72
SIRKKA KUPILA-AHVENNIEMI AND EEVA THERMAN
unspecified cytoplasmic particles. The third hypothesis places the origin
of the tumor on the level of various differentiation and dedifferentiation
phenomena.
A number of observations virtually exclude a gene or a chromosome
mutation, but are compatible with the other two possibilities. To sum up:
1. Braun's (1951, 1959) experiments have shown that cells from a
teratoma-type crown gall are able to revert back to normal, when forced
into rapid division by repeated grafting to the top of a host stem. A
possible selection for normal cells in the teratoma tissue is excluded by
the precaution of starting the tumor from a single cell.
2. When the necessary conditions are realized—virulent bacteria,
suitable host, wound at the right stage of healing—practically all the
inoculated sites develop tumors. In addition, all the cells around a
wound—diploid as well as polyploid—seem to undergo a conversion. As
a result, the larger the wound, the larger grows the tumor.
3. Different degrees of change can be achieved by varying either the
bacterial strain, the timing of the conditioning, or the length of the
transformation period (cf. Braun, 1954a,b).
4. The change expresses itself through an activation of normal growth
substance systems. Braun's (1958) experiments have shown that whereas
normal tissue in culture is completely unable to grow on White's basic
medium, a fast growing crown gall tumor has this ability. To achieve
the same growth as the rapid tumor on this medium, the moderate tumor
needs, in addition, glutamine, inositol, and naphthalene acetic acid; the
slow tumor needs these plus asparagine and cytidylic and guanylic acid;
and the normal tissue needs all these plus 6-furfurylaminopurine.
Evidence against the idea that the bacteria themselves in some
modified form, for instance as spheroplasts, are the causative agent, has
been presented by Beardsley et al. (1966). They found that permanent
spheroplasts, produced by D-methionine treatment, do not incite tumors
in Kalanchoe
or the Boston daisy, and that the efficiency of tumor
induction in the Kalanchoe stem is lower for glycine-induced revertible
spheroplasts than for normal rod forms.
Caspari (1948) and Jinks (1964) have reviewed the evidence on cytoplasmic inheritance. Extranuclear inheritance can be attributed to a
series of particles ranging from true viruses and episomes, through viruslike particles, such as kappa and sigma, to true plasmatic units, the last
of which have been called plasmagenes. A distinction between these
groups is often difficult, if not impossible (cf. Darlington, 1948).
SIRKKA KUPILA-AHVENNIEMI AND EEVA THERMAN
unspecified cytoplasmic particles. The third hypothesis places the origin
of the tumor on the level of various differentiation and dedifferentiation
phenomena.
A number of observations virtually exclude a gene or a chromosome
mutation, but are compatible with the other two possibilities. To sum up:
1. Braun's (1951, 1959) experiments have shown that cells from a
teratoma-type crown gall are able to revert back to normal, when forced
into rapid division by repeated grafting to the top of a host stem. A
possible selection for normal cells in the teratoma tissue is excluded by
the precaution of starting the tumor from a single cell.
2. When the necessary conditions are realized—virulent bacteria,
suitable host, wound at the right stage of healing—practically all the
inoculated sites develop tumors. In addition, all the cells around a
wound—diploid as well as polyploid—seem to undergo a conversion. As
a result, the larger the wound, the larger grows the tumor.
3. Different degrees of change can be achieved by varying either the
bacterial strain, the timing of the conditioning, or the length of the
transformation period (cf. Braun, 1954a,b).
4. The change expresses itself through an activation of normal growth
substance systems. Braun's (1958) experiments have shown that whereas
normal tissue in culture is completely unable to grow on White's basic
medium, a fast growing crown gall tumor has this ability. To achieve
the same growth as the rapid tumor on this medium, the moderate tumor
needs, in addition, glutamine, inositol, and naphthalene acetic acid; the
slow tumor needs these plus asparagine and cytidylic and guanylic acid;
and the normal tissue needs all these plus 6-furfurylaminopurine.
Evidence against the idea that the bacteria themselves in some
modified form, for instance as spheroplasts, are the causative agent, has
been presented by Beardsley et al. (1966). They found that permanent
spheroplasts, produced by D-methionine treatment, do not incite tumors
in Kalanchoe
or the Boston daisy, and that the efficiency of tumor
induction in the Kalanchoe stem is lower for glycine-induced revertible
spheroplasts than for normal rod forms.
Caspari (1948) and Jinks (1964) have reviewed the evidence on cytoplasmic inheritance. Extranuclear inheritance can be attributed to a
series of particles ranging from true viruses and episomes, through viruslike particles, such as kappa and sigma, to true plasmatic units, the last
of which have been called plasmagenes. A distinction between these
groups is often difficult, if not impossible (cf. Darlington, 1948).