Xyloglucan hydrogen-bonds to cellulose and has been proposed to form load-bearing cross-links between adjacent microfibrils in the primary cell walls of plant cells. Such cross-links may regulate wall extensibility and allow control of cell expansion. Changes in relative molecular mass (M<SUB>r</SUB>) of xyloglucan have been correlated with wall extensibility in several studies. Endotransglycosylation of xyloglucan may cut and reform cross-links, enabling limited cell expansion through temporary loosening of the cell wall. An enzyme capable of catalysing such a reaction, xyloglucan endotransglycosylase (XET), has been reported previously. A pulse-chase radiolabelling approach was used to follow the changes in M<SUB>r</SUB> of a pool of radiolabelled wall-bound xyloglucan in the cell walls of suspension-cultured rose cells as the cells aged. This was done in rapidly-expanding cells and in slowly-expanding cells to study the effects of expansion rate on xyloglucan M<SUB>r</SUB>. Radiolabelled xyloglucan extracted from the cell walls of rapidly-expanding cultures had a M<SUB>r</SUB> consistently ~80000 lower than radiolabelled xyloglucan extracted from slowly-expanding cells. The relationship between xyloglucan M<SUB>r</SUB> and expansion rate is discussed. The radiolabelled xyloglucan in the cell wall extracts of both cultures decreased in M<SUB>r</SUB> by ~40000 during the 7-day observation period, with 20-30% of the radiolabelled xyloglucan being lost from the cell wall. A similar amount of radiolabelled xyloglucan, with a mean M<SUB>r</SUB> of ~39000, accumulated in the culture medium at the same time as the loss from the cell wall. This observation is proposed to be due to trimming of loose (<I>i.e.</I> not directly bound to microfibrils) sections of wall-bound xyloglucan from the cell wall and subsequent sloughing into the culture medium. The possible effects of trimming of xyloglucan on the extensibility of the cell wall are discussed. Protoplasts isolated from suspension-cultured rose cells were used to determine the M<SUB>r</SUB> of newly-secreted xyloglucan.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:662870 |
| Date | January 1996 |
| Creators | Thompson, James |
| Publisher | University of Edinburgh |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | http://hdl.handle.net/1842/13110 |
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