64
SIRKKA KUPILA-AHVENNIEMI AND EEVA THERMAN
The inhibition of tumor formation in the rapidly growing meristematic
tissue is often mentioned in connection with the hypotheses on the nature
of tumor transformation. It seems, however, obvious that not enough
experiments have been done to solve the problem at which stage of
development normal plant cells can be transformed into tumor cells.
Some preliminary experiments along these lines have recently been
performed in Kupila-Ahvenniemi's laboratory and the results have
indicated that the crown gall effect can be observed closer to the root
tip than had been assumed.
Considering the range of variation in the wound reaction, it is not
surprising that the anatomy of crown gall in different host species shows
great differences. Not all the dicots are able to form a wound cambium
and not all dicots tend to regenerate conductive tissue around a wound.
Usually, the experiments have been made on the most reactive species.
It seems probable that studies comparing the wound reaction and the
crown gall development in the plants with a high regenerative capacity
to others with a low capacity might throw more light on the crown gall
problem.
B. Cytological Aspects
1. Submicroscopic
Observations
The wound reaction has received relatively little attention on the
electron microscopic level. Ryter and Manigault (1964) have given a
short description of the behavior of cells around a sterile wound in
connection with a study on the crown gall. No immediate reaction to the
wounding is apparent, the structure of the cytoplasm stays poor, and
the vacuoles fill the greater part of the cell. The walls show a layered
structure. Greater changes are apparent in the small cells that result
from the divisions induced by wounding. The cell walls are lined with
dense cytoplasm with a well-developed ergastoplasm and a number of
mitochondria and plastids. At earlier stages, the authors did not observe
any ribosomes, but ribosomes do appear in the newly formed cells. No
differences can be observed between the inner structure of the cells
reacting to sterile wounding and of cells transformed to tumor cells.
However, the wall structure of the tumor cells appears changed. Canals,
apparently caused by changes in wall material and a thinning in wall
structure, become apparent and are sometimes observed to spread in
the level of the middle lamellae. Dense, granulated material lines the
SIRKKA KUPILA-AHVENNIEMI AND EEVA THERMAN
The inhibition of tumor formation in the rapidly growing meristematic
tissue is often mentioned in connection with the hypotheses on the nature
of tumor transformation. It seems, however, obvious that not enough
experiments have been done to solve the problem at which stage of
development normal plant cells can be transformed into tumor cells.
Some preliminary experiments along these lines have recently been
performed in Kupila-Ahvenniemi's laboratory and the results have
indicated that the crown gall effect can be observed closer to the root
tip than had been assumed.
Considering the range of variation in the wound reaction, it is not
surprising that the anatomy of crown gall in different host species shows
great differences. Not all the dicots are able to form a wound cambium
and not all dicots tend to regenerate conductive tissue around a wound.
Usually, the experiments have been made on the most reactive species.
It seems probable that studies comparing the wound reaction and the
crown gall development in the plants with a high regenerative capacity
to others with a low capacity might throw more light on the crown gall
problem.
B. Cytological Aspects
1. Submicroscopic
Observations
The wound reaction has received relatively little attention on the
electron microscopic level. Ryter and Manigault (1964) have given a
short description of the behavior of cells around a sterile wound in
connection with a study on the crown gall. No immediate reaction to the
wounding is apparent, the structure of the cytoplasm stays poor, and
the vacuoles fill the greater part of the cell. The walls show a layered
structure. Greater changes are apparent in the small cells that result
from the divisions induced by wounding. The cell walls are lined with
dense cytoplasm with a well-developed ergastoplasm and a number of
mitochondria and plastids. At earlier stages, the authors did not observe
any ribosomes, but ribosomes do appear in the newly formed cells. No
differences can be observed between the inner structure of the cells
reacting to sterile wounding and of cells transformed to tumor cells.
However, the wall structure of the tumor cells appears changed. Canals,
apparently caused by changes in wall material and a thinning in wall
structure, become apparent and are sometimes observed to spread in
the level of the middle lamellae. Dense, granulated material lines the