DIFFERENT EXTENT OF F-ACTIN BUNDLING IN WALLED CELLS AND IN PROTOPLASTS OF MOUGEOTIA-SCALARIS

F-actin was localized in Mougeotia interphase cells by rhodamine phalloidin (RLP) using an extended, formaldehyde-based fixation protocol, which included a minimal concentration of 0.05% (v/v) glutardialdehyde and stabilization of the calcium-binding vesicles by presaturation with neutral red. Staining revealed a low level of RLP-fluorescence throughout the cytoplasm. An enhanced level of RLP-fluorescence was found around the nucleus and in mostly two parallel fringes along each longitudinal chloroplast edge; also close to the chloroplast edge, quite regularly spaced patches of RLP-fluorescence were seen possibly associated with dictyosomes. The diffuse staining indicates lack of F-actin bundles in Mougeotia filamentous cells, in contrast to Spirogyra interphase cells or Mougeotia protoplasts. The observations upon staining with RLP confirm previous findings by electron microscopy and indicate seemingly single actin filaments throughout the entire Mougeotia filamentous cell. Thus, a special F-actin organization is evident here which for the chloroplast movement is in support of the hypothesis of pigment regulated plasmalemma anchorage sites to actin filaments. © 1990 Springer-Verlag.