CELL-WALL-ASSOCIATED PEROXIDASES AND LIGNIFICATION DURING GROWTH OF FLAX FIBERS

Cell-wall associated peroxidases were selectively extracted from two defined areas of the flax stem throughout the vegetative development of the plant. The activities of these peroxidases were correlated with the extent of fibre lignification in these stem areas. Lignification of fibres in the hypocotyl (below the cotyledonary node) was well advanced by 5 weeks after emergence but lignification of fibres in the first internode (above the cotyledonary node) was only just evident at this time. The extent of lignification increased at both sites over the next 10 weeks. Extracellular peroxidases and wall bound peroxidases from the hypocotyl and first internode samples were able to oxidise a number of different substrates. Total wall-associated activity reached a maximum level around 7 to 9 weeks which coincided with the period of greatest development of the xylem. Between 11 to 15 weeks there is still considerable wall-associated peroxidase activity present at a time of increasing lignification of fibre cells. Fibre-bearing tissue was dissected from the central xylem core. Enzyme extracts obtained from this tissue had high peroxidase activity and showed little contamination from intracellular constituents. Non-denaturing acidic and basic gel electrophoresis of extracellular samples revealed several anionic and cationic peroxidase isozymes. There were no major qualitative or quantitative differences in the isozyme patterns from plants of different ages. Therefore, it was not possible to assign peroxidases which were specifically involved in fibre lignification. A comparison of peroxidases derived from flax callus with those from stem samples revealed differences in anionic and cationic peroxidase isozymes.