LOCALIZATION IN THE DEVELOPING FUCUS EGG
307
to indicate substantial polarization by as little as 2 X 10~
5 M IAA. Moreover, Avena tests of chloroform extracts of unfertilized eggs indicate the
presence therein of about 10"
6 M IAA (du Buy and Olson, 1937). These
authors, therefore, suggested rhizin to be IAA.
About 10 years ago, I began to reinvestigate the group effects. I was
first surprised to find that, in groups of 2000 eggs, peripheral eggs showed
a strong tendency to germinate inwardly even in and well above the pH
range that elicits a negative effect in pairs (Fig. 10). In this case, it is
plain that high cell concentrations are favoring the positive group effect
through a means other than a reduction in the average pH. How?
One explanation would depend upon the assumptions that antirhizin is
stable, but rhizin decays rapidly near eggs: It is well known that when
organisms respond to a difference of stimuli, their response generally depends upon the relative rather than the absolute difference. Indeed, in the
available, quantitatively investigated cases of cell polarization by imposed gradients—of light (Jaffe and Etzold, 1962), of hydrogen ion
(Bentrup et al., 1967), and of an unidentified cell-secreted stimulator
(Jaffe, 1966b)—in all of these cases, percent orientation approximately
equals percent imposed gradient. Now it is easily shown that in the
steady state the relative diffusion gradients outside of a source of a
stable substance are simply given by 1/r, where r is the distance, in
responding cell diameters, to the source's center. This distance, from the
responding cells at the edge of each 2000-egg group to its center, was 1020 times that from each egg in a pair to this group's center. The relative
gradients of a stable substance near the large groups should be correspondingly reduced; but for a sufficiently unstable substance the peripheral test eggs would receive material from only a few nearest cells and
such mass reduction or drowning of the relative gradients would not occur.
This conjecture was directly tested and confirmed by measuring the
effects of gradients of egg water, i.e., medium exposed to developing eggs.
Test eggs showed a strong tendency to germinate away from this medium
at both high and low pH's (Table III). This is what was to be expected
if, in fact, antirhizin persisted while rhizin decayed and disappeared in
the supernatant. The effects of uniformly applied egg water were likewise
consistent with this inference. Moreover, in egg water (at pH 8.2), egg
pairs showed a greatly increased tendency to grow toward each other as
well as toward the glass substratum (Table IV). Presumably, antirhizin
in the added egg water had drowned out the test eggs' gradients of this
substance and, thus, shifted the balance toward the unswamped rhizin
gradients.
307
to indicate substantial polarization by as little as 2 X 10~
5 M IAA. Moreover, Avena tests of chloroform extracts of unfertilized eggs indicate the
presence therein of about 10"
6 M IAA (du Buy and Olson, 1937). These
authors, therefore, suggested rhizin to be IAA.
About 10 years ago, I began to reinvestigate the group effects. I was
first surprised to find that, in groups of 2000 eggs, peripheral eggs showed
a strong tendency to germinate inwardly even in and well above the pH
range that elicits a negative effect in pairs (Fig. 10). In this case, it is
plain that high cell concentrations are favoring the positive group effect
through a means other than a reduction in the average pH. How?
One explanation would depend upon the assumptions that antirhizin is
stable, but rhizin decays rapidly near eggs: It is well known that when
organisms respond to a difference of stimuli, their response generally depends upon the relative rather than the absolute difference. Indeed, in the
available, quantitatively investigated cases of cell polarization by imposed gradients—of light (Jaffe and Etzold, 1962), of hydrogen ion
(Bentrup et al., 1967), and of an unidentified cell-secreted stimulator
(Jaffe, 1966b)—in all of these cases, percent orientation approximately
equals percent imposed gradient. Now it is easily shown that in the
steady state the relative diffusion gradients outside of a source of a
stable substance are simply given by 1/r, where r is the distance, in
responding cell diameters, to the source's center. This distance, from the
responding cells at the edge of each 2000-egg group to its center, was 1020 times that from each egg in a pair to this group's center. The relative
gradients of a stable substance near the large groups should be correspondingly reduced; but for a sufficiently unstable substance the peripheral test eggs would receive material from only a few nearest cells and
such mass reduction or drowning of the relative gradients would not occur.
This conjecture was directly tested and confirmed by measuring the
effects of gradients of egg water, i.e., medium exposed to developing eggs.
Test eggs showed a strong tendency to germinate away from this medium
at both high and low pH's (Table III). This is what was to be expected
if, in fact, antirhizin persisted while rhizin decayed and disappeared in
the supernatant. The effects of uniformly applied egg water were likewise
consistent with this inference. Moreover, in egg water (at pH 8.2), egg
pairs showed a greatly increased tendency to grow toward each other as
well as toward the glass substratum (Table IV). Presumably, antirhizin
in the added egg water had drowned out the test eggs' gradients of this
substance and, thus, shifted the balance toward the unswamped rhizin
gradients.