Cross-sections of available forage and extrusa fractions of leaf blades of Tanzânia-1, Mombaça and Massai grasses were evaluated for anatomic structure and observations of residue of in vitro digestibility. The observations showed greater frequency of scherenchyma girders in leaf blades of cv Massai, compared with order grasses. Tanzânia-1 and Mombaça residues were more susceptible to digestion, while Massai presented more frequently scherenchyma girders associated with less digestible bundle sheath

da Graça Morais, Maria

Euclides, Valéria P. B.

Lempp, B.

Victor, D. M.

English

University of Kentucky

University of Kentucky UKnowledge International Grassland Congress Proceedings XIX International Grassland Congress Observation of Bundle Sheath Digestion of Panicum maximum Jacq, B. Lempp Universidade Federal de Mato Grosso do Sul, Brazil Valéria P. B. Euclides EMBRAPA, Brazil Maria da Graça Morais Universidade Federal de Mato Grosso do Sul, Brazil D. M. Victor Universidade Federal de Mato Grosso do Sul, Brazil Follow this and additional works at: https://uknowledge.uky.edu/igc  Part of the Plant Sciences Commons, and the Soil Science Commons This document is available at https://uknowledge.uky.edu/igc/19/9/31 This collection is currently under construction. The XIX International Grassland Congress took place in São Pedro, São Paulo, Brazil from February 11 through February 21, 2001. Proceedings published by Fundacao de Estudos Agrarios Luiz de Queiroz This Event is brought to you for free and open access by the Plant and Soil Sciences at UKnowledge. It has been accepted for inclusion in International Grassland Congress Proceedings by an authorized administrator of UKnowledge. For more information, please contact UKnowledge@lsv.uky.edu. ID#09-37OBSERVATION OF BUNDLE SHEAT DIGESTION OF Panicum maximum Jacq.B. Lempp1, V.B.P. Euclides2, M. da. G. Morais1, and D.M. Victor11Universidade Federal de Mato Grosso do Sul, C. P. 533, Dourados, MS, 79804-970, Brasil2 Embrapa Gado de Corte, Caixa Postal 154, Campo Grande, MS, 79002-970, BrasilAbstractCross-sections of available forage and extrusa fractions of leaf blades of Tanzânia-1,Mombaça and Massai grasses were evaluated for anatomic structure and observations ofresidue of in vitro digestibility. The observations showed greater frequency of scherenchymagirders in leaf blades of cv Massai, compared with order grasses. Tanzânia-1 and Mombaçaresidues were more susceptible to digestion, while Massai presented more frequentlyscherenchyma girders associated with less digestible bundle sheath.Keywords: Massai, microscope, Mombaça, Tanzânia-1.IntroductionObservations of leaf blades digestion residue revealed variation in the ease with whichtissues are digested by rumen microbes, i.e. mesophyll is rapidly digested whereasparenchyma bundle sheath is very slow. The chemical nature of bundle sheath, however is notwell known. The walls of bundle sheath cells in C4 grasses are different from those of themesophyll cells. They show secondary thickening, are about five times the thickness ofmesophyll walls (Wilson, 1990), and are weakly lignified as judged from safranin O staining(Lempp, 1997).  The C4 grasses contain a high proportion of bundle sheath, with are rich inprotein and starch and hence are a significant source of easily digestible constituents. ForPanicum maximum this proportion reached 29.40 % (Lempp, 1997). The apparentlignification, however, does not prevent digestion but may render it incomplete and alwaysslow, taking 48 to 72 h or longer (Akin et al., 1983). These cells may influence dry matterdigestibility due to the characteristics of their walls which determine the availability of theirpolysaccharides to rumen microbes. Our objective was to evaluate the bundle sheath cellsdigestibility by observation of leaf blades digestion residue and beef cattle feces.Material and MethodsThis research was performed at Embrapa Beef Cattle Research Center (CampoGrande, MS, Brazil). The experiment was conducted in Panicum maximum cvs Massai,Mombaça, and Tanzânia-1 plots. Samples were  collected from three oesophagally-fistulatedsteers in December of 1998. The extrusa of each animal was collected in four consecutivedays, homogenized, and leaf blade fragments were manually separated. Additionally,excrements of four steers were collected and observed under a light-microscope. Fragments ofleaf blades from extrusa in natura (1-2 g) were placed in nylon bags (40 µm pores – 12 cm2)and incubated (Tilley and Terry, 1963). After six, 12, 24, 48, and, 72 h were fixed informalin-acetic acid-alcohol (FAA). Ten microscope slides with the incubation residue ofeach sample/time was observed in a light-microscope, and photographed. Samples of leafblade fragments consisted of a one centimeter section from the median portion of thepenultimate expanded leaf blade. Each sample was preserved in FAA, processed according toDaykin and Hussel (1985). Transverse sections of 10 µm were safranin O (red) stained forobservations at the light microscope.Bundle sheath cells were retained by a 248 µm nylonmesh (modified from Grabber and Jung, 1991). Cell wall analyses were then performed.Results and DiscussionObservations under the light-microscope of digestion residues indicated negligibledifferences among cultivars after six, 12, and 24 h of incubation.  The slight differences inrelation to bundle sheath cell disappearance at those times could be a result of slowdigestibility of the cells compared to mesophyll cells. Mesophyll cells almost disappearedafter the 24 h incubation period. The thickness of bundle sheath cell walls  may  explain theslow digestion. Akin and Burdick (1975) studying the bundle sheath cells of Cynodondactylon observed a laminated cell wall structure  of  0.5 to 1.0 µm in width, and a possiblelignification of the cell wall. In our study the quadruple-stain triarch technique  of the tissuesrevealed a positive reaction  to the safranin O in the bundle sheath cells for the three cultivarsstudied, indicating the presence of phenolic compounds. Differences among cultivars weremore evident after the 48 h incubation period. Greater digestion of bundle sheath cells of cvs.Tanzania-1 and Mombaça were observed compared to cv. Massai (Figure 1). In the cv.Massai residue, a frequent detachment of the bundle sheath cells after 48 and 72 h ofincubation could be observed, as well as few cell wall residues and structured leaf bladefragments. Microscopic observations of leaf blades from available forage revealed greaterfrequency of sclerenchyma girder (arrangement of epidermal  cells and bundle sheath cellsthrough sclerenchyma cells)  for the Massai in relation to the other two cultivars. This specificanatomical arrangement interferes with the middle lamella dissolution, consequently leadingto longer retention time of the particles in the rumen (Wilson et al., 1989). Microscopicobservations of excrements also confirmed the low digestibility of the Massai bundle sheathcells detected by the digestion residue observations.  A high frequency of detached cells aswell as adhered to the vascular tissue were noticed in the excrements (Figures 2A and 2B).The Massai digestion residue at the 72 h was very similar to the excrement residues.Variations in the chemical cell wall composition might explain the lower digestibility ofMassai bundle sheath cells. Although, tropical grasses are divided into three groups: PCK,NADP-ME, and NAD-ME, the chemical nature of the cell wall has not been described. Akinet al. (1983) and Wilson and Hattersley (1983) reported differences in the bundle sheath celldisappearance average in Panicum spp. (C4) after a 20 h incubation period in vitro, 23.0 % forNAD-ME and 73.6 % for PCK. Mestoma sheaths were observed in all cultivars studied. Thus,these cultivars are either NAD-ME or PCK, and differences in digestibility could be explainedby the chemical composition of the cell wall. Although, a complete isolation of bundle sheathcells was not possible, similar levels of hemicellulose, lignin, NDF, and ADF were observedamong the three cultivars. Greater variation was observed for cellulose levels were 28.6 %,31.3 %, and 36.6 %, for Tanzânia-1, Mombaça, and Massai, respectively. Observations of leafblades transverse sections, digestion residues, and excrements showed that Massai has a lowerdigestive weakening and bundle sheath cells digestibility.  Barbosa and Euclides (1997)reported less  weight gaining of beef cattle fed with Massai compared to Tanzânia-1 andMombaça. Our findings could explain that fact. Future studies should be directed towards thedigestibility of Massai bundle sheath cells, to investigate differences in the chemical nature ofits cell structure, and if these differences interfere with the accessibility of rumenmicroorganisms to the cell wall.ReferencesAkin, D.E. and Burdick D. (1975). Percentage of tissue types in tropical and temperate grassleaf blades and degradation of tissues by rumen microorganisms. Crop Sci. 15: 661-668.Akin, D.E., Wilson J.R. and Windham W.R. (1983). Site and rate of tissue digestion inleaves of C3,C4 and C3/C4 intermediate Panicum species. Crop Sci. 23: 147- 155.Barbosa, R.M. and Euclides V.P.B. (1997). Valores nutritivos de três cultivares In ReuniãoAnual da Sociedade Brasileira de Zootecnia, 34, 1997, Juiz de Fora, Anais...v.2, pp.53-55.Daykin, M.E. and Hussel R.S. (1985). Staining and histopathological techiniques innematology. Backer, K.R.; Carter, C.C.; Sasser, J.N. (Eds.). An advance treatise onMeloidogyne. Releigh: North Caroline State University Grafics, pp.39-48.Grabber, J.H. and Jung G.A. (1991).Isolation of parenchyma and sclerenchyma cell typesfrom the plant parts of grasses.Crop Sci.  31: 838-844.Lempp, B. (1997). Avaliações qualitativas, químicas, biológicas e anatômicas de lâminas dePanicum maximum Jacq. Cv. Aruana e Vencedor. Jabotical, SP: UNESP 148p. Tese(Doutorado em Zootecnia) - Universidade Estadual Paulista.Tilley, J.M.A. and Terry R. A. (1963). A two – stage technique for the in vitro digestion offorage crops. J. Br. Grassl. Soc. 18: 104-111.Wilson, J.R. (1990). Influence of plant anatomy on digestion and fibre breakdown . pp. 99-117. In D.E. Akin et al. 9ed.). Microbial and plant opportunities to improve the utilisation oflignocellulose by ruminants. Elsevier Sci. Publ. Co., New York.Wilson, J.R. and Hattersley P.W. (1983). In vitro digestion of bundle sheath cells in rumenfluid and its relation to the suberized lamella and C4 photosynthetic type in Panicum species.Grass For. Sci.38: 219-233.Wilson, J.R., Akin D.E., McLeod M.N. and Minson D.J. (1989). Particle size reduction ofthe leaves of a tropical and a temperate grass by cattle. II. Relation of anatomical structure tothe process of leaf breakdown through chewing and digestion. Grass  For. Sci. 44: 65-75.Figure 1 - Digestion residues of leaf blades extrusa after 48h h in vitro incubation, → cellwall residue A. cv Mombaça. B. cv. Tanzânia-1. C. cv. Massai, structured leaf bladefragment. ( 20 µm).Figure 2 - A e B. Leaf blades fragments of  Panicum maximum cv Massai in feces. C.Isolated bundle sheath cells of leaf blades of cv Massai. → Bundle sheath cells ( 20 µm).B C↓A B C→  → →

Observation of Bundle Sheath Digestion of \u3ci\u3ePanicum maximum\u3c/i\u3e Jacq,

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Observation of Bundle Sheath Digestion of \u3ci\u3ePanicum maximum\u3c/i\u3e Jacq,

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