206
F.
C. STEWARD AND
Η. Y. MOHAN RAM
require the prior addition of indoleacetic acid, and, in fact, many of the
very active fractions isolated therefrom do not profit from the additional
presence of indoleacetic acid. There can be no question that the substance called 'kinetin' is a cell division promoting substance under the
conditions described by Miller et al., and also under the conditions of
the carrot assay, provided indoleacetic acid is present. There can also be
no doubt that the amount of cell division so produced is not as large as
that which can be produced by some of the active extracts mentioned,
or even by certain other now known chemical substances. Indeed, a
recent survey of a number of 6-substituted purines, as communicated
from this laboratory by Shantz to the Growth Symposium held at
Yonkers in 1959, shows that some other such synthetic substances
[6-benzylaminopurine, 6-(o-methylbenzyl)aminopurine, 6-(^-methylbenzyl)aminopurine] will considerably exceed kinetin as the agents of
growth induction in presence of indoleacetic acid (IAA) as tested by the
carrot assay method. Indeed, some of these substances at suitable
concentrations, in appropriate association with indoleacetic acid, rival
the effects otherwise due to whole coconut milk. Thus there is represented
another class of growth-inducing substances that act by promoting cell
division, and these seem to bear little resemblance to other similarly
active substances. A major contribution, however, from Skoog's
laboratory is the evidence of the role that substances like kinetin may
play in conjunction with others in the control of differentiation; these
effects will be discussed later. Although it has no obvious relation to the
6-substituted aminopurines, the substance 2-benzothiazolyloxyacetic
acid has been found to be very effective in stimulating division in
certain tissue cultures, even in the absence of IAA, as noted from this
laboratory (Steward and Shantz, 1956).
6. Cell Division in Crown Gall Tissue
The chemical stimulus to cell division, discussed above, resembles
that which causes crown gall tumour formation (cf. Fig. 2(h)), with the
exception that, once embarked upon this course, the cells of the tumour
become autotrophic for the stimuli in question. Braun, of the Rockefeller
Institute at New York, has given much attention to this long standing
problem. Reference may be made to the following papers (Braun, 1954,
1958,1959,1960).The salient point relevant to this discussion is,however,
as follows. Cells already exhibiting a wound-healing type of response
become prepared for, or become receptive to, the growth induction
stimulus to cell division en route to the formation of a tumour. Cells in
this modified or receptive state have been induced to grow in culture by
suitable combinations of growth substances in such a way that they
resemble the growth in culture of the crown gall tumour tissue. The
F.
C. STEWARD AND
Η. Y. MOHAN RAM
require the prior addition of indoleacetic acid, and, in fact, many of the
very active fractions isolated therefrom do not profit from the additional
presence of indoleacetic acid. There can be no question that the substance called 'kinetin' is a cell division promoting substance under the
conditions described by Miller et al., and also under the conditions of
the carrot assay, provided indoleacetic acid is present. There can also be
no doubt that the amount of cell division so produced is not as large as
that which can be produced by some of the active extracts mentioned,
or even by certain other now known chemical substances. Indeed, a
recent survey of a number of 6-substituted purines, as communicated
from this laboratory by Shantz to the Growth Symposium held at
Yonkers in 1959, shows that some other such synthetic substances
[6-benzylaminopurine, 6-(o-methylbenzyl)aminopurine, 6-(^-methylbenzyl)aminopurine] will considerably exceed kinetin as the agents of
growth induction in presence of indoleacetic acid (IAA) as tested by the
carrot assay method. Indeed, some of these substances at suitable
concentrations, in appropriate association with indoleacetic acid, rival
the effects otherwise due to whole coconut milk. Thus there is represented
another class of growth-inducing substances that act by promoting cell
division, and these seem to bear little resemblance to other similarly
active substances. A major contribution, however, from Skoog's
laboratory is the evidence of the role that substances like kinetin may
play in conjunction with others in the control of differentiation; these
effects will be discussed later. Although it has no obvious relation to the
6-substituted aminopurines, the substance 2-benzothiazolyloxyacetic
acid has been found to be very effective in stimulating division in
certain tissue cultures, even in the absence of IAA, as noted from this
laboratory (Steward and Shantz, 1956).
6. Cell Division in Crown Gall Tissue
The chemical stimulus to cell division, discussed above, resembles
that which causes crown gall tumour formation (cf. Fig. 2(h)), with the
exception that, once embarked upon this course, the cells of the tumour
become autotrophic for the stimuli in question. Braun, of the Rockefeller
Institute at New York, has given much attention to this long standing
problem. Reference may be made to the following papers (Braun, 1954,
1958,1959,1960).The salient point relevant to this discussion is,however,
as follows. Cells already exhibiting a wound-healing type of response
become prepared for, or become receptive to, the growth induction
stimulus to cell division en route to the formation of a tumour. Cells in
this modified or receptive state have been induced to grow in culture by
suitable combinations of growth substances in such a way that they
resemble the growth in culture of the crown gall tumour tissue. The