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Relationships of Different Histochemical Types of Lignified Cell Walls to Forage Digestibility¹

Cell walls of leaf blades of several grasses were examined both for their reactions with lignin stains and for their digestibility by rumen microorganisms. Thin sections were tested for lignin with acid phloroglucinol and chlorine-sulfite stains. Cell wall digestion was determined by incubation (in vitro) of leaf blades with rumen microorganisms and examination with electron microscopy. In general, the rigid and supportive cell walls of the vascular bundles (i.e., inner bundle sheath and xylem cells) that stained positive for lignin with acid phloroglucinol were totally undergraded by rumen microorganisms. Sclerenchyma tissue was degraded only at the periphery by normal, adhering rumen microorganisms; however, occasionally digestion was extensive and was associated with an unusual or filamentous bacterium. When treated with chlorinesulfite, sclerenchyma cell walls of all grasses showed a definitive positive reaction for lignin. However, chlorine-sulfite stain also revealed the presence of lignin in cell walls of certain living cells in some grasses. Included were cell walls of the parenchyma bundle sheath of bermudagrasses [Cynodon dactylon (L.) Pers.] and the parenchyma sheath, mesophyll (occasionally) and abaxial epidermis of tall fescue (Festuca arundinacea Schreb.) These tissues in leaf blades from similar or the same harvests were only slowly or partially degraded after 24 to 72 hours. Further examination of Coastal bermudagrass revealed that portions of the parenchyma bundle sheath resisted in vitro digestion for 8 days, and also were present in the fecal residue along with the xylem and sclerenchyma tissues. In these studies, the extent of forage digestion appeared to be determined by the rigid, acid phloroglucinol-positive cell walls of the vascular bundles, the sclerenchyma (except for cells at the periphery and those cells degraded by the filamentous bacterium), and variable amounts of cell walls of living tissues which often gave a positive chlorine-sulfite reaction.

Key Words: Electron microscopy • Acid phloroglucinol • Chlorine-sulfite • Lignin • Bermudagrass • Tall fescue • Timothy • Orchardgrass

² Microbiologist and research chemist, Field Crops Laboratory, Richard B. Russell Agricultural Research Center, SEA-AR-USDA, Athens, GA 30613.

Received for publication September 22, 1980.

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