MORPHOGENESIS OF CROWN
GALL
49
method in the earlier studies was based on the ability of certain plants
to survive temperatures high enough to kill the bacteria and the fact
that the tumors, once initiated, continued their growth when the plants
were moved back to normal conditions. A number of studies indicated
that the tumors were not initiated during the first 24 hr after wounding.
Also, if the inoculation was made after the wound healing had proceeded
for 5 days no galls were formed. Very small tumors were produced both
during the 30-34 hr and during the 90-96 hr period following wounding.
The optimal period for rapidly growing tumors appeared to be around
60 hr after wounding. The conclusion was that certain metabolic changes
had to take place in the host cells, i.e., they needed to be conditioned,
before the transformation was possible. It did not seem to matter whether
the plants were kept at 24° or at 32°C during the conditioning. The
minimum time needed by the bacteria to induce the cell transformation
was shown to be 10 hr. However, bigger and more rapidly growing
tumors were produced with a prolonged bacterial treatment.
Recently the dependence of the rate of conditioning on the temperature has been studied more extensively. Kupila and Stern (1961) were
the first to stress the significance of the temperature for the rate of
DNA synthesis in wounded and in crown gall tissue. Lipetz (1965,
1966) questioned the assumption that the wound-healing processes and,
thus, the conditioning proceeded at equal speed in different temperatures. He placed wounded Kalanchoe
daigremontiana
plants in growth
chambers maintained either at 25° or 32°C (Lipetz, 1965). The formation
of the wound cambium was observed to start about 12 hr earlier in the
plants at 32°C than in comparable plants at 25°C. To confirm that this
difference in the speed of wound healing also meant a difference in the
rate of conditioning, Lipetz wounded Kalanchoe
plants and kept them
at 25° or 32°C for 3, 6, 9, or 16 hr before inoculation. After inoculation,
the bacteria were allowed to act for 24 hr before the plants were placed
in 32°C which prevented further tumor induction. The tumor sizes after
3 weeks showed that conditioning the plants at 32°C for a certain
number of hours rendered them more sensitive to the bacterial effect than
conditioning at 25°C for the same length of time. Thus the processes
taking place during the conditioning were apparently temperaturedependent. Another study by Lipetz (1966) included the temperature
36°C in addition to 25° and 32°C. The results confirmed that the wound
healing and the conditioning were correlated and were both dependent
on the temperature. Lipetz found that the time between wounding and
the first oriented cell divisions was linearly and inversely related to the
GALL
49
method in the earlier studies was based on the ability of certain plants
to survive temperatures high enough to kill the bacteria and the fact
that the tumors, once initiated, continued their growth when the plants
were moved back to normal conditions. A number of studies indicated
that the tumors were not initiated during the first 24 hr after wounding.
Also, if the inoculation was made after the wound healing had proceeded
for 5 days no galls were formed. Very small tumors were produced both
during the 30-34 hr and during the 90-96 hr period following wounding.
The optimal period for rapidly growing tumors appeared to be around
60 hr after wounding. The conclusion was that certain metabolic changes
had to take place in the host cells, i.e., they needed to be conditioned,
before the transformation was possible. It did not seem to matter whether
the plants were kept at 24° or at 32°C during the conditioning. The
minimum time needed by the bacteria to induce the cell transformation
was shown to be 10 hr. However, bigger and more rapidly growing
tumors were produced with a prolonged bacterial treatment.
Recently the dependence of the rate of conditioning on the temperature has been studied more extensively. Kupila and Stern (1961) were
the first to stress the significance of the temperature for the rate of
DNA synthesis in wounded and in crown gall tissue. Lipetz (1965,
1966) questioned the assumption that the wound-healing processes and,
thus, the conditioning proceeded at equal speed in different temperatures. He placed wounded Kalanchoe
daigremontiana
plants in growth
chambers maintained either at 25° or 32°C (Lipetz, 1965). The formation
of the wound cambium was observed to start about 12 hr earlier in the
plants at 32°C than in comparable plants at 25°C. To confirm that this
difference in the speed of wound healing also meant a difference in the
rate of conditioning, Lipetz wounded Kalanchoe
plants and kept them
at 25° or 32°C for 3, 6, 9, or 16 hr before inoculation. After inoculation,
the bacteria were allowed to act for 24 hr before the plants were placed
in 32°C which prevented further tumor induction. The tumor sizes after
3 weeks showed that conditioning the plants at 32°C for a certain
number of hours rendered them more sensitive to the bacterial effect than
conditioning at 25°C for the same length of time. Thus the processes
taking place during the conditioning were apparently temperaturedependent. Another study by Lipetz (1966) included the temperature
36°C in addition to 25° and 32°C. The results confirmed that the wound
healing and the conditioning were correlated and were both dependent
on the temperature. Lipetz found that the time between wounding and
the first oriented cell divisions was linearly and inversely related to the