184 Y.-R.J.Lee·B.Liu
3.3
Kinesins as Motors of Vesicle Transport for Cell Plate Assembly
One of the most conspicuous phenomena in plant cytokinesis is the for-
mation of the cell plate. As soon as the phragmoplast microtubule array
is established, along microtubules vesicles are bound towards the division
site (Fig. 6). In samples prepared by rapid freezing and freeze substitution
such as the one shown in Fig. 6, there is a space between the vesicle and
the microtubule, suggesting that they are connected by a linker. A motor-
like structure has also been shown on vesicles in the phragmoplast in an
electron microscopic/tomographic study (Otegui et al. 2001). The orienta-
tion of the phragmoplast microtubules indicates that Golgi-derived vesicles
are transported by plus end-directed kinesin(s) towards the plus end of these
microtubules. Consequently, the fusion of these vesicles gives rise to a tubulo-
Fig. 6 Microtubules and vesicles in the phragmoplast. AnA. thalianacell was pro-
cessed for electron microscopic examination after being fixed by rapid freezing and freeze
substitution.Arrowheadspoint at microtubules, andarrowsat vesicles bound to micro-
tubules.Asteriskpoints at tubulo-vesicular network, formed by vesicle fusion, in the
middle area of the phragmoplast. Thescale barrepresents0.5μm