Plant Cell Monogr (9)
D.P.S. Verma and Z. Hong: Cell Division Control in Plants
DOI 10.1007/7089_2007_121/Published online: 18 August 2007
©Springer-Verlag Berlin Heidelberg 2007
Division Plane Orientation in Plant Cells
Amanda J. Wright · Laurie G. Smith ()
Section of Cell and Developmental Biology, University of California, San Diego,
9500 Gilman Dr., La Jolla, CA 92093, USA
[email protected]
AbstractThis review discusses current knowledge on division plane determination in
plant cells and how division within this plane is executed during cytokinesis. Plants cells
are unusual among eukaryotes in that their planes of division are established prior to the
onset of mitosis. Factors that contribute to the initial selection of the division plane in-
clude extra-cellular signals, cell geometry and polarity, and nuclear position. During the
G2 phase of the cell cycle, the formation of the preprophase band (PPB), a cortical assem-
bly of microtubules and microfilaments, signals the future location of the division plane.
Factors important for PPB formation and maturation include the actin cytoskeleton,
changes in microtubule dynamics, and protein dephosphorylation. Prior to its disassem-
bly at prometaphase, the PPB functions in more than one way to determine subsequent
placement of the new cell wall. First, the PPB influences the initial orientation of the spin-
dle, which facilitates subsequent cell wall formation within the division plane. Second,
the PPB is thought to direct the formation of a cortical division site that persists after
PPB breakdown and interacts during cytokinesis with the expanding phragmoplast, a cy-
toskeletal assembly that directs the deposition of the partitioning cell wall. Both negative
and positive cortical markers are implicated in maintaining the memory of the former
PPB site throughout mitosis and cytokinesis.
1
Introduction
Plants are sessile organisms composed of non-motile cells locked into pos-
ition by rigid cell walls. Plants grow by a combination of cell elongation and
cell division with no cell migration, making a cell’s initial position relative to
that of its neighbors difficult to adjust. Consequently, proper orientation of
new cell walls during cell division is key to ensuring robust plant form and
function. In contrast to animal cells, where cytokinesis is achieved via con-
traction of the plasma membrane between daughter nuclei (cleavage), plant
cells divide by building a new cell wall between the daughter cells. Thus, it is
perhaps not surprising that the mechanisms used by plant cells to orient their
division planes also appear to be different from those of animal cells, where
the division plane is determined by spindle position. In somatic plant cells,
the division plane is established in the cell cortex prior to mitosis, and the
new cell wall is inserted at this site upon completion of cytokinesis.
Initial establishment of the division plane is marked by a cytoskeletal
structure unique to plant cells called the preprophase band (PPB), which ap-