Composition and distribution of cell wall phenolic compounds in flax (Linum usitatissimum L.) stem tissues

Cell wall phenolic compounds were analysed in xylem and bast fibre-rich peels of Bar stems by biochemical, histochemical and ultrastructural approaches. Localization of cell wall phenolics by the enzyme-gold method using laccase revealed several gold particle distribution patterns. One of the major types (an even distribution of single gold particles) was present mainly in xylem, while the other (compact branched groups of ten-40 gold particles) was found both in xylem and fibre cells. The lignin content of the stem parts was estimated by the Klason procedure and by the thioglycolic acid assay, and the phenolic products recovered after alkaline cupric oxide oxidation of cell walls were analysed by GC. By combining chemical analysis data and the frequency of various gold particle types within the tissues, different patterns of gold particle distribution could be ascribed to certain cell wall phenolics; lignin was stained as evenly distributed single gold particles, while branched clusters represented hydroxycinnamic acids. The Klason procedure did not remove all the non-lignin components from flax fibres, known for their highly crystalline cellulose, and considerably overestimated the lignin content. The thioglycolic acid assay results were consistent with GC and microscopic observations. (C) 2000 Annals of Botany Company.