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Maize Stem Tissues

Impact of Development on Cell Wall Degradability

^a USDA-ARS Plant Science Res. Unit and U.S. Dairy Forage Res. Center Cluster, Univ. of Minnesota, Dep. of Agronomy and Plant Genetics, 411 Borlaug Hall, 1991 Upper Buford Circle, St. Paul, MN 55108
^b USDA-ARS U.S. Dairy Forage Res., 1925 Linden Drive West, Madison, WI 53706

View larger version (139K): [in a new window]   Fig. 1. Micrographs showing stem internode tissues of maize hybrid 632 at full physiological maturity (mature grain, Sampling Date 10) remaining after in vitro degradation by rumen microbes for 24 or 96 h. The images were created by combining two adjacent fields of view. The double-ended arrow indicates the approximate width of the rind region that remained nondegraded. Bar = 500 µm; par, parenchyma; scl, sclerenchyma.

View larger version (196K): [in a new window]   Fig. 2. Rind-region tissues from maize hybrid 679 at Sampling Dates 4 (a) and 10 (d) and after in vitro degradation by rumen microorganisms for 24 (b, e) or 96 h (c, f). Bar = 40 µm; epi, epidermis; mx, metaxylem; par, parenchyma; phl, phloem; px, protoxylem; scl, sclerenchyma.

View larger version (21K): [in a new window]   Fig. 3. Degradability of total cell wall polysaccharides after 24- and 96-h in vitro incubations with rumen microorganisms for the fourth elongated internode above ground level, averaged across maize hybrids 632, 679, and 2677, sampled at 10 stages of development. The arrow located between the fifth and sixth sampling dates represents the approximate time when elongation of the internodes ceased. LSD, least significant difference (P < 0.05).

View larger version (33K): [in a new window]   Fig. 4. In vitro ruminal degradability of cell wall polysaccharide component sugars after 24- (a, c) and 96-h (b, d) incubations for maize stem internodes, averaged across three hybrids, as influenced by stage of development. The arrow located between the fifth and sixth sampling dates represents the approximate time when elongation of the internodes ceased. Least significant difference values (P < 0.05) for 24- and 96-h degradability, respectively, were glucose = 55, 48; xylose = 128, 81; uronic acids = 37, 30; arabinose = 41, 42; galactose = 54, 41; mannose = 48, 19. Ara, arabinose; Gal, galactose; Glc, glucose; Man, mannose; UA, uronic acids; Xyl, xylose.

View larger version (21K): [in a new window]   Fig. 5. Relationships of total cell wall polysaccharide degradability with Klason lignin (a) and ferulate ether (b) concentrations for maize stem internodes, averaged across three hybrids and 2 yr, after 24- () and 96-h () in vitro ruminal incubations for 10 sampling dates. The arrow located between the fifth and sixth sampling dates represents the approximate time when elongation of the internodes ceased. Bars represent one standard error of the mean. Absence of error bars indicates that the standard error was smaller than the size of the data symbol. Linear regressions were calculated for degradability with Klason lignin (24 h = 956 – 3.61KL, r2 = 0.99; 96 h = 1067 – 3.51KL, r2 = 0.99) and polynomial regressions of degradability with ferulate ethers (24 h = 903 – 46.00FE – 9.29FE2, r2 = 0.998; 96 h = 937 – 4.66FE – 13.45FE2, r2 = 0.999). Sampling Dates 1 through 3 and 8 through 10 were excluded from the regressions for Klason lignin and ferulate ethers, respectively.

View larger version (22K): [in a new window]   Fig. 6. The impact of ferulate ether cross-linking frequency with Klason lignin on total cell wall polysaccharide in vitro ruminal degradability of maize internodes sampled at 10 developmental stages. Data are means across three maize hybrids and two growth years. Linear regressions for degradability with ferulate/Klason lignin cross-linking frequency of elongating internodes (Sampling Dates 1 through 5: 24 h = 952 – 3.59X, r2 = 0.74; 96 h = 989 – 2.60X, r2 = 0.79) and post-elongation internodes (Sampling Dates 5 through 10: 24 h = 128 + 6.84X, r2 = 0.85; 96 h = 261 + 6.69X, r2 = 0.82) were calculated.