Chemical analysis

Fiber bundles were ground with a ball crusher (Retsch, MM 2000) and extractives were removed using 80% ethanol at 40°C (20 ml/200mg, 4 times), then dried. Complete acid hydrolysis of cell wall polysaccharides into sugar monomers was performed using 1 M H₂SO₄ for 2 h at 100°C. The released monosaccharides were separated by high performance anion-exchange chromatography (PA1 column, Dionex) and analyses performed in triplicate as previously described [27]. Lignin content was estimated by a spectrophotometric procedure using acetyl bromide and 15 mg of cell wall residue (CWR) as previously described [28].