202
F. C. STEWARD AND
Η. Y. MOHAN RAM
the constituents of the 'neutral' fraction. When both of these fractions
are present in proper balance, the tissue preferentially utilizes reduced
forms of nitrogen to synthesize its protein and to support the nitrogen
metabolism of the dividing cells.
There is also reason to believe that the other sources (like corn in the
milk stage; the liquid from immature Aesculus fruits) also contain the
chemical equivalents of 'neutral' and 'active' fractions respectively; but
there is no guarantee—in fact there is evidence to the contrary—that
the same substances comprise the corresponding fractions in different
plants. It is significant, however, that the same general categories of
effects reside in morphologically comparable sources.
Even before the synergistic role of the 'neutral' fraction was
appreciated, several active substances had been isolated in minute
amounts from coconut milk (for a recent summary see Steward and
Shantz, 1959b, and references there cited). One of these, the so-called
Compound A (Shantz and Steward, 1952) was finally identified as
1,3-diphenylurea (Shantz and Steward, 1955); this definitely stimulates
cell division in carrot tissue, though it does not approach the effects of
whole coconut milk.
In all of the sources investigated (coconut milk, immature corn,
immature Aesculus fruits) substances belonging to the class of leucoanthocyanins seem to be associated with the growth induction response
in carrot cells. Though these substances are difficult to purify, and defy
synthesis, they can be shown to belong to the class of leuco-anthocyanins.
Chemically uniform products have been obtained and, after hydrolysis,
they yield cyanidin and glucose. It is indeed interesting that leucoanthocyanins can exert this physiological effect, for this may provide
the rationale for the wide distribution of such substances, often in
immature or developing organs or in regions of cambial activity
(Hillis, 1955), and for their later conversion to the inactive coloured
anthocyanins as growth subsides. However, to induce growth, leucoanthocyanins need to be present in the medium at a higher concentration
than the constituents of the so-called 'active' fraction of coconut milk,
though their effect upon cell division is now beyond question. Flowing
from these observations, some fragments of the leuco-anthocyanin
molecule and a number of related phenolic compounds have been tested,
and many of these have some ability to stimulate cell division when
added, in lieu of coconut milk, to the basal medium for carrot explants.
(This was notably true of such substances as a pelargonidin monoglucoside, samples of catechin and epicatechin. Even protocatechuic
acid shows activity.)
However, each of the main sources—coconut milk, corn extract, and
Aesculus extract respectively—seems to yield somewhat different but
F. C. STEWARD AND
Η. Y. MOHAN RAM
the constituents of the 'neutral' fraction. When both of these fractions
are present in proper balance, the tissue preferentially utilizes reduced
forms of nitrogen to synthesize its protein and to support the nitrogen
metabolism of the dividing cells.
There is also reason to believe that the other sources (like corn in the
milk stage; the liquid from immature Aesculus fruits) also contain the
chemical equivalents of 'neutral' and 'active' fractions respectively; but
there is no guarantee—in fact there is evidence to the contrary—that
the same substances comprise the corresponding fractions in different
plants. It is significant, however, that the same general categories of
effects reside in morphologically comparable sources.
Even before the synergistic role of the 'neutral' fraction was
appreciated, several active substances had been isolated in minute
amounts from coconut milk (for a recent summary see Steward and
Shantz, 1959b, and references there cited). One of these, the so-called
Compound A (Shantz and Steward, 1952) was finally identified as
1,3-diphenylurea (Shantz and Steward, 1955); this definitely stimulates
cell division in carrot tissue, though it does not approach the effects of
whole coconut milk.
In all of the sources investigated (coconut milk, immature corn,
immature Aesculus fruits) substances belonging to the class of leucoanthocyanins seem to be associated with the growth induction response
in carrot cells. Though these substances are difficult to purify, and defy
synthesis, they can be shown to belong to the class of leuco-anthocyanins.
Chemically uniform products have been obtained and, after hydrolysis,
they yield cyanidin and glucose. It is indeed interesting that leucoanthocyanins can exert this physiological effect, for this may provide
the rationale for the wide distribution of such substances, often in
immature or developing organs or in regions of cambial activity
(Hillis, 1955), and for their later conversion to the inactive coloured
anthocyanins as growth subsides. However, to induce growth, leucoanthocyanins need to be present in the medium at a higher concentration
than the constituents of the so-called 'active' fraction of coconut milk,
though their effect upon cell division is now beyond question. Flowing
from these observations, some fragments of the leuco-anthocyanin
molecule and a number of related phenolic compounds have been tested,
and many of these have some ability to stimulate cell division when
added, in lieu of coconut milk, to the basal medium for carrot explants.
(This was notably true of such substances as a pelargonidin monoglucoside, samples of catechin and epicatechin. Even protocatechuic
acid shows activity.)
However, each of the main sources—coconut milk, corn extract, and
Aesculus extract respectively—seems to yield somewhat different but