Browsing by Author "Driouich, Azeddine"
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- ItemOpen AccessCell wall involvement in desiccation tolerance in the resurrection plant Craterostigma wilmsii(2001) Vicre, Maїté; Farrant, Jill M; Driouich, AzeddineResurrection plants have the unique capacity to revive from an air-dried state. In order to cope with desiccation, resurrection plants have to overcome a number of stresses, mechanical stress being one. This occurs when the cytoplasm shrinks creating tension between the plasma membrane and the cell wall. In leaves of the Craterostigma species, an extensive shrinkage occurs during drying as well as a considerable wall folding. It is thought that this folding is a well controlled process rather than a simple collapse and that the ability of the wall to fold is important for the viability of the tissues upon drying. The aim of this study was to characterize the cell wall architecture and composition in hydrated and dry leaves of C. wilmsii using microscopical and biochemical techniques. Calcium and hormone contents were also determined during drying. The development of anhydrous fixation for microscopy confirmed the important folding of the wall previously observed with chemical fixation. Using immunocytochemical techniques and a variety of well characterized antibodies, the nature and composition of wall polymers was investigated. There was nothing unusual in the wall composition of C. wilmsii leaves as compared with other dicotyledonous plants. The results show a significant increase of the hemicellulosic polysaccharide xyloglucan and of the unesterified pectins during drying with levels declining again during rehydration. In contrast no increase was observed in others polysaccharides such as ß (1-4) galactans and methylesterified pectins. Biochemical analysis allowed further characterization of cell wall composition of C. wilmsii. The data demonstrate marked changes in the pectic and hemicellulosic wall fraction from dry plants compared to hydrated ones. The most conspicuous change was a decrease in glucose content in the hemicellulose fraction of the dry plant. Together these findings show that dehydration causes important alteration of polysaccharides content in the cell wall of C. wilmsii. Such modifications might be involved in the modulation of the mechanical properties of the wall during dehydration. Furthermore calcium ions content was shown to increase in the cell wall of dry plants, this could also have a role in stabilizing the wall architecture. All these alterations might be under the control of auxin, an hormone whose content was shown to increase during dehydration.
- ItemRestrictedResponse of the leaf cell wall to desiccation in the resurrection plant Myrothamnus flabellifolius(American Society of Plant Biologists, 2006) Moore, John P; Nguema-Ona, Eric; Chevalier, Laurence; Lindsey, George G; Brandt, Wolf F; Lerouge, Patrice; Farrant, Jill M; Driouich, AzeddineThe Myrothamnus flabellifolius leaf cell wall and its response to desiccation were investigated using electron microscopic, biochemical, and immunocytochemical techniques. Electron microscopy revealed desiccation-induced cell wall folding in the majority of mesophyll and epidermal cells. Thick-walled vascular tissue and sclerenchymous ribs did not fold and supported the surrounding tissue, thereby limiting the extent of leaf shrinkage and allowing leaf morphology to be rapidly regained upon rehydration. Isolated cell walls from hydrated and desiccated M. flabellifolius leaves were fractionated into their constituent polymers and the resulting fractions were analyzed for monosaccharide content. Significant differences between hydrated and desiccated states were observed in the water-soluble buffer extract, pectin fractions, and the arabinogalactan protein-rich extract. A marked increase in galacturonic acid was found in the alkali-insoluble pectic fraction. Xyloglucan structure was analyzed and shown to be of the standard dicotyledonous pattern. Immunocytochemical analysis determined the cellular location of the various epitopes associated with cell wall components, including pectin, xyloglucan, and arabinogalactan proteins, in hydrated and desiccated leaf tissue. The most striking observation was a constitutively present high concentration of arabinose, which was associated with pectin, presumably in the form of arabinan polymers. We propose that the arabinan-rich leaf cell wall of M. flabellifolius possesses the necessary structural properties to be able to undergo repeated periods of desiccation and rehydration.