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ARS Home » Midwest Area » St. Paul, Minnesota » Plant Science Research » Research » Publications at this Location » Publication #89201
Title: ACCESSIBILITY LIMITS CELL-WALL DEGRADATION OF ALFALFA STEM TISSUES

Author
item Jung, Hans Joachim
item ENGELS, FERDINAND - WAGENINGEN AGRIC UNIV

Submitted to: American Dairy Science Association Abstracts
Publication Type: Abstract Only
Publication Acceptance Date: 7/29/1998
Publication Date: N/A
Citation: N/A

Interpretive Summary:

Technical Abstract: The lignified primary cell wall in forages is hypothesized to constitute an impenetrable barrier for access by rumen microbes to potentially degradable cell-wall polysaccharides. This hypothesis was tested by incubating 2-cm long alfalfa stem pieces in rumen fluid for 24-h. A wax coating was applied to the stem pieces to prevent microbial access to the alfalfa tissues, except for one end which was exposed by cross-sectioning. After the incubations, the stem pieces were serially sectioned (100 um thick) starting from the exposed end. Degradation of tissues was examined in depth by light microscopy. Phloroglucinol staining was used to identify lignified tissues. Examination of stem pieces from two harvest years indicated that non-lignified, thin- and thick-walled tissues (such as protoxylem parenchyma and collenchyma, respectively) were degraded to great depth (up to 8000 and 5600 um, respectively). Using longitudinal sectioning of non-degraded control stems to determine cell lengths, it was apparent that degradation had penetrated through many cell layers of these tissues. Tissues which developed a lignified middle lamella/primary wall (such as cortical and xylem fibers) were only degraded in the initial cell layer exposed to the rumen microbes by sectioning. Cell layers deeper in the stem piece were not degraded. Presence of undegraded, non-lignified secondary wall layers in cortical and xylem fibers in sections taken further down the stem piece than the length of one cell for these tissues provided proof that the lignified primary wall was an impenetrable barrier to rumen microbes. These results highlight the importance of particle size reduction to maximizing forage cell-wall utilization and identifies the lignified primary wall as a target for modification to improve forage quality.