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Rumen Microbial Degradation of Indiangrass and Big Bluestem Leaf Blades¹

Kansas State University, Manhattan 66506

Abstract

Light and transmission electron microscopy were used to observe relative areas of tissues in undigested leaf samples and ease of tissue disappearance in rumen-digested leaf samples for the two warm-season grasses, Andropogon gerardi and Sorghastrum nutans, in two different growth stages. Undigested, immature (20 d postemergence) leaf blades contained slightly higher parenchyma bundle sheath areas than did undigested, mature (167 d postemergence) leaf blades. Mesophyll remained in digested leaf sections for at least 16 and 32 h in vivo incubation (50 to 75% degraded) for immature plants and 96 and 128 h of incubation (50 to 75% degraded) in mature leaf samples. Parenchyma bundle sheaths resisted degradation more so than did mesophyll. Mature leaf blades subjected to 128 h in vivo (polyester bag) incubation had only 25 to 50% bundle sheath cell degradation. Numerous starch granules were observed in bundle sheath cells for leaf blades of both grasses in both growth stages, but hydrolysis of starch granules did not occur until bundle sheath walls were disrupted. High magnifications of outer tangential and radial walls of bundle sheath cells for digested leaf blades revealed a thin suberin layer that resisted degradation. Cell wall material adjoined by a suberin layer from a bundle sheath cell appeared undegraded depending upon the direction from which bacteria attacked. Light microscopy of mature leaf samples indicated differential degradation of vascular bundles depending on bundle size and stage of development.

¹ Contribution No. 82-463-J, Dept. of Agron. Authors are grateful to A. Paulsen, TEM Laboratory, Division of Biol., for use of the microscope.

² Dept. of Agron.

³ Dept. of Anim. Sci. and Ind.

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