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  • 1
    ISSN: 1615-6102
    Keywords: Cell wall ; Cellulose/glucuronoxylan ; Acellular assembly ; Cholesteric analog
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Many plant cell walls are constructed according to a helicoidal pattern that is analog to a cholesteric liquid crystal order. This raises the question whether the wall assembly passes through a true but temporary liquid crystal state. The paper focuses on experiments performed from aqueous suspensions of extracted quince slime, i.e., a cellulose/glucuronoxylan wall composite that presents a helicoidal order when observed in situ, within the enlarged periplasm of the seed epidermal cells. Experiments carried out in acellular conditions showed that a spontaneous reassociation into a helicoidal order can be obtained from totally dispersed suspensions. The ultrastructural aspect of the reassembled mucilage suspension was different according to the resin used (LR White or nanoplast, a water-soluble melamin resin). It was always typically polydomain, and when an order was visible it was cholesteric-like and similar to the in situ native organization. Transition states with many imperfections expressed the difficulty of the system to reassemble in the absence of constraining surfaces. The possible intervention of glucuronoxylan (GX) in the ordered assembly of the microfibrils was checked by: (1) progressive extraction of GX by trifluoroacetic acid (TFA). The extraction was associated to a control of the fraction by analysis of uronic acid contents and observation at the electron microscope level. Extraction of GX provoked the formation of a flocculent mass, the flocculation being more intense when the TFA was more concentrated; (2) progressive change of pH in order to analyze the influence of pH on flocculation. Low pH (ca. pH 3) led also to a flocculation of the suspension, but the floc was reversibly lost after dialysis against distilled water. The results indicate the antifloc role of the GX due to the anionic charges carried by the side-chains. However, the function of GX as helper twisting agent in the cholesteric-like reassembly must not be ruled out.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1615-6102
    Keywords: Cell wall ; Helicoidal texture ; Modelling ; Flexibility ; Cellulose
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary The concept of the cell wall organized in a helicoidal pattern was outlined. When studied in transmission electron microscopy, the observed textures appear as a deceptive figure,i.e., as a “trompe l'oeil”. Difficulties—both technological and visual in the reconstitution of the actual geometry (exposure of the microfibrillar framework, 3-dimensional and 4-dimensional restoration), and the interest of simple modelling to understand the changes in cellulose orientation according to space and time are emphasized. The morphogenesis of helicoidal walls presents two main characteristics: it is both very defined and flexible, thus adaptable to varied programs of differentiation and to different environmental conditions. The observations of various cell examples and of responses to experimental treatments, lead to the following considerations: a) the shift of cellulose occurs continuously with time through a constant mutual angle. The wall seems to be built up as an indefinite continuum and forms a monotonous oscillatory system (unvarying motion); b) the shift of cellulose occurs through a mutual angle variable with time (varying motion, change from monotonous helicoid to bimodal helicoid, or sporadic bursts with arrested motion). The helicoidal wall appears as a fibrous composite with multifunctional possibilities ranging from fluidity to stiffness. The helicoidal assembly is remarkably adaptable to different physiological conditions of growth and specialization.
    Type of Medium: Electronic Resource
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