MORPHOGENESIS OF CROWN
GALL
63
In the primary leaves of the pinto bean, Lippincott and Heberlein
(1965) produced tumors by sprinkling the leaves with Carborundum,
placing a few drops of bacterial solution on the leaves, and rubbing the
leaf surface with a glass rod. This resulted in the formation of rather
small, superficial wounds. The authors observed the tumors first as small
chlorotic outgrowths projecting above the leaf surface. Later the leaf
blade lost its color while the tumors became green. A microscopic study
of tumor development revealed that, as a result of the Carborundum
treatment, a number of epidermal cells had died. Cells of the palisade
parenchyma directly under these divided, and this stimulus spread to the
spongy parenchyma. The minor vascular elements associated with the
developing tumors enlarged and became distorted. Small groups of xylem
cells were found without any connection with the normal vascular
system. The well-developed tumors contained small, heavily stained cells,
disorganized tracheids and, outside the smaller cells, a number of
enlarged cells.
3. Comparison of Wound and Crown Gall Tissue
Only in a few recent studies have the wounded and the crown gall
tissues been compared in the same plant (Bopp and Leppla, 1964;
Lippincott and Heberlein, 1965; Lipetz, 1966). Otherwise, the comparison
between these two tissues can only be based on their general characteristics.
It is interesting that the crown gall development is inhibited in the
monocots, which show none or a weak reaction to wounding, as well as
in the meristematic tissues of the stem and the root tips of dicots, which
show a remarkably strong regenerative power. It could be speculated
that the lack of reactivity in the monocots is correlated with the lack of
ability to continued cell division in their differentiated tissues. However,
some monocots do react to wounding and at least in these plants the
prerequisites for conditioning might be expected to exist. Restudy of the
wound and the crown gall reactions in certain selected monocots might
yield interesting results. In this connection, the question of the reactivity of different cell types in the dicots is of importance. Certain cell
types are reactive, whereas others react slowly, or not at all, to wounding.
The same phenomenon has been described repeatedly in studies dealing
with crown gall. However, it is not certain that the cells react similarly
to both agents. The report of Bopp and Leppla (1964) that the pith of
the Kalanchoe stem proliferates vigorously after wounding but does not
take part in the tumor formation, is a good example of this.
GALL
63
In the primary leaves of the pinto bean, Lippincott and Heberlein
(1965) produced tumors by sprinkling the leaves with Carborundum,
placing a few drops of bacterial solution on the leaves, and rubbing the
leaf surface with a glass rod. This resulted in the formation of rather
small, superficial wounds. The authors observed the tumors first as small
chlorotic outgrowths projecting above the leaf surface. Later the leaf
blade lost its color while the tumors became green. A microscopic study
of tumor development revealed that, as a result of the Carborundum
treatment, a number of epidermal cells had died. Cells of the palisade
parenchyma directly under these divided, and this stimulus spread to the
spongy parenchyma. The minor vascular elements associated with the
developing tumors enlarged and became distorted. Small groups of xylem
cells were found without any connection with the normal vascular
system. The well-developed tumors contained small, heavily stained cells,
disorganized tracheids and, outside the smaller cells, a number of
enlarged cells.
3. Comparison of Wound and Crown Gall Tissue
Only in a few recent studies have the wounded and the crown gall
tissues been compared in the same plant (Bopp and Leppla, 1964;
Lippincott and Heberlein, 1965; Lipetz, 1966). Otherwise, the comparison
between these two tissues can only be based on their general characteristics.
It is interesting that the crown gall development is inhibited in the
monocots, which show none or a weak reaction to wounding, as well as
in the meristematic tissues of the stem and the root tips of dicots, which
show a remarkably strong regenerative power. It could be speculated
that the lack of reactivity in the monocots is correlated with the lack of
ability to continued cell division in their differentiated tissues. However,
some monocots do react to wounding and at least in these plants the
prerequisites for conditioning might be expected to exist. Restudy of the
wound and the crown gall reactions in certain selected monocots might
yield interesting results. In this connection, the question of the reactivity of different cell types in the dicots is of importance. Certain cell
types are reactive, whereas others react slowly, or not at all, to wounding.
The same phenomenon has been described repeatedly in studies dealing
with crown gall. However, it is not certain that the cells react similarly
to both agents. The report of Bopp and Leppla (1964) that the pith of
the Kalanchoe stem proliferates vigorously after wounding but does not
take part in the tumor formation, is a good example of this.