|Title||From Golgi body movement to cellulose microfibril alignment|
|Source||Wageningen University. Promotor(en): Anne Mie Emons, co-promotor(en): Tijs Ketelaar. - S.l. : s.n. - ISBN 9789461733030 - 122|
Laboratory of Cell Biology
|Publication type||Dissertation, internally prepared|
|Keyword(s)||plantencelbiologie - golgiapparaat - organellen - cellulose - cellen - celwanden - microtubuli - arabidopsis thaliana - plant cell biology - golgi apparatus - organelles - cellulose - cells - cell walls - microtubules - arabidopsis thaliana|
|Categories||Plant Cell Biology|
Chapter 1 is an introduction into cellulose deposition and an outline of this thesis.
In chapter 2 the movement and distribution of Golgi bodies is studied in the cortex of cells of different growth stages, early elongation zone compared to late elongation zone, in relation to the configuration of the actin cytoskeleton. Golgi bodies in the cortex of cells in the early elongation zone, where growth accelerates to rapid growth, show slow random oriented movement, called wiggling. In the cortex of cells in the late elongation zone, where cell elongation ceases, they also show a second kind of motility, fast directed movement with velocities of up to 7 µm.s-1, like in cytoplasmic strands in the same cells. The cortical areas where Golgi body movement is slow and random co-localize with fine F-actin, a configuration of single or thin bundles of filaments. On the other hand, areas where Golgi body movement is fast and directed co-localize with thick actin filament bundles. When Golgi bodies enter an area with a different actin cytoskeleton configuration they change their type of motility concomitantly. We conclude that Golgi body dynamics correlate with the actin cytoskeleton organization.
CESA complexes are known to run in rows along CMTs in Arabidopsis hypocotyl cells. In chapter 3 we studied the orientation, density, alignment and movement of CMTs and CESA complexes using immunocytochemistry and live cell imaging. Furthermore we studied the orientation and density of the product of the CESA complexes, the CMFs, in the innermost wall layer with Field Emission Scanning Electron Microscopy (FESEM). The CMTs, the tracks of CESA complexes and the innermost CMFs lay in the same orientation, approximately transverse to the elongation axis in both the inner and outer periclinal cell face in the elongation zone and root hair zone, where cell elongation ceases. CESA complexes predominantly move in rows along CMTs in both directions. While the CMFs form a uniform cell wall layer, CESA complexes run one after the other along CMTs that are wider spread from each other than the CMFs and only few CESA complexes move in between the CMTs. To understand how CESA complexes can produce a uniform layer of CMFs, instead of local CMF thickenings, we studied whether the CMTs change position during CMF production. Time lapse movies of CMTs show that CMTs reposition over time, so that CESA complexes produce an even CMF layer. In this way we can understand how the density of CMFs in the nascent cell wall can be higher than that of the CMTs and the moving rows of CMFs in the plasma membrane. CMFs are deposited consecutively next to earlier deposited ones in the same orientation.
In chapter 4 we used several different electron microscopy techniques to visualize CMF texture: transmission Electron Microscopy (TEM) of ultrathin sections after mild or complete matrix extraction, TEM of surface preparations and FESEM of surface preparations. We used root hairs of three different species; Arabidopsis thaliana, Medicago truncatula and Vicia sativa. We compare and discuss the results of the techniques for the capacity to measure orientation, density, length and width of the CMFs. In ultrathin sections and surface preparations we observed that the three species studied have root hairs with an axial/helical wall texture. Surface preparations are best suitable for density and orientation measurements of CMFs within the most inner cell wall layer. Ultrathin sections showed that the thickness of CMFs in Arabidopsis is approximately 3 nm. which indicates that these CMFs are produced by single CESA complexes.
Chapter 5 is a general discussion of our work in relation to the field. It describes the role of the actin cytoskeleton , Golgi body motility and CMTs in the deposition of an organized texture of CMFs.