204
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the 'neutral' fraction and the 'active' fraction of the coconut milk, they
are still subject to further regulatory control by interactions with
stimulators, on the one hand, or inhibitors on the other. However,
2,4-D is but one example of a great many substances which can interact
with coconut milk in a synergistic fashion. Several families of these
substances have been investigated.
It has been possible to show the effects of substitution in the aromatic
nucleus of certain phenoxyacetic acids upon the growth of potato tissue
and to distinguish groupings which promote either cell division or
enlargement. In this family of compounds a substituent in the 2, or
ortho position, tends to promote cell division, whereas a substituent in
the 4, or para position, tends to promote cell enlargement. Thus the
two-four combination (as in 2,4-D) was a particularly suitable one in its
interaction with coconut milk to make the cells of the potato tuber grow
(Steward and Caplin, 1952).
Phenoxy acids with a longer sidechain have an effect that is very
specifically related to their constitution (Steward et al., 1956; Steward
and Shantz, 1959b). Following the ideas of Fawcett et al., (1954) and
Wain and Wightman (1954), from whom these substances were obtained,
it is apparent that substances with sidechains with an even number of
carbon atoms produce molecules which are active in this potato-coconut
milk assay system, whereas compounds with side-chains with an odd
number of carbon atoms are not so active. The interpretation is, again
following Wain and Wightman (1954), that the sidechain is first
degraded by jS-oxidation, removing two carbon atoms simultaneously,
so that the sidechain may be reduced to a substituted acetic acid, which
is effective as a synergist. If the sidechain has an uneven number of
carbon atoms, their removal two at a time cannot result in a substituted
acetic acid, and therefore the substance is inactive.
These results indicate, therefore, the extreme specificity of the relations between molecular structure and the induction of growth; this
is shown not only by the active principles and their direct effects on
growth, but also by the structure of the substances which can act as
synergists. So sensitive are these structural relationships that one set of
substances (α-substituted propionic acids) promotes cell division in the
form of one optical enantiomorph (I) whereas the other (d) actually
functions as a competitive inhibitor (Shantz, Steward, Smith and Wain,
1955).
Thus there is ample opportunity, in the interpretation of normal
growth and development, for the effect of the principles which govern
cell division to be controlled by sensitive chemical means; they may be
stimulated by synergists or suppressed by inhibitors. For example,
hydroxy-Z-proline and certain substances which resemble this molecule
F.
C.
STEWARD
AND
Η.
Y.
MOHAN
RAM
the 'neutral' fraction and the 'active' fraction of the coconut milk, they
are still subject to further regulatory control by interactions with
stimulators, on the one hand, or inhibitors on the other. However,
2,4-D is but one example of a great many substances which can interact
with coconut milk in a synergistic fashion. Several families of these
substances have been investigated.
It has been possible to show the effects of substitution in the aromatic
nucleus of certain phenoxyacetic acids upon the growth of potato tissue
and to distinguish groupings which promote either cell division or
enlargement. In this family of compounds a substituent in the 2, or
ortho position, tends to promote cell division, whereas a substituent in
the 4, or para position, tends to promote cell enlargement. Thus the
two-four combination (as in 2,4-D) was a particularly suitable one in its
interaction with coconut milk to make the cells of the potato tuber grow
(Steward and Caplin, 1952).
Phenoxy acids with a longer sidechain have an effect that is very
specifically related to their constitution (Steward et al., 1956; Steward
and Shantz, 1959b). Following the ideas of Fawcett et al., (1954) and
Wain and Wightman (1954), from whom these substances were obtained,
it is apparent that substances with sidechains with an even number of
carbon atoms produce molecules which are active in this potato-coconut
milk assay system, whereas compounds with side-chains with an odd
number of carbon atoms are not so active. The interpretation is, again
following Wain and Wightman (1954), that the sidechain is first
degraded by jS-oxidation, removing two carbon atoms simultaneously,
so that the sidechain may be reduced to a substituted acetic acid, which
is effective as a synergist. If the sidechain has an uneven number of
carbon atoms, their removal two at a time cannot result in a substituted
acetic acid, and therefore the substance is inactive.
These results indicate, therefore, the extreme specificity of the relations between molecular structure and the induction of growth; this
is shown not only by the active principles and their direct effects on
growth, but also by the structure of the substances which can act as
synergists. So sensitive are these structural relationships that one set of
substances (α-substituted propionic acids) promotes cell division in the
form of one optical enantiomorph (I) whereas the other (d) actually
functions as a competitive inhibitor (Shantz, Steward, Smith and Wain,
1955).
Thus there is ample opportunity, in the interpretation of normal
growth and development, for the effect of the principles which govern
cell division to be controlled by sensitive chemical means; they may be
stimulated by synergists or suppressed by inhibitors. For example,
hydroxy-Z-proline and certain substances which resemble this molecule