THE ORGANIZATION OF F-ACTIN IN ROOT-TIP CELLS OF ADIANTUM-CAPILLUS-VENERIS THROUGHOUT THE CELL-CYCLE - A DOUBLE LABEL FLUORESCENCE MICROSCOPY STUDY

The patterns of F-actin in relation to microtubule (Mt) organization in dividing root tip cells of Adiantum capillus veneris were studied with rhodamine-phalloidin (RP) labelling and tubulin immunofluorescence. Interphase cells display a well organized network of cortical/subcortical, endoplasmic and perinuclear actin filaments (AFs), not particularly related to the interphase Mt arrays. The cortical AFs seem to persist during the cell cycle while the large subcortical AF bundles disappear by preprophase/prophase and reappear after cytokinesis is completed. In some but not all of the preprophase cells the cortical AFs tend to form a band (AF-PPB) coincident with the preprophase band of Mts (Mt-PPB). In metaphase and anaphase cells AFs are localized in the cell cortex, around the spindle and inside it coincidently with kinetochore Mt bundles. During cytokinesis AFs are consistently found in the phragmoplast. In oryzalin treated cells neither Mt-PPBs, spindles and phragmoplasts exist, nor such F-actin structures can be observed. In cells recovering from oryzalin, AF-PPBs, "AF kinetochore bundles" and "AF phragmoplasts" reform. They show the same pattern with the reinstating respective Mt arrays. In contrast, in cells treated with cytochalasin B (CB), AFs disappear but all categories of Mt arrays form normally. These observations show that F-actin organization in root tip cells of A. capillus veneris differs from that of root tip cells of flowering plants examined so far. In addition, Mts seem to be crucial for F-actin organization as far as it concerns the PPB, the mitotic spindle, and the phragmoplast.