Research Interests:
My area of interest is plant cell biology, especially the
biosynthesis and secretion of the plant cell wall.
The study of the extracellular matrix in plants presents
special challenges for cell biologists due to the tight
association of the wall with the plasma membrane and the
plants' turgor-driven mode of growth. The cell wall limits
the reagents and probes that can be applied to the plant
cell and removal of the cell wall requires altering the
normal osmotic environment of the cell. For these reasons,
I use specialized freezing techniques (cryofixation) such
as high pressure freezing, which can immobilize cell water
intact and allow detailed electron microscopic examination
of the cell.
1. Cytokinesis
In the past, I have studied how dividing plant cells produce
the new cell wall following mitosis. Using cryofixation,
as well as antibody probes, a new view of the developing
cell plate was elucidated in tobacco cells grown in culture.
More recently, we have studied this process in the inner
bark (secondary vascular cambium) of pine and found the
same delicate membrane structures as in tobacco.
TEM of High pressure frozen/Freeze substituted Pine cambium
showing new cell wall forming (cell plate).
Rensing et al. (2002).
2. Xylem development and lignification
Recently my research interests have expanded to focus on
non-polysaccharide components of the cell wall such as lignin
and wax. Lignin is a polymer made up of units called monolignols,
which link together to give plant cell walls strength. The
monolignols must be exported from the cytoplasm to specific
sites in the cell wall. Using developing secondary xylem
(wood) of Pinus contorta var. latifolia (Lodgepole Pine)
as an experimental system, We are exploring how some of
the enzymes of monolignol biosynthesis are arranged in the
cell and what is the cellular mechanism of monolignol export.
Typical cell structures observed in developing xylem from
Pinus contorta var. latifolia. Cells were prepared by cryofixation
and TEM. Both membrane and cytoskeleton structures are preserved
in these cells which are actively secreting the thick secondary
cell wall.
Unusual Golgi structures are characteristic of differentiating
Pinus secondary xylem (wood). Cells were prepared by cryofixation
and TEM. We are presently using cryo-fixation and autoradiography
to study the distribution of phenylpropanoids in these cells.
3. Epicuticular wax secretion in Arabidopsis
cryoSEM of wax on the surface of an Arabidopsis stem.
Wax is an essential feature of aerial portions of plants,
as it limits water loss and protects from environmental
and insect stresses. The epidermal cells of the stem synthesize
and secrete this hydrophobic product. It is not known if
secretion is Golgi-mediated or how the hydrophobic product
is targeted to the extracellular environment. In Arabidopsis
thaliana, mutants have been identified which are impaired
in stem wax productions. Studying these mutants using a
combination of cryofixation/electron microscopy, light microscopy,
gas chromatography, and freeze fracture, is giving us new
insights on the mechanism of wax secretion.
