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Rumen Microbial Degradation of Starch-Containing Bundle Sheath Cells in Warm-Season Grasses¹

Leaf sections of the warm-season grasses ‘Coastal’ bermudagrass (Cynodon dactylon (L.) Pers.), ‘Pensacola’ bahiagrass (Paspalum notatum Flugge), and ‘Pangola’ digitgrass (Digitaria decumbens Stent.) were evaluated for the ease of rumen microbial degradation of cells with high nutrient contents using electron microscopy. Observations of IKI-stained sections viewed by light microscopy confirmed those of others in that most starch was found in the chloroplasts of parenchyma bundle sheath cells while little or no starch was seen in mesophyll chloroplasts. Parenchyma sheath cells were less rapidly degraded than mesophyll cells in all species. Observations from transmission electron microscopy revealed that in these warm season grasses starch was undegraded until the thick, laminated wall of the parenchyma sheath was degraded or disrupted by rumen bacteria; starch grains were then degraded. These results indicated that the large amount of potential nutrients in the parenchyma bundle sheath of these warm-season forages may not be readily available because of slow degradation of the sheath cell wall by rumen bacteria.

Key Words: Coastal bermudagrass • Cynodon dactylon • Pensacola bahiagrass • Paspalum notatum • Pangola digitgrass • Digitaria decumbens • Electron microscopy

² Microbiologist and research chemist, Field Crops Research Laboratory, Richard B. Russell Agricultural Research Center, ARS, USDA, Athens, GA 30604.