CHEMICAL AND STRUCTURAL-ANALYSIS OF FIBER AND CORE TISSUES FROM FLAX

Samples of flax (Linum usitatissimum) stems from the cultivars 'Natasj a' and 'Ariane' were separated into fibre and core fractions and analy sed by gas-liquid chromatographic methods, C-13 CPMAS NMR spectrometry , histochemistry, electron microscopy and UV absorption microspectroph otometry to assist in determining the structure and composition of the se cell walls in relation to quality and utilisation. Analyses from ch romatography and NMR gave similar results for carbohydrate and phenoli c constituents in various samples and in the lower, more mature region s of the stem. Amounts of uronic acids and xylose were lower while amo unts of mannose, galactose and glucose were higher in fibre vs core fr actions. Quantities of phenolic constituents were significantly higher in the core than the fibre, with groups representative of both guaiac yl and syringyl lignins; amounts of phenolic acids were low. NMR showe d a low intensity signal for aromatics in fibre, and it is possible th at such signals arise from compounds in the cuticle rather than the fi bre. Microscopic studies indicated that aromatic constituents were pre sent in core cell walls, cuticle of the epidermis, and cell corners an d middle lamellae of some regions within the fibre tissues. The lignin in fibre appeared to be of the guaiacyl type and may be too low in co ncentration to be unambiguously detected by NMR. Aromatic compounds we re not observed in the epidermis or parenchyma cell walls. Similar ana lyses of dew-retted (unscutched) samples indicated that core tissues w ere mostly unchanged from unretted samples. Retted fibre tissues still contained lignified cell corners and middle lamellae in some regions. The cuticle, which was associated with retted fibres, was not degrade d by dew-retting fungi. Fungi removed interfibre materials in some pla ces and at times degraded the secondary wall near the cell lumen of fi bre cells. Results indicate that microspectrophotometry and histochemi stry are useful to identify the location and type of aromatics in fibr e cell walls.