MORPHOGENESIS OF CROWN GALL
69
spectrophotometry measurements by Rasch et al. (1959). The cells in
an uninjured Vicia stem fall into straight DNA classes: 2C, 4C, 8C, and
16C. Both in the normal and the crown gall wound, intermediate DNA
classes appear which represent the S period.
The first mitoses follow soon the first wave of DNA synthesis. It
seems useless to recapitulate the information on the first appearance of
mitoses in different plants, since Lipetz (1965, 1966)—as discussed
earlier—has shown that temperature plays an important role in the
timing of the first cell divisions, and most of the earlier studies do not
pay any attention to it.
Concomitantly with the first cell divisions the cytoplasm seems to
increase in the cells around the crown gall wound (Therman, 1956;
Kupila, 1958; Rasch et al., 1959). The last-named authors also compared
cytochemically a normal and a crown gall wound, and came to the following conclusions: Both nucleolar and cytoplasmic ribonucleic acid (RNA)
and protein levels are significantly increased in the tumor cells as compared with normal wound cells. Nuclear histones, on the other hand, as
determined by fast green staining, do not seem to be increased relative to
the normal cells.
£>. The Developing
Crown Gall. Kupila (1963) has reviewed the older
observations on crown gall in the light of modern cytology. Suffice it here
to recall that of the various aberrations ascribed to crown gall, such as
amitosis, multinucleate cells, somatic reduction, and somatic polyploidy,
only the last has survived the test of time.
From the more recent analyses of crown gall cytology in the broad
bean (Therman, 1956; Rasch et al., 1959), the tomato, the pea, the sunflower (Kupila, 1956, 1958), and the tobacco (Kupila and Therman,
1962), the following picture emerges. The stems of all these hosts—with
the exception of the sunflower—show, in addition to diploid cells, cells
with various degrees of somatic polyploidy. The sunflower, on the other
hand, consists of diploid cells only.
In the crown gall the diploid cells are first to divide and during the
development of the tumor they continue to do so. Most of the tetraploid
cells behave in the same way. The great majority of the more highly
polyploid cells start to grow, reaching often giant sizes, whereas the
nucleus without dividing undergoes one DNA synthesis after another
(endoreduplication). Microspectrophotometric measurements in a 33day-old gall showed the highest DNA class in the broad bean to be 64C
(Rasch et al., 1959). However, when the tumor grows older some nuclei
obviously achieve much higher degrees of polyploidy (cf. Therman,
69
spectrophotometry measurements by Rasch et al. (1959). The cells in
an uninjured Vicia stem fall into straight DNA classes: 2C, 4C, 8C, and
16C. Both in the normal and the crown gall wound, intermediate DNA
classes appear which represent the S period.
The first mitoses follow soon the first wave of DNA synthesis. It
seems useless to recapitulate the information on the first appearance of
mitoses in different plants, since Lipetz (1965, 1966)—as discussed
earlier—has shown that temperature plays an important role in the
timing of the first cell divisions, and most of the earlier studies do not
pay any attention to it.
Concomitantly with the first cell divisions the cytoplasm seems to
increase in the cells around the crown gall wound (Therman, 1956;
Kupila, 1958; Rasch et al., 1959). The last-named authors also compared
cytochemically a normal and a crown gall wound, and came to the following conclusions: Both nucleolar and cytoplasmic ribonucleic acid (RNA)
and protein levels are significantly increased in the tumor cells as compared with normal wound cells. Nuclear histones, on the other hand, as
determined by fast green staining, do not seem to be increased relative to
the normal cells.
£>. The Developing
Crown Gall. Kupila (1963) has reviewed the older
observations on crown gall in the light of modern cytology. Suffice it here
to recall that of the various aberrations ascribed to crown gall, such as
amitosis, multinucleate cells, somatic reduction, and somatic polyploidy,
only the last has survived the test of time.
From the more recent analyses of crown gall cytology in the broad
bean (Therman, 1956; Rasch et al., 1959), the tomato, the pea, the sunflower (Kupila, 1956, 1958), and the tobacco (Kupila and Therman,
1962), the following picture emerges. The stems of all these hosts—with
the exception of the sunflower—show, in addition to diploid cells, cells
with various degrees of somatic polyploidy. The sunflower, on the other
hand, consists of diploid cells only.
In the crown gall the diploid cells are first to divide and during the
development of the tumor they continue to do so. Most of the tetraploid
cells behave in the same way. The great majority of the more highly
polyploid cells start to grow, reaching often giant sizes, whereas the
nucleus without dividing undergoes one DNA synthesis after another
(endoreduplication). Microspectrophotometric measurements in a 33day-old gall showed the highest DNA class in the broad bean to be 64C
(Rasch et al., 1959). However, when the tumor grows older some nuclei
obviously achieve much higher degrees of polyploidy (cf. Therman,