Methods and means are provided for the modification of the reactivity of plant cell walls, particularly as they can be found in natural fibers of fiber producing plants by inclusion of positively charged oligosaccharides or polysaccharides into the cell wall. This can be conveniently achieved by expressing a chimeric gene encoding an N-acetylglucosamine transferase, particularly an N-acetylglucosamine transferase, capable of being targeted to the membranes of the Golgi apparatus in cells of a plant.