Cell wall fractionation of alfalfa stem in relation to internode development: biochemistry aspect
1998
Vallet, C. | Lemaire, G. | Monties, B. | Chabbert, B.
In addition to morphological factors (height of the plant, proportion of stems), alfalfa quality is related to several biochemical factors, especially the content and monomeric composition of the cell wall components. This work was aimed at studying internode development in relation to the chemical composition and fractionation of cell walls. Analyses were performed on the fourth apical internodes (elongating), the two following ones (onset of cambial activity), and bottom internodes (mature). Deposition of guaiacyl type lignin occurred in the pectin rich cell walls of apical internodes. The onset of cambial activity corresponded to cell wall accumulation of syringyl-guaiacyl lignin, xylans and/or glucuronoxylans, and cellulose. Such events were related to the thickening of secondary cell walls which proportion increased in mature internodes. Chemical fractionation of the cell walls allowed the release of a high content of water soluble pectins from apical internodes, whereas alkalis were more efficient in extracting heteroxylans from bottom internodes. A partial release of lignin from the cell walls also occurred during the extraction steps. Lignin solubilization was enhanced by the cleavage of labile-ether lignin structures and appeared closely related to the extent of internode differentiation along the stem. Data gained from chemical fractionations evidenced that lignin-xylan-pectic complexes accumulated progressively in secondary wall rich tissues.
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