[Uncoupling of morphogenetic processes in Acetabularia mediterranea by P-fluorophenylalanine]

1. Cap-formation of nucleated and enucleated plants of Acetabularia mediterranea was inhibited by 10-50 μg/ml p-fluorophenylalanine almost completely, while the formation of the stalk and whorls as well as protein synthesis is only slightly affected. 2. This selective inhibition of cap-formation by fluorophenylalanine is cancelled by phenylalanine or tyrosine. 3. The inhibition caused by flourophenylalanine is reversible if the plants are transferred into Erdschreiber medium without fluorophenylalanine before cap-formation starts. But the inhibition is largly (nucleated plants) or totally (enucleated plants) irreversible, if the back-transfer takes place after a large part of the control plants has finished cap-formation. 4. Plants which were exposed to fluorophenylalanine a few days before cap-formation is initiated are able to form a small cap, but further growth of the cap is stopped. 5. The following conclusions can be drawn from these results. The activities of the proteins which control stalk-and whorl formation in Acetabularia mediterranea are not influenced by the incorporation of p-fluorophenylalanine. On the other hand one or a few proteins which control cap-formation are inactivated by the incorporation of the fluorine-containing analogue. Therefore cap-formation is controlled by another set of enzymes and structural proteins than stalk-und whorl formation. 6. The synthesis of the proteins which are specific for cap-formation is started a few days before the actuel onset of cap-formation. Synthesis of these specific proteins is also necessary for the further growth of the cap.