MORPHOGENESIS OF CROWN
GALL
67
the DNA content of a diploid nucleus in telophase. The most accurate
method of studying this so-called somatic polyploidy is to measure
spectrophotometrically the DNA content of the nuclei. Such measurements have, indeed, been made in different plant tissues (cf. Swift, 1953),
and the results show that the nuclei in differentiated cells in many cases
fall into distinct classes, 2C, 4C, 8C, and so on. It is of interest that some
resting nuclei remain at the 2C level (e.g., Patau, 1952; Nay lor, 1958),
for this means that nuclei have to undergo a DNA synthesis before they
are able to divide.
The effects of wounding have been much less studied by means of DNA
measurements. The most extensive investigation is the paper by Rasch
et al. (1959) who in Vicia faba compared sterile wounds with wounds
inoculated with Agrobacterium
tumefaciens.
In the unwounded stem the
following DNA classes were found: 2C, 4C, 8C, and 16C. During the
first 24 hr the DNA synthesis was equally activated in sterile and
infected wounds (the temperature at which the plants were kept is not
given). From the third day onward, the frequency of cells in DNA
synthesis was, however, higher in the tumor tissue. Diploid cells were
more readily induced to undergo DNA synthesis than cells in the higher
DNA classes. Rasch (1964) studied the DNA synthesis in the same
tissues by autoradiography with tritiated thymidine.
Most plant tissues respond to wounding with nuclear and cell division.
In the study by Rasch et al. (1959) on the broad bean, the mitotic
response in the sterile wound reached its peak on the third day. The
inoculated wound paralleled this up to the third day, but reached a maximum on the fifth day. Around the sterile wound the mitoses were back
to the starting point on the ninth day, whereas in the tumor they went
on as long as it kept growing.
It is not known, either in the wounded Vicia stems or other plant
organs, what proportion of the cells undergo a DNA synthesis before
mitosis. Most probably different plants and different tissues vary in this
respect. Patau and Das (1961) have shown that in cultures of tobacco
pith tissue—a situation in many ways comparable to wounding—about
half the cells undergo a DNA synthesis before mitosis, although others
enter mitosis without a DNA replication even after 16 days in culture.
It may be mentioned that differentiated cells in the onion roots, when
induced to divide with growth substances, also have been shown to do
so without a previous DNA synthesis (Partanen, 1965).
Similarly to DNA synthesis, mitosis is more easily induced in diploid
than in polyploid cells, either by wounding or by using growth substances
GALL
67
the DNA content of a diploid nucleus in telophase. The most accurate
method of studying this so-called somatic polyploidy is to measure
spectrophotometrically the DNA content of the nuclei. Such measurements have, indeed, been made in different plant tissues (cf. Swift, 1953),
and the results show that the nuclei in differentiated cells in many cases
fall into distinct classes, 2C, 4C, 8C, and so on. It is of interest that some
resting nuclei remain at the 2C level (e.g., Patau, 1952; Nay lor, 1958),
for this means that nuclei have to undergo a DNA synthesis before they
are able to divide.
The effects of wounding have been much less studied by means of DNA
measurements. The most extensive investigation is the paper by Rasch
et al. (1959) who in Vicia faba compared sterile wounds with wounds
inoculated with Agrobacterium
tumefaciens.
In the unwounded stem the
following DNA classes were found: 2C, 4C, 8C, and 16C. During the
first 24 hr the DNA synthesis was equally activated in sterile and
infected wounds (the temperature at which the plants were kept is not
given). From the third day onward, the frequency of cells in DNA
synthesis was, however, higher in the tumor tissue. Diploid cells were
more readily induced to undergo DNA synthesis than cells in the higher
DNA classes. Rasch (1964) studied the DNA synthesis in the same
tissues by autoradiography with tritiated thymidine.
Most plant tissues respond to wounding with nuclear and cell division.
In the study by Rasch et al. (1959) on the broad bean, the mitotic
response in the sterile wound reached its peak on the third day. The
inoculated wound paralleled this up to the third day, but reached a maximum on the fifth day. Around the sterile wound the mitoses were back
to the starting point on the ninth day, whereas in the tumor they went
on as long as it kept growing.
It is not known, either in the wounded Vicia stems or other plant
organs, what proportion of the cells undergo a DNA synthesis before
mitosis. Most probably different plants and different tissues vary in this
respect. Patau and Das (1961) have shown that in cultures of tobacco
pith tissue—a situation in many ways comparable to wounding—about
half the cells undergo a DNA synthesis before mitosis, although others
enter mitosis without a DNA replication even after 16 days in culture.
It may be mentioned that differentiated cells in the onion roots, when
induced to divide with growth substances, also have been shown to do
so without a previous DNA synthesis (Partanen, 1965).
Similarly to DNA synthesis, mitosis is more easily induced in diploid
than in polyploid cells, either by wounding or by using growth substances