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 t he rhizoids and undulating bundles in the thallus cells. In both cell types the microfilament arrays are disrupted by cytochalasin B which a lso causes, in the rhizoids, distorted tip growth, a reduction in the volume of the cytoplasmic cap and forward movement of the nucleus. Act in thus appears to have essential roles in both tip growth and nuclear positioning. Aluminium ions, but not calcium ions, cause similar chan ges in the actin networks and rhizoid morphology to those induced by c ytochalasin B. In the presence of aluminium and high levels of calcium the rhizoid plastids retain chlorophyll. Colocalization of the plasti ds with actin following aluminium treatments suggests a role for micro filaments in organelle anchorage.