Dynamique du positionnement de la cellulose dans les parois des fibres textiles du lin (Linum usitatissimum)

Abstract

Resume.-Les parois des fibres des tiges de lin qui produisent un textile et des etoffes exceptionnelles ont une architecture cellulosique, traditionnellement decrite avec trois regions "spirales" majeures (Sl, 82-Ires dominante a structure tendant a devenir axiale -, 83) dans lesquelles !'orientation des microfibrilles reste parallele et constante (unidirectionnelle). II est montre ici que les changements d'orientation, aux interfaces de ces formations dominantes, font intervenir des plans intermediaires constitues d'arcs emboites, accentuables par goniometrie, doni I' organisation est celle d'analogues cholesteriques (structures helico'idales temporaires multidirectionnelles). Une modelisation de ces parois dans le temps et dans l'espace est proposee ; les mecanismes possibles de Ia morphogenese sont discutes en prenant en compte une cooperation entre un assemblage dirige (via le plasmalemma) et un auto-assemblage de type cristal liquide (analogue cholesterique intermittent). La comparaison de cette structure parietale avec celle des sclerites isodiametriques, ou les helico'ides se developpent de lacon continue, indique que Ia forme cellulaire parait etre un element determinant dans !'expression de !'architecture cholesterique et done des proprietes mecaniques (tenacite) de Ia fibre.Summary.-The cell wall of stem fibers of flax shows the classical cellulosic architecture with three main domains with constant slope (Sl, 82-thickened and locked into an almost axial direction-, 83) within which the microfibril orientation remains parallel (unidirectionnal, the so-called "spiral texture"). The present paper focus on the fact that arced change of orientation occurs at the major wall layer interfaces. The nested arcs are cancelled or reversed by tilting of the goniometric stage at the electron microscopy level ; they are transient cholesteric analog (multidirectional helicoids). Structural models are provided giving unified picture of the flax fiber wall according space and time. Data are consistant with a possible dual mechanism controlling the cellulosic framework morphogenesis: cooperation between a directed assembly (via the plasmalemma) and a liquid crystal-like self assembly. The secondary cell wall of fibers with intermittent cholesteric pattern is compared to the secondary cell wall of isodiametric sclereid with continuous cholesteric pattern and cell shapes appear essential for the expression of such architecture and thus of the mechanical properties (tenacity) of the fiber.

Investigation of the internal structure of flax fibre cell walls by transmission electron microscopy

“…Some authors hypothesized the same structure for flax fibre as for wood (Baley et al 2005; Bos and Donald 1999) and reported a relative thickness of 8-15 % for S1 and S3, 70-80 % for S2 and 1-4 % for P. Others have experimentally observed the structure of the bevelled-cut section of flax fibre (Roland et al 1995) and highlighted three distinct layers together with the middle lamellas. However, the transition zones between S1 and S2 or S2 and S3 do not clearly appear and thus no sub-layers could be identified.…”

“…However, the thickness of these sub-layers is higher than the S3 layer generally described in the classical four layer model; • The S3 layer defined in the four layer model should be the inner sub-layer and the others sub-layers would be a ''transition domain''. Indeed, Roland et al (1995) have hypothesized that the change in the microfibrils angle between the layers of the cell walls should occurs gradually through transition layers. Thus, it can be suggested that the transition between S2 and S3 occurs more progressively than the transition between S1 and S2 and that may explain why transition layers cannot be observed in the latter case.…”

“…[ (Baley et al 2005;Bos and Donald 1999;Brett and Waldron 1996;Nilsson and Gustafsson 2007;Preston 1974;Roland et al 1995).…”

Secondary cell-wall assembly in flax phloem fibres: role of galactans

“…The term gelatinous fibres is generally used for tension wood fibres but is also applicable to the other non-lignified fibres as they accumulate gel-like polymers during development (Anderson 1926;Gorshkova et al 2005). The principal characteristics of the secondary wall of gelatinous fibre cells are (1) the high content of cellulose (Roland et al 1995), (2) the small amount of phenolics, being mainly G units (Joseleau et al 2004;Pilate et al 2004), (3) the cellulose microfibrils running largely parallel to the longitudinal axis of the cell (Wang et al 2001), and (4) the high proportion of galactose-containing polymers within the non-cellulosic polysaccharides (Meier 1962;Ruel and Barnoud 1978). The secondary cell-wall galactans have been extensively studied in flax fibres (reviewed in Morvan et al 2003) and flax fibres are therefore an attractive system for the examination of the role of galactose-containing polymers within gelatinous fibres.…”

Identification and partial characterization of proteins and proteoglycans encrusting the secondary cell walls of flax fibres

“…Flax ®bre-cells are several millimetres in length and 15±25 lm in diameter, with thick secondary cell walls. These walls are composed of oriented cellulose micro®brils (Roelofsen 1951;NaÈ slund et al 1988;Hulleman et al 1994;Roland et al 1995) embedded in a matrix of dierent polymers. These polymers can only be extracted with alkali and are referred to as encrusting components (Heude and Bossuyt 1959;Sotton and Monrocq 1977).…”