Apoplastic pH and monolignol addition rate effects on lignin formation and cell wall degradability in maize

Monolignol polymerization rate and apoplastic pH and may influence the formation of lignin and its interactions in cell walls. Primary maize walls were artificially lignified by gradual "end-wise" or rapid "bulk" polymerization of coniferyl alcohol at pH 4 or 5.5. Lignification efficiency was greatest for end-wise polymers at pH 5.5 (90-98%), intermediate for bulk polymers formed at either pH (54-82%), and lowest for end-wise polymers at pH 4 (41-53%). End-wise polymers had about 2.2-fold more ether inter-unit linkages and 70% fewer end-groups than bulk polymers. Low pH enhanced the formation of ether linkages in end-wise but not in bulk polymers. Differences in lignin structure did not influence the enzymatic degradability of cell walls, but lowering apoplastic pH from 5.5 to 4.0 during lignification reduced cell wall degradability by 25%. Further studies indicated this pH-dependent depression in degradability was related to cell wall cross-links formed via lignin quinone methide intermediates.     

In search of a maize ideotype for cell wall enzymatic degradability using histological and biochemical lignin characterization

Grass cell wall degradability is conventionally related to the lignin content and to the ferulic-mediated cross-linking of lignins to polysaccharides. To better understand the variations in degradability, 22 maize inbred lines were subjected to image analyses of Fasga- and M?ule-stained stem sections and to chemical analyses of lignins and p-hydroxycinnamic acids. For the first time, the nearness of biochemical and histological estimates of lignin levels was established. Combination of histological and biochemical traits could explain 89% of the variations for cell wall degradability and define a maize ideotype for cell wall degradability. In addition to a reduced lignin level, such an ideotype would contain lignins richer in syringyl than in guaiacyl units and preferentially localized in the cortical region rather than in the pith. Such enrichment in syringyl units would favor wall degradability in grasses, contrary to dicots, and could be related to the fact that grass syringyl units are noticeably p-coumaroylated. This might affect the interaction capabilities of lignins and polysaccharides.     

Impact of plant cell wall network on biodegradation in soil: Role of lignin composition and phenolic acids in roots from 16 maize genotypes

Residue quality is a key factor governing biodegradation and the fate of C in soil. Most investigations of relationships existing between crop residue quality and soil decomposition have been based on determining the relative proportions of soluble, cellulose, hemicellulose and lignin components. However, cell wall cohesion is increased by tight interconnections between polysaccharides and lignin that involve cross-linking agents (phenolic acids). The aim of this study was to determine the role of lignin composition and phenolic acids on short- to medium-term decomposition of maize roots in soil. Sixteen maize genotypes, presenting a range of chemical characteristics related to root lignin and phenolic acids, were used. The main components were characterized by Van Soest (VS) extraction and cell wall acid hydrolysis, and the non-condensed Syringyl and Guaicyl lignin monomers, esterified phenolic acids and etherified phenolic acids were determined. Maize roots were then incubated in soil under controlled conditions (15 °C, −80 kPa moisture) for 796 days. Results showed that VS extraction over-estimated the structural hemicellulose content and that VS lignin was more recalcitrant than Klason lignin. The tremendous effect of cell wall chemical characteristics was shown by marked variations (almost two-fold differences in C mineralization), between the 16 maize roots. Decomposition was controlled by soluble residue components in the short term whereas lignin and the interconnections between cell wall polymers were important in the long-term. Notably the cell wall domain rich in non-condensed lignin and esterified phenolic acids was prone to decomposition whereas the presence of etherified ferulic acids seemed to hamper cell wall decomposition.     

Methyl esterification divergently affects the degradability of pectic uronosyls in nonlignified and lignified maize cell walls

Nonlignified cell walls from Zea mays (L.) cell suspensions were incubated with and without pectin methylesterase (PME) and a portion were artificially lignified to assess how methyl esters influence the release of pectic uronosyls and total sugars from cell walls by fungal enzymes. Treatment with PME reduced uronosyl concentrations from 97 to 92 mg/g, reduced uronosyl methylation from 57% to 21%, and increased Klason lignin concentrations in artificially lignified cell walls from 99 to 116 mg/g. Although PME treatment slightly enhanced uronosyl release from nonlignified cell walls, it reduced uronosyl release from artificially lignified cell walls by 55% after 4 h and by 7% after 72 h of enzymatic hydrolysis. Pectin hydrolysis in PME treated cell walls was probably impaired by enhanced benzyl ester cross-linking of uronosyls to lignin via quinone methide intermediates. Variations in uronosyl methylation had little effect on the overall release of total sugars from cell walls.     

Variations in the cell wall composition of maize brown midrib mutants

Most studies published thus far on the four brown midrib (bm) mutants (bm1, bm2, bm3, and bm4) in maize (Zea mays L.) have focused on one or two individual mutants, and comparisons between studies have been difficult because of variation in genetic backgrounds, maturity, and source of tissue. Detailed analyses of the stalks of the four bm single mutants and a bm1-bm2 double mutant in a common genetic background (inbred A619) revealed structural and compositional changes in their isolated cell walls and lignins compared to the wild-type inbred. 2D-NMR revealed a significant presence of benzodioxane units in the bm3 isolated lignin. 1D (13)C NMR revealed increased aldehyde levels in the bm1 and bm1-bm2 mutants compared to the wild-type inbred. The bm3 and bm1-bm2 mutants contained less Klason lignin in the isolated cell walls. The bm1, bm3, and bm1-bm2 mutants contained approximately 50% less esterified p-coumaric acid with noticeably elevated levels of ferulate in the bm3 mutant. A difference among bm mutants in the solubility of p-coumaric acid-lignin complexes during cellulase enzyme treatment was also discovered, suggesting that the bm mutations might also differ in the structural organization of lignin.     

施用木质素对春玉米生长发育及产量的影响研究

试验研究施用木质素对春玉米生长发育及产量的影响结果表明 ,施用木质素可促进春玉米对N、P的吸收 ,提高肥料利用率 ,减少肥料污染和提高作物品质 ,有显著增产作用 ,且不同处理春玉米增产率均≥ 2 0 %。     

Impact of artificial root exudates on the bacterial community structure in bulk soil and maize rhizosphere

Bacterial densities, metabolic signatures and genetic structures were evaluated to measure the impact of soil enrichment of soluble organic carbon on the bacterial community structures. The exudates chosen were detected in natural maize exudates (glucose, fructose, saccharose, citric acid, lactic acid, succinic acid, alanine, serine and glutamic acid) and were used at a rate of 100 μg C g⁻¹ day⁻¹ for 14 days. Moreover two synthetic solutions with distinct carbon/nitrogen ratios (20.5 and 40.1), obtained by varying carboxylic and amino acids concentrations, were compared in order to evaluate the potential role of organic N availability. The in vitro experiment consisted of applying exudate solutions to bulk soil. In the case of the control, only distilled water was added. Both solutions significantly increased bacterial densities and modified the oxidation pattern of Biolog® GN2 plates with no effect of the C/N ratio on these two parameters. Genetic structure, measured by means of ribosomal intergenic spacer analysis (RISA), was also consistently modified by the organic amendments. N availability levels led to distinct genetic structures. In a second experiment, one of the previous exudate solutions (C/N 20.5) was applied to 15-day-old maize plants to determine the structural influence of exudates on the rhizosphere microbial community (in situ experiment). Bacterial densities were significantly increased, but to a lesser extent than had been found in the in vitro experiment. Metabolic potentials and RISA profiles were also significantly modified by the organic enrichment.     

Cross-linking of maize walls by ferulate dimerization and incorporation into lignin

Cross-linking of xylans and lignin by ferulates was investigated with primary maize walls acylated with 2% ferulate and with ferulate ethyl esters. Peroxidase-mediated coupling of wall ferulate and ethyl ferulate yielded mostly 8-coupled products, including three new dehydrodimers. Significant quantities of 5-5-coupled diferulate formed only within walls, suggesting that matrix effects influence dimer formation. Over 60% of wall ferulate dimerized upon H2O2 addition, suggesting that xylan feruloylation is highly regulated during wall biosynthesis to permit extensive dimer formation at the onset of lignification. During lignification, ferulate and 5-5-coupled diferulate copolymerized more rapidly and formed fewer ether-linked structures with coniferyl alcohol than 8-5-, 8-O-4-, and 8-8-coupled diferulates. The potential incorporation of most ferulates and diferulates into lignin exceeded 90%. As a result, xylans become extensively cross-linked by ferulate dimerization and incorporation to lignin, but only a small and variable proportion of these cross-links is measurable by solvolysis of lignified walls.     

The maize primary cell wall microfibril: a new model derived from direct visualization

Understanding the molecular architecture of the plant cell wall is critical to reducing the biomass recalcitrance problem, which currently impedes economic bioconversion processing. The parenchyma cell walls from field senesced, maize stem pith have been directly visualized without extraction processes using high-resolution atomic force microscopy (AFM). By imaging the cell wall inner surfaces from different cells and different faces of the same cell, we were able to map the native primary cell wall ultrastructures. Depending on the thickness of non-cellulosic deposition, the parallel-microfibrils appear in various morphologies ranging from clearly defined to completely embedded in the wall matrixes forming cell wall lamella. Macrofibrils were found to exist only on the uppermost layer of the native primary cell wall and appeared to be bundles of elementary fibrils. This novel observation led us to a new hypothesis for the cell wall fibrillar network and biosynthesis processes. Put concisely, a number of elementary fibrils are synthesized at one locus, that of the cellulose synthase complex (CelS), and coalesce into much larger macrofibrils. These macrofibrils eventually split at the ends to form parallel microfibrils with deposition of other cell wall components (i.e. hemicelluloses, pectin, etc.) also evident. On the basis of these AFM surface measurements and current supportive evidence from cell wall biophysics, biosynthesis, and genomics, we propose a new molecular model consisting of a 36-glucan-chain elementary fibril, in which the 36-glucan chains form both crystalline and subcrystalline structures. We also propose a modified model of CelS based on recently reported experimental evidence from plant cell wall biosynthesis.     

Identifying new lignin bioengineering targets: impact of epicatechin, quercetin glycoside, and gallate derivatives on the lignification and fermentation of maize cell walls

Apoplastic targeting of secondary metabolites compatible with monolignol polymerization may provide new avenues for designing lignins that are less inhibitory toward fiber fermentation. To identify suitable monolignol substitutes, primary maize cell walls were artificially lignified with normal monolignols plus various epicatechin, quercetin glycoside, and gallate derivatives added as 0 or 45% by weight of the precursor mixture. The flavonoids and gallates had variable effects on peroxidase activity, but all dropped lignification pH. Epigallocatechin gallate, epicatechin gallate, epicatechin vanillate, epigallocatechin, galloylhyperin, and pentagalloylglucose formed wall-bound lignin at moderate to high concentrations, and their incorporation increased 48 h in vitro ruminal fiber fermentability by 20-33% relative to lignified controls. By contrast, ethyl gallate and corilagin severely depressed lignification and increased 48 h fermentability by about 50%. The results suggest several flavonoid and gallate derivatives are promising lignin bioengineering targets for improving the inherent fermentability of nonpretreated cell walls.     

Moderate ferulate and diferulate levels do not impede maize cell wall degradation by human intestinal microbiota

The degradation of plant fiber by human gut microbiota could be restricted by xylan substitution and cross-linking by ferulate and diferulates, for example, by hindering the association of enzymes such as xylanases with their substrates. To test the influence of feruloylation on cell wall degradability by human intestinal microbiota, nonlignified primary cell walls from maize cell suspensions, containing various degrees of ferulate substitution and diferulate cross-linking, were incubated in nylon bags in vitro with human fecal microbiota. Degradation rates were determined gravimetrically, and the cell walls were analyzed for carbohydrates, ferulate monomers, dehydrodiferulates, dehydrotriferulates, and other minor phenolic constituents. Shifting cell wall concentrations of total ferulates from 1.5 to 15.8 mg/g and those of diferulates from 0.8 to 2.6 mg/g did not alter the release of carbohydrates or the overall degradation of cell walls. After 24 h of fermentation, the degradation of xylans and pectins exceeded 90%, whereas cellulose remained undegraded. The results indicate that low to moderate levels of ferulates and diferulates do not interfere with hydrolysis of nonlignified cell walls by human gut microbiota.     

不同种类精饲料中磷的瘤胃降解特性研究

测定了谷物籽实、豆类籽实及根茎三类共计15种饲料的磷含量,并应用尼龙袋法测定其在山羊瘤胃内的降解率。结果表明：三类饲料的磷含量存在明显差异,以豆类籽实最高,谷物籽实其次,根茎类最低。饲料种类间磷的瘤胃降解率差异极显著（P〈0.001）,谷物类、豆类和根茎类饲料中快速降解磷（A）分别以玉米（88.82%）、豌豆（92.66%）和红薯（94.69%）最高,而以大米、赤豆和木薯为最低。除大麦、大米和小米外,其他饲料的快速降解磷均在60%以上。除小麦外,慢速降解的磷（B）都低于40%。磷在瘤胃中的降解速率（C）都超过10%/h以上,仅大米、小米和土豆的慢速降解部分的降解速率低于10%/h。不同种类精饲料总的可降解磷（A＋B）都在80%以上。不同种类饲料磷的有效降解率都随外流速率的增大而下降,除大米和小米外,其他饲料磷的有效降解率都超过了80%。饲料中磷的含量与磷的有效降解率呈显著正相关关系,磷的降解速率与粗脂肪含量呈极显著正相关关系,淀粉含量则与磷的有效降解率呈显著负相关关系,磷的含量与粗蛋白含量间呈极显著正相关关系。上述结果显示,饲料中磷在瘤胃中绝大部分都可释放出来,故配制反刍动物日粮时必须考虑饲料原料中磷的含量及其有效降解率。     

降雨和蒸散对夏玉米灌溉需水量模型估算的影响

为揭示降雨和蒸散年际波动对作物灌溉需水量的影响机理,以华北平原南部地区夏玉米为研究对象,基于土壤水分概率密度函数建立灌溉需水量计算模型,分析了降雨、蒸散和灌溉需水量的年际波动特征,结合蒙特卡洛方法探讨了降雨和蒸散对灌溉需水量年际波动的贡献。结果表明:研究区夏玉米降雨参数年际波动显著,平均降雨量波动于4.958~25.003mm,变异系数为0.326;降雨频次波动于0.143~0.457 d-1,变异系数为0.170;平均降雨量和降雨频次均可采用Logistic分布描述:平均降雨量服从Logistic(11.273,2.022),降雨频次服从Logistic(0.318,0.029)。潜在蒸散量年际波动相对平稳,可采用对数正态分布描述:潜在蒸散量服从Log Normal(1.370,0.076)。灌溉需水量多年平均值为133.1mm,波动于8.1~381.8mm,变异系数为0.673,年际波动显著高于降雨和蒸散。平均降雨量对灌溉需水量年际波动的贡献率最大,其次为降雨频次,潜在蒸散量最小;在三者的共同作用下,灌溉需水量年际波动呈现出更大的不确定性。因此,在估算灌溉需水量时有必要对这种不确定性进行定量评估,针对不同降雨和蒸散条件制定合理的灌溉策略,为农业水资源管理和决策提供更可靠的科学依据。     

Inhomogeneities in the chemical structure of sugarcane bagasse lignin

Sequential treatments of dewaxed bagasse with distilled water, 0.5 M NaOH, 0.5, 1.0, 1.5, 2.0, and 3.0% H(2)O(2) at pH 11.5, and 2 M NaOH at 55 degrees C for 2 h solubilized 2.8, 52.5, 14.9, 3.3, 5.5, 5.0, 2.8, and 2.2% of the original lignin, respectively. The eight isolated lignin fractions were subjected to a comprehensive structural characterization by UV, FT-IR, and (1)H and (13)C NMR spectroscopies and thermal analysis. The nitrobenzene oxidation method was also applied to the in situ lignins. The seven lignin fractions, isolated successively with alkali and alkaline peroxide, were all SGH-type lignins, with a small amount of esterified p-coumaric acid and mainly etherified ferulic acid. No significant differences were found in the weight-average molecular weights (1680-2220 g/mol) of the seven alkali and alkaline peroxide dissolved lignins. However, the first four lignin fractions, isolated with 0.5 M NaOH and 0.5, 1.0, and 1.5% H(2)O(2) at pH 11.5, were rich in syringyl units and contained large amounts of noncondensed ether structures, whereas the last three lignin fractions, isolated sequentially with 2.0 and 3.0% H(2)O(2) at pH 11.5 and 2 M NaOH at 55 degrees C for 2 h, had a higher degree on condensation and were rich in guaiacyl lignins.     

Impact of genetics and environment on nutritional and metabolite components of maize grain

The Organization for Economic Co-operation and Development (OECD) recommends the measurement of specific plant components for compositional assessments of new biotechnology-derived crops. These components include proximates, nutrients, antinutrients, and certain crop-specific secondary metabolites. A considerable literature on the natural variability of these components in conventional and biotechnology-derived crops now exists. Yet the OECD consensus also suggests measurements of any metabolites that may be directly associated with a newly introduced trait. Therefore, steps have been initiated to assess natural variation in metabolites not typically included in the OECD consensus but which might reasonably be expected to be affected by new traits addressing, for example, nutritional enhancement or improved stress tolerance. The compositional study reported here extended across a diverse genetic range of maize hybrids derived from 48 inbreds crossed against two different testers. These were grown at three different, but geographically similar, locations in the United States. In addition to OECD analytes such as proximates, total amino acids and free fatty acids, the levels of free amino acids, sugars, organic acids, and selected stress metabolites in harvested grain were assessed. The major free amino acids identified were asparagine, aspartate, glutamate, and proline. The major sugars were sucrose, glucose, and fructose. The most predominant organic acid was citric acid, with only minor amounts of other organic acids detected. The impact of genetic background and location was assessed for all components. Overall, natural variation in free amino acids, sugars, and organic acids appeared to be markedly higher than that observed for the OECD analytes.     

气流粉碎对玉米淀粉结构及理化性质的影响

为研究气流粉碎对玉米淀粉结构及理化性质的影响,该文以普通玉米淀粉为原料,通过流化床气流粉碎处理,采用扫描电子显微镜、偏光显微镜、粒度分析仪、X-射线衍射仪、红外光谱仪、差示扫描量热仪、快速黏度分析仪等分析手段研究经微细化处理前后玉米淀粉颗粒形貌、晶体结构、热力学特性、糊化特性、溶解度和膨胀度、冻融稳定性、持水能力等结构及性质的变化。结果表明,微细化处理后,淀粉颗粒形变的不规则,粒径明显减小,中位径(D50)由14.37μm减小到5.25μm,偏光十字减少,相对结晶度由33.43%降低至15.46%,淀粉颗粒结晶结构被破坏,由多晶态向无定形态转变,粉碎过程淀粉无新的基团产生;热焓值、糊化温度均降低,热糊稳定性好;溶解度、膨胀度均升高,持水能力增加,冻融稳定性好,产生较好的热糊稳定性和冷糊力学稳定性,该研究为玉米淀粉的深度加工与应用提供了理论依据及技术支撑。     

三种肥力水平土壤施肥对玉米产量及经济效益的影响

以春玉米为供试材料,在山西省忻州市忻府区进行大田试验,设计配方施肥(TFR)、农民习惯施肥(FP)和对照(CK)3种施肥方式,研究高、中、低土壤肥力条件下,不同施肥方式对春玉米产量和经济效益、肥料利用率、农学效益的影响。连续两年大田试验结果表明,配方施肥与农民习惯施肥相比,高、中、低土壤肥力区玉米产量分别增加10.1%、13.2%和9.3%;与对照(CK)相比玉米产量分别增加33.7%、39.9%和47.6%。根据试验年份的物价计算,扣除肥料成本后,每公顷TFR比FP和CK玉米经济效益分别增加11.2%和9.2%。产量可持续指数表明,中肥力区增产效果最优。尿素的利用率为22.4%,普通过磷酸钙的利用率为9.9%,硫酸钾的利用率为21.2%。氮、磷、钾肥的农学效益分别为8.7、11.5和9.9 kg·kg~(-1)。配方施肥对春玉米增产、增收效果显著,可为山西省春玉米"两高一优"生产提供理论依据,为合理施肥提供数据参考。     

Impact of tillage on maize rooting in a Cambisol and Luvisol in Switzerland

Soil conditions under no-tillage (NT) are often unfavorable for the growth of maize roots in comparison to conventional tillage (CT). In 1997 and 1999, the impacts of tillage on the morphology and spatial distribution of maize (Zea mays L.) roots at anthesis were investigated in a 5-year field trial at two sites (loamy silt and sandy loam soils) in the Swiss midlands. Four soil cores, perpendicular to the maize row, were taken to a depth of 100 cm in each plot; the root length density (RLD), the mean root diameter (MD), and the relative length per diameter-class distribution (LDD) of the roots were determined.

Roots were longer and thinner in 1999 than in 1997. The RLD was significantly higher and the MD was smaller on the loamy silt than on the sandy loam. The RLD and MD decreased with the distance from the plant row. Most of the maize roots, about 80% of the total root length, were in the layer from 0 to 40 cm, with maximum values from 5 to 10 cm; the thickest roots were in the soil layer from 10 to 50 cm. Significant differences in RLD with increasing distance from the row of plants were found in the top 30 cm.

Averaged over the whole soil profile, RLD was higher and MD was smaller under CT than under NT. The impact of tillage on RLD and MD interacted with spatial factors and years. Within the soil profile, RLD was significantly higher under NT than under CT at a depth of 5 cm, whereas it was higher under CT than under NT below 10 cm. Below 50 cm, there was no difference in RLD between the tillage systems. In a horizontal direction, MD was consistently higher in the row and lower in the mid-row under NT than under CT.

Our results show that differences in maize root growth between tillage systems, which were reported in previous studies, persist until anthesis. The accumulation of maize roots near the soil surface in NT suggests that subsurface-banding of starter fertilizer is a more efficient way of applying fertilizer (particularly immobile nutrients such as phosphorus) compared with broadcasting in order to supply sufficient nutrients for NT maize.