Lignin deposition and associated changes in anatomy, enzyme activity, gene expression, and ruminal degradability in stems of tall fescue at different developmental stages

Stem tissues of tall fescue (Festuca arundinacea Schreb) were sampled at three elongation stages and three reproductive stages. Anatomical analysis showed the deposition of guaiacyl (G) and syringyl (S) lignin during plant development and the formation of a lignified sclerenchyma ring. A dramatic increase in Klason lignin content was found from elongation stage to reproductive stage. Lignin composition analyzed by gas chromatography- mass spectrometry revealed that S lignin content and S/G ratio increased with stem development but contents of p-hydroxyphenyl (H) and G lignins decreased, during the same period S lignin content and S/G ratio also increased from the younger upper internode down to the older basal internode of the stem, but G and H lignin decreased in parallel. Relative O-methyltransferase activities increased during stem development and in parallel with the lignification process of stem. The pattern of enzyme activity during development varied with the choice of substrate with highest activities seen when substrates were caffeoylaldehyde and 5-hydroxyferulic acid, and lowest activities were seen when caffeic acid and 5 hydroxyconiferyl alcohol were used as substrates. The expression of caffeic acid O-methyltransferase and cinnamyl alcohol dehydrogenase genes increased during the stem elongation stage and remained at high levels during the reproductive stages. The changes at anatomical, metabolic, and molecular levels during plant development were closely associated with lignification and degradability. This study provides an integrated picture of the molecular and chemical events that accompany changes in lignin deposition and ruminal degradability.