THE ACTIN CYTOSKELETON OF THE LIVERWORT RICCIA-FLUITANS - EFFECTS OF CYTOCHALASIN-B AND ALUMINUM IONS ON RHIZOID TIP GROWTH

Rhodamine phalloidin staining of unfixed gametophytes of the liverwort Riccia fluitans reveals the presence of cortical cables of actin in the rhizoids and undulating bundles in the thallus cells. In both cell types the microfilament arrays are disrupted by cytochalasin B which also causes, in the rhizoids, distorted tip growth, a reduction in the volume of the cytoplasmic cap and forward movement of the nucleus. Actin thus appears to have essential roles in both tip growth and nuclear positioning. Aluminium ions, but not calcium ions, cause similar changes in the actin networks and rhizoid morphology to those induced by cytochalasin B. In the presence of aluminium and high levels of calcium the rhizoid plastids retain chlorophyll. Colocalization of the plastids with actin following aluminium treatments suggests a role for microfilaments in organelle anchorage.