48
SIRKKA KUPILA-AHVENNIEMI AND EEVA THERMAN
making them susceptible to the crown gall organism. Rack (1954)
damaged plant tissue by burning or by freezing and proved that in both
cases the cells surrounding the wound became sensitive to the bacterial
effect. He also experimented with acids and alkali. The treatment with
acid is too drastic and harms the whole plant, whereas the treatment
with alkali leads to the formation of galls after a bacterial inoculation.
The work of Riker (1923a) and others has shown (cf. Braun and
Stonier, 1958) that the size of the tumor is dependent on the size of the
wound. Hildebrand (1942) demonstrated that a wound of 3 ju,
2
was too
small to allow tumor formation in the tomato. One or more epidermal
cells had to be injured for any galls to develop. Lippincott and Heberlein
(1965) have indicated that sprinkling No. 400 grit Carborundum on the
leaves of the pinto bean and gently rolling a glass rod over them brings
about wounds big enough for the tumor formation to take place in the
presence of bacteria.
At present the most widely accepted idea is that the wounding causes
certain physiological changes in the cells around the wound as a result
of which they become sensitive to the bacterial effect. The term "conditioning," originally used by Braun and Mandle (1948) and Braun
(1952), has been accepted to indicate the series of metabolic events that
must take place in the cells before the bacteria can induce a transformation in them. The conditioning is a gradual process, the degree of which
first increases then decreases (Braun, 1952; Lipetz, 1966). The cells
remain in the conditioned state only for a certain length of time; after
this they cease to be sensitive. In the words of Braun (1962, p. 536): "It
is only during a relatively few hours in the normal wound healing cycle
that the normal cells can be transformed into tumor cells of the most
rapidly growing type. Predisposition of the host cells to transformation
is, then, a transient character, the nature of which has not yet been
elucidated."
The importance of the conditioning has been demonstrated by Braun
in a number of studies (cf. Braun and Stonier, 1958). These were based
on Riker's (1926) observation that smaller tumors developed at 28°30°C than at lower temperatures, and that temperatures above 30°C were
outright inhibitory. The inhibition of gall formation by high temperatures provided a tool to determine the exact interval in the woundhealing process during which the host cells were susceptible to the
tumorigenic effect. The plants are kept at 32°C, which has an inhibitory
effect on the tumor induction, and are then moved into the advantageous
temperature of about 25°C for the necessary time. Another useful
SIRKKA KUPILA-AHVENNIEMI AND EEVA THERMAN
making them susceptible to the crown gall organism. Rack (1954)
damaged plant tissue by burning or by freezing and proved that in both
cases the cells surrounding the wound became sensitive to the bacterial
effect. He also experimented with acids and alkali. The treatment with
acid is too drastic and harms the whole plant, whereas the treatment
with alkali leads to the formation of galls after a bacterial inoculation.
The work of Riker (1923a) and others has shown (cf. Braun and
Stonier, 1958) that the size of the tumor is dependent on the size of the
wound. Hildebrand (1942) demonstrated that a wound of 3 ju,
2
was too
small to allow tumor formation in the tomato. One or more epidermal
cells had to be injured for any galls to develop. Lippincott and Heberlein
(1965) have indicated that sprinkling No. 400 grit Carborundum on the
leaves of the pinto bean and gently rolling a glass rod over them brings
about wounds big enough for the tumor formation to take place in the
presence of bacteria.
At present the most widely accepted idea is that the wounding causes
certain physiological changes in the cells around the wound as a result
of which they become sensitive to the bacterial effect. The term "conditioning," originally used by Braun and Mandle (1948) and Braun
(1952), has been accepted to indicate the series of metabolic events that
must take place in the cells before the bacteria can induce a transformation in them. The conditioning is a gradual process, the degree of which
first increases then decreases (Braun, 1952; Lipetz, 1966). The cells
remain in the conditioned state only for a certain length of time; after
this they cease to be sensitive. In the words of Braun (1962, p. 536): "It
is only during a relatively few hours in the normal wound healing cycle
that the normal cells can be transformed into tumor cells of the most
rapidly growing type. Predisposition of the host cells to transformation
is, then, a transient character, the nature of which has not yet been
elucidated."
The importance of the conditioning has been demonstrated by Braun
in a number of studies (cf. Braun and Stonier, 1958). These were based
on Riker's (1926) observation that smaller tumors developed at 28°30°C than at lower temperatures, and that temperatures above 30°C were
outright inhibitory. The inhibition of gall formation by high temperatures provided a tool to determine the exact interval in the woundhealing process during which the host cells were susceptible to the
tumorigenic effect. The plants are kept at 32°C, which has an inhibitory
effect on the tumor induction, and are then moved into the advantageous
temperature of about 25°C for the necessary time. Another useful