Xyloglucan is thought to form cross-links between cellulose microfibrils within the plant cell wall. The hydrolysis of these 'tethers' may be involved in wall loosening, and a control of cell expansion. Transglycosylation reactions between xyloglucan 'tethers' has for some years been suggested as an alternative mechanism to hydrolysis by which the plant cell wall may be loosened. The work described in this thesis is an investigation of this hypothesis. Spinach (<i>Spinacia oleracea</i> L.) cell suspension cultures were incubated with [<i>xylosyl</i>-<SUP>3</SUP>H]xyloglucan nonasaccharide (XG9; Glc<SUB>4</SUB>.Xyl<SUB>3</SUB>.Gal.Fuc) and [<i>reducing terminus</i>-<SUP>3</SUP>H]XG9. The majority of <SUP>3</SUP>H-labelled material remained soluble and extracellular (69-98% ), and 53-57% of it underwent an apparent increase in molecular weight as shown by gel permeation chromatography. This result could suggest the occurrence of a transglycosylation reaction in the apoplast. A proportion of XG9 was hydrolysed to low molecular weight <SUP>3</SUP>H-labelled products. [<SUP>3</SUP>H]-XG9 was found to have undergone no appreciable re-arrangementon incorporation into the high molecular weight product as complete acid hydrolysis and Driselase digestion released similar <SUP>3</SUP>H-labelled hydrolysis products from the putative transglycosylation product, as from [<SUP>3</SUP>H]-XG9. The reducing terminus of the oligosaccharide remained as a reducing terminus of the high molecular weight product. This was shown by sodium borohydride reduction of the product formed during incubation of cells with [<i>reducing terminus</i>-<SUP>3</SUP>H]XG9. This would suggest that XG9 acts as the acceptor substrate, an apoplastic donor being cleaved and the newly formed potentially reducing terminus of this polymer being transferred onto XG9.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:662178 |
| Date | January 1992 |
| Creators | Smith, Rachel C. |
| Publisher | University of Edinburgh |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | http://hdl.handle.net/1842/12139 |
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