70
SIRKKA KUPILA-AHVENNIEMI AND EEVA THERMAN
1956). Occasionally these polyploid nuclei divide and then continue to
do so without reverting to endoreduplication.
As after wounding, the nuclei seen in mitosis in crown gall show different degrees of polyploidy in different plants. Thus in the tomato
only tetraploid nuclei seem to divide (Kupila, 1958), in the pea 16-ploid
divisions have been observed, in the broad bean 32-ploid ones, and in
the tobacco possibly even higher polyploids occasionally undergo mitosis
(Kupila and Therman, 1962). In the first mitosis after repeated DNA
synthesis the chromosomes appear as diplochromosomes or as more
multiple chromatid bundles. In the pea this is seen only in prophase,
the bundles presumably falling apart before metaphase, but in the other
plants mentioned the diplochromosomes also appear in metaphase.
Very highly polyploid nuclei are often lobulated, to the extent of
resembling "grape clusters" (Therman, 1956). It is not surprising that
these lobulated nuclei in the past have been interpreted as several
separate nuclei, thus giving rise to the idea of multinucleate cells. The
giant nuclei often exhibit high numbers of nucleoli—22 in one tobacco
cell (Kupila and Therman, 1962)—and, for instance, in the broad bean,
numerous large chromocenters.
The only mitotic abnormalities in crown gall seem to be caused by the
irregularities that affect the orientation and division of diplochromosomes
or larger chromatid bundles. Chromosomes in normal, differentiated cells
often suffer from structural changes (cf. Therman, 1951), and these can,
of course, be inherited by the crown gall cells descending from them.
Obviously they would have no connection with tumorigenesis.
In the crown gall of the sunflower the cells remain diploid. As a result
the tumor tissue consists of even-sized cells as compared with the galls
in other hosts in which the cell and nuclear sizes show an enormous
range of variation. That the crown gall tissue even of the sunflower is
able to respond by cell growth to artificially high concentrations of
growth substances has been shown by Struckmeyer et al. (1949). Unfortunately no attention was paid to the nuclear sizes or to the chromosomes in this study.
The claim of Rasch et al. (1959) that nuclei in the higher DNA classes
are reduced to the diploid level through repeated division without intervening DNA synthesis has been dealt with by Kupila (1963). Suffice it
to point out that in the case of a nucleus with a polyploid chromosome
number, reduction would seem to require somatic pairings, which is
virtually absent in higher plants. In the case of a nucleus with a diploid
SIRKKA KUPILA-AHVENNIEMI AND EEVA THERMAN
1956). Occasionally these polyploid nuclei divide and then continue to
do so without reverting to endoreduplication.
As after wounding, the nuclei seen in mitosis in crown gall show different degrees of polyploidy in different plants. Thus in the tomato
only tetraploid nuclei seem to divide (Kupila, 1958), in the pea 16-ploid
divisions have been observed, in the broad bean 32-ploid ones, and in
the tobacco possibly even higher polyploids occasionally undergo mitosis
(Kupila and Therman, 1962). In the first mitosis after repeated DNA
synthesis the chromosomes appear as diplochromosomes or as more
multiple chromatid bundles. In the pea this is seen only in prophase,
the bundles presumably falling apart before metaphase, but in the other
plants mentioned the diplochromosomes also appear in metaphase.
Very highly polyploid nuclei are often lobulated, to the extent of
resembling "grape clusters" (Therman, 1956). It is not surprising that
these lobulated nuclei in the past have been interpreted as several
separate nuclei, thus giving rise to the idea of multinucleate cells. The
giant nuclei often exhibit high numbers of nucleoli—22 in one tobacco
cell (Kupila and Therman, 1962)—and, for instance, in the broad bean,
numerous large chromocenters.
The only mitotic abnormalities in crown gall seem to be caused by the
irregularities that affect the orientation and division of diplochromosomes
or larger chromatid bundles. Chromosomes in normal, differentiated cells
often suffer from structural changes (cf. Therman, 1951), and these can,
of course, be inherited by the crown gall cells descending from them.
Obviously they would have no connection with tumorigenesis.
In the crown gall of the sunflower the cells remain diploid. As a result
the tumor tissue consists of even-sized cells as compared with the galls
in other hosts in which the cell and nuclear sizes show an enormous
range of variation. That the crown gall tissue even of the sunflower is
able to respond by cell growth to artificially high concentrations of
growth substances has been shown by Struckmeyer et al. (1949). Unfortunately no attention was paid to the nuclear sizes or to the chromosomes in this study.
The claim of Rasch et al. (1959) that nuclei in the higher DNA classes
are reduced to the diploid level through repeated division without intervening DNA synthesis has been dealt with by Kupila (1963). Suffice it
to point out that in the case of a nucleus with a polyploid chromosome
number, reduction would seem to require somatic pairings, which is
virtually absent in higher plants. In the case of a nucleus with a diploid