Developments in application of light and scanning electron microscopy techniques for cell wall degradation studies.

The results of recent technological developments in light and scanning electron microscopy closely used for research on forage cell wall degradation in ruminants, are reviewed. The indigestibility of forages by rumen microorganisms used to be ascribed mainly to an overall presence of lignin in the plant material. However, early light microscopic observations without application of histochemical staining revealed that some leaf and stem tissues were degraded completely. The early use of lignin detecting dyes, such as acid phloroglucinol or safranin, in light microscopy made it possible to discriminate between lignified undegradable and unlignified degradable plant tissues. The introduction of the scanning electron microscope enabled a further discrimination between degradable and undegradable cell wall and cell wall layers in plant tissues. As a result of continuous improvement of the techniques used in microscopy, e.g. section to slide, mirror sectioning, microspectrophotometry and cryo-ultramilling, forage indigestibility can now be attributed to the specific deposition and location of cutin/suberin or lignin layers inside the plant cell wall. These structural layers form barriers hindering access of rumen microorganisms to degradable parts of the cell wall