LOCALIZATION
IN THE DEVELOPING
FUCUS
EGG
AND THE GENERAL
ROLE OF LOCALIZING
CURRENTS
LIONEL F. JAFFE
Biology Department, Purdue University, Lafayette,
Indiana
I. Introduction
295
II. Factors of Polarization in the Fucus Egg
300
A. Early Events
300
B. Chemical Gradients
304
C. Electrical Currents
314
III. Localizing Electrical Currents in Other Systems
321
A. Self-generated Currents
321
B. Control of Cell Polarity by Applied Fields
324
IV. Summary
325
References
326
I. Introduction
All animal and most plant eggs are formed by unequal divisions and
have a more or less visible axis built in. By contrast, the eggs of the
common rock weed, Fucus are formed by equal divisions and show no
visible axis (Fig. 1).
These eggs are then shed into the sea and are soon fertilized by a
minute sperm in typical animal fashion. Amidst the swirling waters of
the intertidal zone, and competing with multitudes of others like itself,
each egg seeks a start upon the slimy and thickly populated rocks of its
narrow habitat.
Every detail of early development seems adapted to the urgent first
task of attachment: the eggs are very dense, sinking at a centimeter per
minute. [This density seems to be produced by a very high concentration
of relatively dense, carbohydrate- and tannin-bearing inclusions (Fig.
2).] Quickly after fertilization, the hitherto naked cells secrete a glue
that sticks them tenaciously to virtually any substratum from granite to
Teflon. Their next act is one of overt differentiation. A process of tip
growth begins at one point and generates a sticky protuberance or
rhizoidal region. The embryo then cleaves into a rhizoid cell at the basal
or attachment pole as distinct from a thallus cell at the apical pole
(Fig. 3). This holdfast branches and serves to further anchor the embryo
in the surf.
295