TRANSFORMATIONS OF (C-14-LIGNIN) CELL-WALLS OF WHEAT BY RUMEN MICROORGANISMS

The lower halves of apical internodes of wheat harvested at the flower ing stage were labelled with [U-C-14] phenylalanine (phe) or with [O ( CH3)-C-14] sinapic acid (sin). Cell wall residues (CWR) and saponified residues (SR) were incubated in a fermenter simulating the rumen for 7 days with rumen fluid or without microorganisms (controls). PheCWR w as labelled in all lignin units (measured as aldehydes from nitrobenze ne oxidation), in phenolic acids and slightly in proteins. Labelling o f pheSR was more lignin-specific. SinCWR and sinSR were specifically l abelled in syringyl units of lignin. The fermentation of CWR resulted in phenylpropane-derived unit losses in the following decreasing order : ferulic acid > p-coumaric acid > syringaldehyde > vanillin > p-hydro xybenzaldehyde. If allowance is made for slight losses in controls, 61 , 52, 61 and 63% of the phenylpropanes of pheCWR, sinCWR, pheSR and si nSR, respectively, were transformed into an acid-precipitable fraction , an acid-soluble fraction and (CO2)-C-14. The comparison of pheCWR an d sinCWR degradation showed that syringyl units were solubilised into acid-precipitable molecules to a greater extent than the other lignin units; demethylation of the syringyl units of lignins was also evident from the different productions of (CO2)-C-14. Alkali-resistant lignin s of SR were mainly transformed into acid-precipitable molecules and w ere weakly degraded. Lignin solubilisation and degradation seem to be governed by different mechanisms which depend on both cell wall struct ure and rumen microflora.