Phenolic components and degradability of the cell walls of the brown midrib mutant,bm3, of Zea mays

Cell walls separated from the leaf blade, leaf sheath and stem of the brown midrib mutant, bm₃, of Zea mays were more degradable by a commercial cellulase than the corresponding part of the isogenic normal inbred cultivar (Tr). The walls of each part of the mutant when compared with the corresponding part of the normal cultivar contained less lignin and bound phenolic components released by treatment with NaOH. The major phenolic components detected were trans-p-coumaric and trans-ferulic acids together with small amounts of their cis isomers and diferulic acid. Cell walls of stem of the mutant contained a total of 17.3 mg g^?1 of these bound acids compared with 9.8 mg g^?1 for leaf sheath and 3.5 mg g^?1 for leaf blade: there was more than twice as much p-coumaric acid in cell walls of stem as in those of leaf sheath and more than seven times as much as in those of leaf blade. When cell walls of the stem from the mutant or the normal cultivar were treated with NaOH their degradability by cellulase was highly correlated with the amounts of phenolic components released by the alkali.     

Severe inhibition of maize wall degradation by synthetic lignins formed with coniferaldehyde

Although the enzymatic or ruminal degradability of plants deficient in cinnamyl alcohol dehydrogenase (CAD) is often greater than their normal counterparts, factors responsible for these degradability differences have not been identified. Since lignins in CAD deficient plants often contain elevated concentrations of aldehydes, we used a cell-wall model system to evaluate what effect aldehyde-containing lignins have on the hydrolysis of cell walls by fungal enzymes. Varying ratios of coniferaldehyde and coniferyl alcohol were polymerised into non-lignified primary walls of maize (Zea mays L) by wall-bound peroxidase and exogenously supplied H₂O₂. Coniferaldehyde lignins formed fewer cross-linked structures with other wall components, but they were much more inhibitory to cell wall degradation than lignins formed with coniferyl alcohol. This suggests that the improved degradability of CAD deficient plants is not related to the incorporation of p-hydroxycinnamaldehyde units into lignin. Degradability differences were diminished if enzyme loadings were increased and if hydrophobic aldehyde groups in lignins were reduced to their corresponding alcohols by ethanolic sodium borohydride. © 1998 Society of Chemical Industry.     

Structure and digestibility of tissues in normal and brown midrib pearl millet (Pennisetum glaucum)

The tissues in leaf blades, midribs, sheaths and stems of normal (N), 5848, and two brown midrib (bmr) mutants, 5753 and 5778, of pearl millet (Pennisetum glaucum (L) R Br) were examined for structural characteristics related to digestibility. The anatomies of the various plant parts were not substantially different between N and bmr plants. The more rigid, lignified tissues such as vascular bundles in all plant parts and the rind of stems were not digested after incubation for 7 days in N or bmr plants, indicating that modifications in these tissues were not sufficient to affect biodegradation. Modifications in the digestible tissues resulted in faster and more extensive degradation in bmr plants, and these changes appear to be the most significant in relation to biodegradation. The parenchyma of midveins and stems, which occupies c 70 and 60% of the cross-sectional area of these respective parts, were the sites where modification in phenolics resulted in the greatest improvement in digestibility.     

Apparent inhibition to digestion by lignin in normal and brown midrib stems

Lignin, a cell wall component, limits digestibility of plant cell walls. Brown midrib (bmr) mutants of forages have lignin with altered chemical composition compared with their normal counterparts. The objectives of this study were to determine if bmr lignin is more inhibitory to digestion than is normal lignin and if bmr has a consistent effect on rate of digestion across species and environments. Extent and rate of in-vitro cell wall digestion of normal and bmr stems of sorghum (Sorghum bicolor (L) Moench, two comparisons), millet (Pennisetum americanum (L) Leeke) and maize (Zea mays L, two comparisons) were determined. Samples were incubated in rumen fluid, and data were fitted with a first-order, nonlinear model to estimate concentrations of potentially digestible neutral detergent fibre (PDNDF), digestion rate of PDNDF, concentration of indigestible residue (IR), and lag time before digestion. The NDF, acid-detergent fibre (ADF), and acid-detergent lignin (ADL) analyses were conducted sequentially on undigested samples. The IR: ADL ratio was 37% greater for bmr than for normal plants, which indicates that bmr lignin inhibits digestion more than normal lignin per unit of lignin. Digestion rate of PDNDF was faster in bmr than in normal counterparts in one of the two sorghum comparisons (difference of 59%) and in the millet comparison (difference of 27%), but in neither maize comparison. The bmr mutants were lower than normal genotypes in NDF (9%) and ADL (47%) concentrations. The PDNDF concentration was 19% greater for bmr than for normal lines. Thus, decreased lignin concentration in bmr mutants increased the extent of NDF digestion but did not consistently increase the rate of digestion.     

Microbial degradation of normal maize and bm3 maize in the rumen observed by scanning electron microscopy

Samples of internodes and leaf blades from normal and bm3 maize (Zea mays L) harvested at dough to glazing stage were studied separately to determine their dry matter content, wall composition (NDF, ADF and ADL) and digestibility in sacco. For examination by light and scanning electron microscope, fragments 0·5 cm long were cut halfway along the internode beneath the female ear and on the corresponding blade. The wall and lignin contents of the bm3 maize were lower than in normal maize. The bm3 maize had a greater extent and faster rate of internode and blade disappearance in the rumen than normal maize samples. The histological structure of the two maizes was the same, but after 24 h in the rumen the parenchyma of the bm3 maize had degraded faster and the secondary walls of the fibres of its vascular bundles were degraded whereas those of normal maize had remained intact. After 72 h in the rumen the sclerenchyma of normal maize had changed little whereas that of the bm3 maize had much thinner walls and was abundantly colonised by rumen bacteria.     

Preparation and composition of mesophyll,epidermis and fibre cell walls from leaves of perennial ryegrass (lolium perenne) and italian ryegrass (lolium multiflorum)

Cells of mesophyll, epidermis and residual fibrous material were obtained from leaves of Italian and perennial ryegrass harvested at different stages of maturity by mechanical disruption of leaf tissue. Mesophyll cells were selectively removed by filtration through 0.045 mm nylon mesh and remaining non-mesophyll cells centrifuged in metrizamide solutions (56–58% wt to vol.) of known density (1.308–1.329 g cm³ at 5°C) to obtain a pure epidermis cell fraction and a residual fibre fraction. Whole mesophyll cells contributed 63–72%, epidermis 12–15% and the fibre fraction 15–24% to the total leaf dry matter. Fibre values were higher in late-cut samples. Cell walls were prepared from mesophyll and epidermis cells by disruption and washing to remove cell contents. Fibre cells were judged free of cell contents and received no further treatment. Examination of cell wall preparations by light and electron microscopy showed that both mesophyll and epidermis preparations were essentially free from contaminating material. Mesophyll cell walls were uniformly thin (200 nm) while those of epidermis ranged from 2000–3000 nm at the outer face, thinning to 300 nm or less at the inner surface. An electron-light layer (cuticle) of approximately 200 nm thickness was present covering the outer face of the epidermis. The fibre fraction largely consisted of sclerenchyma, but contained, in addition, other vascular cells, detached annular rings and heavily silicified leaf hairs. Analysis of cell walls accounted for 85–90% of dry matter. Cellulose was the major component of all cell walls examined (approximately 40% of dry matter) with xylose residues accounting for a further 11% of mesophyll, 13.5–17.5% of epidermis and 21–25% of fibre cell walls. Arabinose was low in fibre cells but was present in much higher proportions in mesophyll and epidermis walls. The ratio of arabinose to xylose was approximately 1:1.5 for mesophyll, 1:2.5 for epidermis and 1:7.0 for the fibre fraction. The molar ratio acetyl to xylose remained fairly constant at 1:4 regardless of the grass, cell type or maturity of the sample. The uronic acid content of epidermis was higher than that in other cell types and showed an increase with increasing maturity of the grass, reaching over 9% in late-cut samples. Total phenolic material represented 2–3% of mesophyll and epidermis cell walls and 6% of fibre walls. Ferulic acid alone was released from the primary cell walls by saponification and p-coumaric and ferulic acids from the secondary-thickened fibre walls. Crude protein values (NX6.25) were high in mesophyll cell wall preparations and low in epidermis and fibre cell walls. Amino acid patterns were similar for both grasses and cell types but hydroxyproline was found in greater amounts in fibre cell walls than in either epidermis or mesophyll.     

Biological variability in lignification of maize: Expression of the brown midrib bm2 mutation

The cell wall phenolic components in the internodes of three maize genotypes, namely normal, bm2 and bm3 maize, were determined. The bm2 and bm3 brown midrib mutations lowered the lignin content of the bottom, middle and top internodes to a similar extent. However, unlike bm3, the bm2 trait did not induce a sharp reduction of the level of ester-bound p-coumaric acid in maize internodes. The other main alkali labile phenolic acid, ferulic acid, reached similar levels in the three genotypes. The main difference between bm2 and bm3 mutations occurred in the alkyl aryl ether linked structures of the lignin component. In contrast to bm3 lignins, which are characterised by a low syringyl content, the bm2 lignin had a lower content of guaiacyl units than lignin of normal maize internode. Consequently, the syringyl/guaiacyl molar ratio of bm2 lignin gave higher values (2.7–3.2) than those from either normal (0.9–1.5) or bm3 lignins (0.3). The alkali solubility of lignin was also compared between the three genotypes. Incorporation of the bm3 trait in maize led to a high recovery of alkali soluble lignin whereas the bm2 lignin had a similar solubility to the normal one in 2 M NaOH. The monomeric composition of the alkali soluble lignins was consistent with the non-condensed structures of the in-situ polymer. Although the bm3 and bm2 mutations had different effects on lignification, the modification of the cell wall phenolic level was also found in the bm2 maize stem as previously studied.     

Phenolic constituents of cell wall types of normal and brown midrib mutants of pearl millet (Pennisetum glaucum (L) R Br) in relation to wall biodegradability

The cell walls of parenchyma, rind and vascular bundle fractions of pearl millet (Pennisetum glaucum (L) R Br) were isolated from two brown midrib mutants (bmr) 5753 and 5778 and from their normal (N) near-isogenic line. The cell wall content of parenchyma was lower than that of vascular bundle which, in turn, was lower than that of rind. The amounts of ferulic and p-coumaric acids released by NaOH treatment of the cell walls were in the ranges 3-7 mg g^?1 and 2-26 mg g^?1, respectively. Parenchyma cell walls of the N line had the highest content of p-coumaric acid (26 mg g^?1). This content of p-coumaric acid in the N line contrasts with that of bmr 5753 parenchyma (2 mg acid g^?1 walls) and bmr 5778 (7 mg acid g^?1 walls). The concentration of p-coumaric acid was highest in parenchyma cell walls that had been found to be the least digested. Parenchyma, rind and vascular bundle cells walls of the N line had much higher ratios of p-coumaric acid to ferulic acid than the mutants; rind and vascular bundle walls were less digestible than parenchyma. Small amounts of truxillic acid dimers were released by NaOH from the parenchyma walls of bmr 5778. Treatment of parenchyma, rind and vascular bundle cells walls with purified ‘driselase’ (containing xylanases and cellulases) released p-coumaroyl and feruloyl trisaccharides. Between 25 and 53% of the ferulic acid that was released by the NaOH treatment could be accounted for as feruloyl trisaccharide, but only 1-19% of the p-coumaric acid was accounted for as p-coumaroyl trisaccharide.     

14C labelling of lignins of normal and bm3 maizes for fermentation studies

[U-¹⁴C] phenylalanine (phe*) and [O¹⁴CH₃] sinapic acid (sin*) were infused into the cut ends of normal and bm3 maizes (anthesis stage) under or above the last node or at mid-internode, with or without the leaf, in light or in darkness. Radioactivity was measured in the organs, and in phenolic constituents of the cell wall and saponified residues of the bases and tops of the apical inter-node. In both maize genotype labelled under the node the radioactivity was distributed more evenly in the organs with sin* than with phe*. Infusion above the node and at mid-internode greatly increased radioactivity in the bases and tops, respectively. Removal of the leaf only slightly increased the radioactivity, mainly in the bases, and no clear-cut effect of darkness was observed. Phe* labelled the phenolic acids and the three lignin units, but the syringyl units of bm3 maize were only slightly labelled. Sin* specifically labelled the syringyl units, which represented the least condensed fraction of lignins. Both the native and labelled lignins were highly alkali soluble. There were differences in lignin biogenesis between the bases and tops, and between normal and bm3 maizes. The newly formed lignins were slightly different from the native lignins but had similar types of heterogeneity, with variations in the internode and between genotypes similar to those in native lignins. Provided due allowance is made for the distinguishing characteristics of newly formed lignins, the [¹⁴C-lignin] cell walls, which are strongly labelled on complementary structures, seem suitable model substrates for fermentation studies.     

Digestion kinetics of leaf,stem and inflorescence from five species of mature grasses

The objective of this study was to measure the digestion kinetics for mature (green and non‐senescent) components of five grass species using in sacco and in vitro incubations to define rates of degradation and nutrient release. Mature perennial ryegrass, tall fescue, Yorkshire fog, phalaris and paspalum were hand separated into leaf blade, stem and inflorescence (flower head) for incubations. Concentrations of neutral detergent fibre (NDF) in fractions were in the ranges 492–677 (leaf), 626–718 (stem) and 501–677 (inflorescence) g kg^?1 dry matter (DM). Crude protein concentrations in the DM of the respective fractions were 70–236 (leaf blade), 35–77 (stem) and 75–120 (inflorescence) g kg^?1 DM. Soluble DM (% of the total) determined after mincing accounted for 31–54% of leaf, 26–56% of stem and 20–49% of inflorescence and fractional degradation of the insoluble DM was very slow, in the ranges 0.04–0.11 (leaf), 0.03–0.05 (stem) and 0.03–0.08 (inflorescence) h^?1. After 24 h of in vitro incubation, plant nitrogen content became limiting for fermentation in most instances, especially with tall fescue and paspalum. Volatile fatty acid (VFA) production appeared to be similar for leaf, stem and flower fractions, but the proportion of plant DM released as VFA after 48 h was only 7–12%, with a higher value (19%) for tall fescue. Nitrogen concentration in forage DM was not directly related to VFA yield in vitro. In conclusion, the in sacco kinetics suggested slow colonisation of all components, but especially stem, which will limit the rate of nutrient production. Effective degradability was highest for leaf but rates in vivo will depend on the speed and extent of particle size reduction by chewing during eating and ruminating. Copyright © 2005 Society of Chemical Industry     

UV Absorption microspectrophotometry and digestibility of cell types of bermudagrass internodes at different stages of maturity

The walls of sclerenchyma, vascular bundle sheaths, and parenchyma at different maturities (internodes 2, 5, and 7 from the apex) of bermudagrass [Cynodon dactylon (L) Pers] were analyzed by UV absorption microspectrophotometry, and the results were related to wall digestibility. Sclerenchyma walls from internode 2 were degraded by rumen microorganisms, with only the middle lamella remaining. Undegraded sclerenchyma walls gave a UV absorption spectrum similar to that of p-coumaroyl and feruloyl arabinoxylo-trisaccharides isolated from bermudagrass cell walls. Absorption maxima occurred at ? 245 and 320 nm, together with a shoulder at ? 280 nm. Sclerenchyma from the older internodes 5 and 7 showed only partial degradation of the secondary wall adjacent to the lumen. Spectra of undegraded walls from these internodes showed absorption maxima at ? 245 and 285 nm with a shoulder at ? 320 nm. Spectra of sclerenchyma walls that included the middle lamellae gave a higher absorption at ? 320 nm than did wall layers excluding the middle lamellae. Vascular bundle sheaths generally were similar in digestion patterns and spectra to those of sclerenchyma. Parenchyma cells in internode 2, which were totally degradable, gave low absorbance. Parenchyma cell walls from internodes 5 and 7 were degraded except for the middle lamellae in cells nearest to the sclerenchyma; parenchyma cells nearest to the stem centre were totally degraded. Spectra of parenchyma wall regions that included middle lamellae were similar to the p-coumaroyl and feruloyl arabinoxylo-trisaccharides, and absorbance values were low compared with sclerenchyma and vascular walls. Results suggested that esteror ether-linked phenolic acids accounted for most of the UV absorption in young sclerenchyma and young and old parenchyma; lignin-like aromatics increased in older, poorly digested sclerenchyma as ester/ether-type compounds decreased. An estimation of the amount of ‘ferulic acid equivalents’ of the walls was made assuming all the absorbance at ? λ_max 320 nm was due to ferulic acid; older sclerenchyma walls had the highest values (160 mg g^?1 walls) and parenchyma walls the lowest (11 mg g^?1 walls).     

Forage quality variation among maize inbreds: Relationships of cell-wall composition and in-vitro degradability for stem internodes

Forty-five inbred maize (Zea mays L) lines were evaluated for genetic variation in stem cell-wall concentration, composition and degradability, and for relationships among cell-wall components and polysaccharide degradability. Cell-wall neutral sugars, uronic acids, Klason lignin, and ester- and ether-linked phenolic acids were measured on lower stem internode samples collected at the time of silking in 2 years. Twenty-four and 96 h in-vitro ruminal fermentations were used to determine the rapidly and potentially degradable cell-wall polysaccharide fractions, respectively. Genetic variation (P < 0.05) was found for all measures of cell-wall composition and many estimates of rapidly and potentially degradable cell-wall polysaccharide components. Inbred line means varied by 50–300% for most traits. Three brown midrib mutant inbred lines included in the study were not the lowest in lignin content nor did they exhibit the greatest cell-wall degradabilities in this population of inbred maize. Year of growth (environment) influenced (P < 0.05) cell-wall traits even though reproductive physiological maturity at sampling was similar in both years. Degradability of the cell-wall polysaccharide components were intercorrelated (P < 0.05) within the rapidly and potentially degradable fractions, but rate and extent of degradation of the cell-wall components were not correlated (P > 0.05), except for uronic acids. A multiple regression model of principal components (R² = 0.41, P < 0.05) indicated that cell-wall lignification and substitution of wall polymers with phenolic and uronic acids were negatively associated, and pectic substances were positively related with rapid polysaccharide degradation. Very little of the variation (R² = 0.15, P < 0.05) in potential cell-wall polysaccharide degradation could be explained by this multiple regression analysis. There is a large degree of genetic variation among current inbred maize lines for stem cell-wall quality traits, which should allow improvement of maize as a forage crop. Because of the complex matrix interactions in cell-wall organization, however, no single cell-wall component, or simple combination, can accurately predict degradability of maize cell walls.     

Phenolic acids released from bermudagrass (Cynodon dactylon) by sequential sodium hydroxide treatment in relation to biodegradation of cell types

Sections of solvent-extracted bermudagrass (Cynodon dactylon L Pers) leaf blades were treated sequentially with increasing concentrations of sodium hydroxide. The amounts of saponifiable phenolic acid monomers and cyclobutane dimers released and the digestibility of the treated blades (ie % dry weight loss) were determined. Leaf sections were examined by scanning electron microscopy for biodegradation of cell types and histochemically (light microscopy) for lignin after treatment with sodium hydroxide. Treatment with 0.1 m sodium hydroxide for 1 h resulted in only minor changes from untreated sections. However, this treatment for 24 h released 86% of the ferulic acid, 65% of the dimers, and c 50% of the p-coumaric acid. Digestibility was increased from 6.5% in the untreated control to 56.6%. Substantial loss of the slowly biodegradable tissues (ie epidermis and parenchyma bundle sheath) and partial biodegradation and disruption of the refractory tissues (ie sclerenchyma, xylem and mestome sheath) occurred; histochemical reactions for lignin were less intense after NaOH treatment. Treatment with 1 m sodium hydroxide for 24 h released 50% of the p-coumaric acid and the remainder of the alkali-extractable ferulic acid and dimers, increased digestibility to 72%, and increased biodegradation of mesophyll and phloem. Mestome sheath cell walls only gave a histochemical reaction for phenolics and the reaction was weak after 1 m NaOH treatment. Alkali treatment increased the biodegradation of all cell types, with lignified tissues reduced to single-cell fibres after 1 and 2 m treatments.     

Investigation of the ester- and ether-linked phenolic constituents of cell wall types of normal and brown midrib pearl millet using chemical isolation,microspectrophotometry and 13C NMR spectroscopy

The cell walls of rind, parenchyma and vascular bundle fractions of pearl millet (Pennisetum glaucum (L) R Br) were isolated from two brown midrib mutants and their normal (N) near-isogeneic line. The walls were sequentially treated with 1 M NaOH at 25°C for 20 h to determine ester-linked phenolic acids and then with 4 M NaOH at 170°C for 2 h to determine ether-linked phenolic constituents. The untreated walls and their residues resulting from each treatment were analyzed by microspectrophotometry and ¹³C NMR spectroscopy. The amount of ester-linked p-coumaric acid was determined by chemical analysis and found to be two to six times higher in the N line with no difference among lines in ferulic acid content. Ether-linked ferulic acid was about 30% higher in the rind in the N line and ether-linked p-coumaric acid was only slightly higher with the greatest difference found in the rind tissue. Microspectrophotometry of the untreated tissues showed absorption maxima at 232–238 nm. 288–292 nm and 312–324 nm. Treatment with 1 M NaOH generally reduced or eliminated the 312–324 nm absorption, with 4 M NaOH removing the remainder of the 288–292 nm absorption. ¹³C NMR confirmed these reductions of aromatic functionalities by alkali treatments. The combination of techniques provides excellent correlation of two types of spectral data with chemical identification and quantitation and establishes that bmr mutants have less ester-linked p-coumaric acid and less ether-linked ferulic acid, thus providing a better understanding of the factors contributing to biodegradability.     

Rates of degradation of plant cell walls measured with a commercial cellulase preparation

The relationship between the degradability, determined with a commercial cellulase preparation, of the cell walls of various plant parts of Italian ryegrass, maize and red clover can be expressed as Y = A - Be^?k₁^t-Cek₂^t, where Y = percentage of cell walls degraded, t = reaction time, k₁ and k₂ are rates of degradation, and A, B, and C are constants where A = B + C. Degradability of the cell walls of Italian ryegrass or maize could be predicted accurately from the absorbance of the filtrate at λ_max 282-288 or 310-324 nm. Treatment of cell walls of barley straw with 0.1 or 1M sodium hydroxide for 7 or 20 h degraded between 12 and 41% of the walls and led to the release of p-coumaric and ferulic acids, the amount increasing with concentration of alkali and treatment time; the less concentrated alkali released more ferulic than p-coumaric acid. Treatment with the cellulase preparation of the residues from alkali treatment showed that they were almost twice as degradable as the untreated walls.     

In vitro degradation of forage chicory (Cichorium intybus L.) by endopoly‐ galacturonase

BACKGROUND: Leaves of forage chicory break down rapidly in the rumen despite little or no rumination. Because chicory cell walls contain high concentrations of pectin, degradation of leaf midrib and leaf lamina tissues by pectinolytic enzymes was investigated. RESULTS: Treatment with endopolygalacturonase (endo‐PG) degraded fresh intact chicory leaves to particles of less than 1 mm in length and solubilised more than 70% of the dry matter within 16 h. Uronic acids were released more extensively than neutral monosaccharides. In similar treatments, 77% of white clover leaflets and 12% of perennial ryegrass leaf blades were solubilised or broken down to particles with a size of less than 1 mm. The degradation of pectic polysaccharides in chicory midribs was monitored by immunofluorescence labelling with monoclonal antibodies JIM5 and JIM7 which target partially methyl‐esterified epitopes of the homogalacturonan (HG) domain of pectin. Examination by fluorescence microscopy revealed that cell separation in the cortical parenchyma of chicory midrib following endo‐PG treatment was associated with loss of HG from the middle lamella, the corners of intercellular spaces and from the tricellular junctions. CONCLUSION: The results of the current study suggest that one of the main contributions to chicory breakdown in the rumen may be cell separation caused by degradation of HG by pectinolytic enzymes from rumen bacteria. Copyright © 2007 Society of Chemical Industry     

Effect of down-regulation of cinnamyl alcohol dehydrogenase on cell wall composition and on degradability of tobacco stems

The effect of down-regulation of tobacco cinnamyl alcohol dehydrogenase (CAD) on cell wall composition and degradability has been assessed. CAD activity was only 20, 16, 14 and 7%, relative to the controls, in four populations of plants (designated 40-1, 40-2, 48 and 50, respectively) transformed with CAD antisense mRNA. Cell wall residues of stem samples were analysed for polysaccharide composition, gravimetric and acetyl bromide lignins and lignin nitrobenzene oxidation products. In situ disappearance and cellulase solubility of both initial dry matter and CWR were determined. The populations of plants with depressed CAD activity showed no change in lignin content but some consistent changes in cell wall composition and digestibility were identified. The syringyl content of lignins decreased and the syringaldehyde to vanillin ratio (S/V) was consequently reduced. Dry matter degradability, as measured by both methods, was significantly improved in all CAD-depressed samples except for population 40-1, which was the least CAD-depressed. Increased in situ disappearance of cell wall (ISCWD) was found in all plants exhibiting more than 80% CAD down-regulation and was maximal (7 percentage units) in population 50 which had the greatest CAD depression. The rates of ISCWD increased slightly in some populations (40-2 and 50). The relationship between S/V and ISCWD was significant (R = -0·68) only in the samples from a selected population of mature, most depleted plants. Other modifications may therefore also contribute to the improvement in degradability. However the changes in lignin composition that were observed in CAD-depressed tobacco are largely similar to those seen in some maize and sorghum mutants with altered lignification and improved digestibility. These data therefore suggest that depressing CAD activity may be an effective method for improving digestibility in forage crops. © 1998 SCI.     

Visualizing the air-to-leaf transfer and within-leaf movement and distribution of phenanthrene: further studies utilizing two-photon excitation microscopy

Two-photon excitation microscopy (TPEM) was used to monitor the air-to-leaf transfer and within-leaf movement and distribution of phenanthrene in two plant species (maize and spinach) grown within a contaminated atmosphere. Phenanthrene was visualized within the leaf cuticle, epidermis, mesophyll, and vascular system of living maize and spinach plants. No detectable levels of phenanthrene were observed in the roots or stems of either species, suggesting phenanthrene entered the leaves only from the air. Phenanthrene was observed in both the abaxial and adaxial cuticles of both species. Particulate material (aerosols/dust) contaminated with phenanthrene was located at the surface of the cuticle and became encapsulated within the cuticularwaxes. Overtime, diffuse areas of phenanthrene formed within the adjacent cuticle. However, most of the visualized phenanthrene reaching the leaves arrived via gas-phase transfer. Phenanthrene was found within the wax plugs of stomata of both species and on the external surface of the stomatal pore, but not on the internal surface, or within the sub-stomatal cavity. Phenanthrene diffused through the cuticles of both species in 24-48 h, entering the epidermis to reside predominantly within the cell walls of maize (indicative of apoplastic transport) and the cellular cytoplasm of spinach (indicative of symplastic transport). Phenanthrene accumulated within the spinach cytoplasm where it concentrated into the vacuoles of the epidermal cells. Phenanthrene was not observed to accumulate in the cytoplasm of maize cells. Phenanthrene entered the internal mesophyll of both species, and was found within the mesophyll cell walls, at the surface of the chloroplasts, and within the cellular cytoplasm. Phenanthrene was observed within the xylem of maize following 12 days exposure. The cuticle and epidermis at the edges of spinach leaves had a systematically higher concentration of phenanthrene than the cuticle and epidermal cells at the center of the leaf. These results provide important new information about how such compounds enter, move, and distribute within leaves, and suggest that contemporary views of such processes based on data obtained from traditional analytical methods may need to be revised.     

Lignin composition is more important than content for maize stem cell wall degradation

BACKGROUND

The relationship between the chemical and molecular properties – in particular the (acid detergent) lignin (ADL) content and composition expressed as the ratio between syringyl and guaiacyl compounds (S:G ratio) – of maize stems and in vitro gas production was studied in order to determine which is more important in the degradability of maize stem cell walls in the rumen of ruminants. Different internodes from two contrasting maize cultivars (Ambrosini and Aastar) were harvested during the growing season.

RESULTS

The ADL content decreased with greater internode number within the stem, whereas the ADL content fluctuated during the season for both cultivars. The S:G ratio was lower in younger tissue (greater internode number or earlier harvest date) in both cultivars. For the gas produced between 3 and 20 h, representing the fermentation of cell walls in rumen fluid, a stronger correlation (R² = 0.80) was found with the S:G ratio than with the ADL content (R² = 0.68). The relationship between ADL content or S:G ratio and 72‐h gas production, representing total organic matter degradation, was weaker than that with gas produced between 3 and 20 h.

CONCLUSION

The S:G ratio plays a more dominant role than ADL content in maize stem cell wall degradation. © 2017 The Authors. Journal of The Science of Food and Agriculture published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.     

磷用量对烤烟烟叶发育和结构的影响

１９９２～１９９３年河南宝丰就磷用量对烤烟烟叶发育和叶片结构的影响进行了连续两年的观察研究，结果发现：在一定用量范围内，增施磷肥有促进叶肉细胞分裂，延迟胞间隙分化扩展，促进栅栏组织细胞伸长的作用。磷用量在５６．２５ｋｇ／ｈｍ２以内，增施磷肥既有提高定长叶的叶厚及棚栏组织厚度的作用，又有增加栅栏组织细胞密度，减小胞间隙面积（％）的作用，效果都很明显。磷用量５６．２５～３３７．５０ｋｇ／ｈｍ２，增施磷肥可明显提高定长叶的叶厚及栅栏组织厚度，但对棚栏组织细胞密度及胞间隙面积（％）的影响很小。磷用量超过３３７．５０ｋｇ／ｈｍ２，增施磷肥定长叶的叶厚、栅栏组织厚度及栅栏组织细胞密度降低，胞间隙面积（％）增加。定长叶栅栏组织厚度与叶厚的比值相当稳定，与磷用量的关系不大。