Investigation of the earliest events in embryonic polarization in plants have focused on two genera of closely related brown algae, Fucus and Pelvetia. Current working hypotheses postulate that during polarization ion channels in the plasma membrane migrate to one end of the egg. This asymmetry gives rise to net influx in the region of channel accumulation and net efflux from the other end. Thus, an ionic current flows through the egg and denotes formation of the developmental axis. As a consequence of the current, cytoplasmic voltage and ionic gradients are established and these are thought to regulate regional differentiation within the egg. One major aspect of this attractive model that has yet to be scrutinized is whether a physical reorganization of plasma membrane components (e.g.ion channels) takes place as the axis is established. Dr. Kropf has recently shown that Fucus protoplasts made from young zygotes can be polarized with unidirectional light. This provides direct access to the plasma membrane during axis establishment. He will examine rearrangements of membrane receptors on the surface of protoplasts undergoing polarization and investigate ionic currents generated by the membrane asymmetries in Fucus zygotes and in photopolarized protoplasts. The ultimate goal is to monitor the spatial distributions of ionic currents, plasma membrane receptors and F-actin in single cells as they establish an axis. %%% The establishment of the axis (i.e. which end is which) of an organism early in development is a fundamental first step in the pattern formation of that organism. This event has been hard to analyze in plants. Dr. Kropf is studying this process in the brown algae because of the experimental advantages it presents relative to many other plants.
