as it does in plants,
though occasionally polyploids are produced. In the
following section, the findings of previous workers
who investigated the treatment of animal tissues with
colchicine are reviewed, from which it will be seen
that the production of polyploid cells in higher
animals is not to be regarded as impossible. Experiments
with colchicine on the sex cells of mice form
the basis of this thesis and conclusions as to the
action of colchicine on the mechanics of cell division
have been drawn. From the experimental results, it
will be seen that the production of functional polyploid spermatogonia and spermatocytes, that is,
induction of polyploid sex cells which still have the
capacity of multiplication, is possible, and the
application of colchicine or other polyploidyinducing
substances may be of importance in the
animal as well as the botanical field.