|Jung, Hans Joachim|
|Engels, Ferdinand - WAGENINGEN AGRIC UNIV, NL|
Submitted to: Conference on Rumen Function
Publication Type: Abstract Only
Publication Acceptance Date: November 11, 1997
Publication Date: N/A
Technical Abstract: We examined the impact of maturation in alfalfa stems on limitations to cell wall degradability. The seventh internode of regrowth stems was collected at five stages of development. The seventh internode was in the elongation phase of development at the first and second harvests. By the third harvest most internodes had completed elongation. The fourth harvest was taken after 31 d of regrowth and all stems were flowering. During internode elongation all tissues had thin, degradable primary walls except protoxylem, which was already well developed and lignified as indicated by phloroglucinol staining, and remained undegraded after a 48 h in vitro fermentation of 100 micron thick sections. By the third harvest secondary xylem, xylem fibers, cortical fibers, and pith parenchyma began to deposit secondary cell walls and lignify. These tissues became undegradable. Lignification always began in the thin primary cell walls. Cortical fibers developed a thin, ring shaped lignified part of the primary wall prior to deposition of a thick secondary wall which never lignified and remained degradable. Non-lignified tissues remained degradable throughout maturation. When 1.5- to 2-cm long stem pieces from the fourth harvest were fermented in vitro for 24 h, degradability of tissues was altered compared to fermentation of thin sections. Those tissues that had non-lignified primary walls were rapidly degraded and the degradation front passed through many cell layers to depths of 1 cm in stem pieces. In contrast, any tissue that had deposited lignin in the primary wall was only degraded in the cell layer actually exposed at the cut end. Even the non-lignified, potentially degradable secondary wall of cortical fiber cells was not degraded in the cell layer immediately below the cut end of the stem.