316
LIONEL
F.
JAFFE
each egg of currents
5 which each egg drives through itself from rhizoidal
to thallus end (Figs. 15 and 16). These currents begin just as the eggs
germinate in the case of Fucus furcatus, and a few hours earlier in the
case of Pelvetia fastigiata
(Fig. 17). By the time about 90% of the eggs
have germinated,
0 at least
7 6 X 10"
11 amp is flowing through each of them.
Dividing this by an initial outgrowth's cross-sectional area gives an
initial current density of about 6 /xamp/cm
2
.
Once the eggs' axes are established by light, the current develops
whether or not they are illuminated. The current continues to rise until
the two-to-four cell stage, when it reaches about 9 X 10"
10 amp per
embryo. Subsequently, egg development in the tubes was greatly inhibited
and few cleaved again. During this period of inhibition, the rate of
elongation and the current fell in close parallel.
These transcellular currents were associated with the inherent pattern
of development in each egg rather than the particular environmental
vector, namely unilateral light, used to induce parallel development of
the population. This is shown by the similar development of the current
in light and in darkness (once parallel development has been induced)
and by the close correlation of the current's rise with the population's
germination as well as of its subsequent fall with the slowing of elongation within the confines of the capillary.
An interesting speculation as to the immediate cause of these developmental currents is suggested by several facts. First, one notes that the
potential external to each cell was relatively negative in the region of
expansion. Since plasma membrane potentials in marine cells are always
positive externally, this means that the membrane in the expansion
region is relatively depolarized.
Second, it is found that the tube potentials are quite noisy showing
5
Considered as a flow of positive ions.
c The initial growth stage (IGS).
7
Calculated on the assumption that all of the current moves from pole to pole
and thus traverses the resistance of all of the seawater lateral to each egg. Since
much of it must move in shorter and, hence, less resistive loops, the true current
must have been higher, perhaps 3 times higher.
FIG. 17. Time course of currents flowing through developing eggs of Fucus (above)
and Pelvetia (below). Data from 6 Fucus tubes and 5 Pelvetia ones are pooled. The
time that the Fucus eggs began to germinate, or their rise time, varied from 10 to 14
hours after fertilization in different tubes; hence the Fucus data are plotted with
reference to this time instead of the fertilization time. Fucus data have been published in a different form (Jaffe, 1966a); Pelvetia data have not been published
before.
LIONEL
F.
JAFFE
each egg of currents
5 which each egg drives through itself from rhizoidal
to thallus end (Figs. 15 and 16). These currents begin just as the eggs
germinate in the case of Fucus furcatus, and a few hours earlier in the
case of Pelvetia fastigiata
(Fig. 17). By the time about 90% of the eggs
have germinated,
0 at least
7 6 X 10"
11 amp is flowing through each of them.
Dividing this by an initial outgrowth's cross-sectional area gives an
initial current density of about 6 /xamp/cm
2
.
Once the eggs' axes are established by light, the current develops
whether or not they are illuminated. The current continues to rise until
the two-to-four cell stage, when it reaches about 9 X 10"
10 amp per
embryo. Subsequently, egg development in the tubes was greatly inhibited
and few cleaved again. During this period of inhibition, the rate of
elongation and the current fell in close parallel.
These transcellular currents were associated with the inherent pattern
of development in each egg rather than the particular environmental
vector, namely unilateral light, used to induce parallel development of
the population. This is shown by the similar development of the current
in light and in darkness (once parallel development has been induced)
and by the close correlation of the current's rise with the population's
germination as well as of its subsequent fall with the slowing of elongation within the confines of the capillary.
An interesting speculation as to the immediate cause of these developmental currents is suggested by several facts. First, one notes that the
potential external to each cell was relatively negative in the region of
expansion. Since plasma membrane potentials in marine cells are always
positive externally, this means that the membrane in the expansion
region is relatively depolarized.
Second, it is found that the tube potentials are quite noisy showing
5
Considered as a flow of positive ions.
c The initial growth stage (IGS).
7
Calculated on the assumption that all of the current moves from pole to pole
and thus traverses the resistance of all of the seawater lateral to each egg. Since
much of it must move in shorter and, hence, less resistive loops, the true current
must have been higher, perhaps 3 times higher.
FIG. 17. Time course of currents flowing through developing eggs of Fucus (above)
and Pelvetia (below). Data from 6 Fucus tubes and 5 Pelvetia ones are pooled. The
time that the Fucus eggs began to germinate, or their rise time, varied from 10 to 14
hours after fertilization in different tubes; hence the Fucus data are plotted with
reference to this time instead of the fertilization time. Fucus data have been published in a different form (Jaffe, 1966a); Pelvetia data have not been published
before.