MICROFILAMENT DISTRIBUTION IN PROTONEMATA OF THE MOSS CERATODON

Microfilaments were visualized in dark-grown protonemata of the moss C eratodon to assess their possible role in tip growth and gravitropism. The relative effectiveness of rhodamine phalloidin (with or without M BS) and of immunofluorescence (using the C4 antibody) was evaluated fo r actin localization in the same cell type. Using immunofluorescence, microfilaments were primarily in an axial orientation within the apica l cell. However, a more complex network of microfilaments was observed using rhodamine phalloidin after MBS pretreatment, especially when vi ewed by confocal laser scanning microscopy. This method revealed a ric h three dimensional network of fine microfilaments throughout the apic al cell, including the extreme apex. Although there were numerous inte rnal microfilaments, peripheral microfilaments were more abundant. No major redistribution of microfilaments was detected after gravistimula tion. The combination of MBS, rhodamine phalloidin, and confocal laser scanning microscopy preserves and reveals microfilaments remarkably w ell and documents perhaps the most extensive F-actin network visualize d to date in any tip-growing cell.