Cytoskeletal and Vacuolar Dynamics During Plant Cell Division 133
Fig. 2Actin microfilament (MF) dynamics during cell cycle progression from S phase to
telophase in tobacco BY-GF cells. MFs are visualized by stable expression of GFP-fimbrin
ABD2 fusion proteins in tobacco BY-2 cells. In S phase, the MFs extend radially from
the nuclear surface to the cell periphery. In G2 phase, transversely oriented cortical MFs
form a band-like structure at the center of the cell. In metaphase, the cortical MF band
in the G2 phase separates to form two bands at the cell cortex, which are designated
as the MFTP (microfilament twin peaks). In telophase, the MFs co-localize with the MT
phragmoplast. Thescale barsrepresent 10 μm
a structure corresponding to the ADZ in mitosis. As measurements of fluores-
cent intensities of the cell cortex indicated an MF distribution that resembled
two peaks, the structure was referred to as “MF twin peaks” (MFTP, Sano
et al. 2005). Transition of the MF band to the MFTP may occur by a gradient of
MF polymerization/depolymerization activity in this region. Time-sequential
observations clearly indicated the formation of the cell plate exactly within
the valley between the MFTP at cytokinesis (Sano et al. 2005), corroborating
the role of the MFTP/ADZ suggested before.
In addition to clarifying MF dynamics during cell division, studies using
the tobacco BY-GF line clearly revealed localization of the MFs along the cy-
toplasmic strands (Sano et al. 2005); a feature not previously recognized by
immuno-fluorescence microscopy because of disruption of the integrity of
membrane structures by fixation. Visualization of the vacuolar membrane
(VM) by vital VM staining with FM4-64 in living tobacco BY-GF cells also
demonstrated co-localization of MF structures and the vacuolar membrane
(Higaki et al. 2006). As treatment with the actin polymerization inhibitor,
bistheonellide A, disrupted the cytoplasmic strands and inhibited the reorga-
nization of this structure at the early G1 phase, MFs have been implicated in