Multi-site genetic modulation of monolignol biosynthesis suggests new routes for formation of syringyl lignin and wall-bound ferulic acid in alfalfa (Medicago sativa L.)

Genes encoding seven enzymes of the monolignol pathway were independently downregulated in alfalfa (Medicago sativa) using antisense and/or RNA interference. In each case, total flux into lignin was reduced, with the largest effects arising from the downregulation of earlier enzymes in the pathway. The downregulation of l-phenylalanine ammonia-lyase, 4-coumarate 3-hydroxylase, hydroxycinnamoyl CoA quinate/shikimate hydroxycinnamoyl transferase, ferulate 5-hydroxylase or caffeic acid 3-O-methyltransferase resulted in compositional changes in lignin and wall-bound hydroxycinnamic acids consistent with the current models of the monolignol pathway. However, downregulating caffeoyl CoA 3-O-methyltransferase neither reduced syringyl (S) lignin units nor wall-bound ferulate, inconsistent with a role for this enzyme in 3-O-methylation ofS monolignol precursors and hydroxycinnamic acids. Paradoxically, lignin composition differed in plants downregulated in either cinnamate 4-hydroxylase or phenylalanine ammonia-lyase. No changes in the levels of acylated flavonoids were observed in the various transgenic lines. The current model for monolignol and ferulate biosynthesis appears to be an over-simplification, at least in alfalfa, and additional enzymes may be needed for the 3-O-methylation reactions of S lignin and ferulate biosynthesis.     

Solubilization of lignin by the ruminal anaerobic fungus Neocallimastix patriciarum.

The ability of the ruminal anaerobic phycomycete Neocallimastix patriciarum to digest model lignin compounds and lignified structures in plant material was studied in batch culture. The fungus did not degrade or transform model lignin compounds that were representative of the predominant intermonomer linkages in lignin, nor did it solubilize acid detergent lignin that had been isolated from spear grass. In a stem fraction of sorghum, 33.6% of lignin was apparently solubilized by the fungus. Solubilization of ester- and either-linked phenolics accounted for 9.2% of the lignin released. The amounts of free phenolic acids detected in culture fluid were equivalent to the apparent loss of ester-linked phenolics from the sorghum substrate. However, the fungus was unable to cleave the ether bond in hydroxycinnamic acid bridges that cross-link lignin and polysaccharide. It is suggested that the majority of the solubilized lignin fraction was a lignin carbohydrate complex containing ether-linked hydroxycinnamic acids. The lignin carbohydrate complex was probably solubilized through dissolution of xylan in the lignin-xylan matrix rather than by lignin depolymerization.     

Chemistry and occurrence of hydroxycinnamate oligomers

Hydroxycinnamates such as ferulic acid, sinapic acid and p-coumaric acid ester-linked to plant cell wall polymers may act as cross-links between polysaccharides to each other, but also to proteins and lignin. Although sinapates and p-coumarates also form cell wall cross-links by the formation of radically or photochemically formed dimers, ferulate derivatives are the quantitatively most important cross-links in the plant cell wall. While the first radically generated ferulate dimer was already identified almost 40 years ago, the spectrum of known ferulate dimers was considerably broadened within the last 15 years. Higher ferulate oligomers were generated in model systems, but also isolated from plant materials. Different model systems using either free hydroxycinnamic acids or their esters are reviewed, highlighting a discussion of the relevance of these models for the plant cell wall. The first ferulate trimer from plant material was discovered in 2003 and seven dehydrotrimers of ferulic acid were isolated from maize bran since. Some of these trimers were also identified in other plant materials such as wheat and rye grains, corn stover, sugar beet and asparagus. Formation mechanisms of ferulate trimers and implications for the plant cell wall are discussed. Ferulate tetramers are the highest oligomers isolated from plant materials so far. These compounds can theoretically cross-link up to four polysaccharide chains, assuming all cross-links are formed intermolecularly. Formation of intramolecular versus intermolecular polysaccharide cross-links is a key question to be answered in the future if we want to judge properly the importance of hydroxycinnamate cross-links in the plant cell wall.     

Hot alkali-labile linkages in the walls of the forage grass Phalaris aquatica and Lolium perenne and their relation to in vitro wall digestibility

The factors affecting in vitro dry matter digestibility (IVDMD) of fully mature internodes of 150 lines of the forage grass, Phalaris aquatica, and internodes of 100 lines of perennial ryegrass (Lolium perenne), harvested just after anthesis, were investigated. The relationships between IVDMD and the contents of acetyl bromide lignin, and ester-ether linkages between lignin and wall polysaccharides, measured by hydroxycinnamic acids (HCAs) released by 4 M NaOH at 170 degrees C respectively, were determined. The regression analysis gave r(2)=0.05 and 0.03 for the relation between IVDMD and lignin content and r(2)=0.51 and 0.53 for the relation between IVDMD and the content of hot alkali-labile HCA (predominantly ferulic acid) for phalaris and ryegrass, respectively. These observations are interpreted in terms of the restricted accessibility of polysaccharide hydrolysing enzymes to their substrates in the forage cell walls by the covalent cross-linking of wall polymers through HCAs.     

Expression of a Trichoderma reesei β-1,4 endo-xylanase in tall fescue modifies cell wall structure and digestibility and elicits pathogen defence responses

An endo-xylanase from Trichoderma reesei (xyn2) has been expressed in tall fescue targeted to the vacuole, apoplast or Golgi, constitutively under the control of the rice actin promoter, and to the apoplast under the control of a senescence enhanced gene promoter. Constitutive xylanase expression in the vacuole, apoplast, and golgi, resulted in only a small number of plants with low enzyme activities and in reduced plant growth in apoplast, and golgi targeted plants. Constitutive expression in the apoplast also resulted in increased levels of cell wall bound hydroxycinnamic acid monomers and dimers, but no significant effect on cell wall xylose or arabinose content. In situ constitutive xylanase expression in the Golgi also resulted in increased ferulate dimers. However, senescence induced xylanase expression in the apoplast was considerably higher and did not affect plant growth or the level of monomeric hydroxycinnamic acids or lignin in the cell walls. These plants also showed increased levels of ferulate dimers, and decreased levels of xylose with increased levels of arabinose in their cell walls. While the release of cell wall hydroxycinnamic acids on self digestion was enhanced in these plants in the presence of exogenously applied ferulic acid esterase, changes in cell wall composition resulted in decreases in both tissue digestibility and cellulase mediated sugar release. In situ detection of H₂O₂ production mediated by ethylene release in leaves of plants expressing apoplast xylanase could be leading to increased dimerisation. High-level xylanase expression in the apoplast also resulted in necrotic lesions on the leaves. Together these results indicate that xylanase expression in tall fescue may be triggering plant defence responses analogous to foliar pathogen attack mediated by ethylene and H₂O₂.     

Relationships of fibre,lignin, and phenolics to in vitro fibre digestibility in three perennial grasses

Livestock performance can be improved by increasing the digestibility of feeds, one of the key elements of nutritional quality. Digestibility of feeds can be improved by breeding forage crops with modified cell-wall structure, increasing the potential availability of energy from the cell wall to rumen microbes and livestock. The objectives of this research were to identify interrelationships among lignin and phenolic components of the fibre fraction of three perennial grasses and to determine their influence on in vitro fibre digestibility. Differences in etherified and esterified ferulate and esterified p-coumarate among clones of three perennial grasses were generally repeatable across harvests. The concentration of neutral detergent fibre (NDF) and Klason lignin within the NDF fraction were the factors most limiting to 24-h in vitro digestibility, with NDF being the most important. Klason lignin and etherified ferulate were the factors most limiting to 96-h in vitro digestibility for all three species. Due to its positive correlation with NDF, selection for low etherified ferulate should be avoided in smooth bromegrass (Bromus inermis Leyss) and cockfsoot (Dactylis glomerata L.). It should be possible to select and breed for low concentrations of lignin to improve digestibility without decreasing NDF in these two species. However, in reed canarygrass (Phalaris arundinacea L.), both lignin and etherified ferulate were positively correlated with NDF, indicating that selection for increased digestibility should be based directly on some measure of in vitro digestibility to avoid the fitness problems associated with reduced NDF.     

Quantitative trait loci for cell-wall components in recombinant inbred lines of maize (Zea mays L.) I: stalk tissue

Maize silage is a significant energy source for animal production operations, and the efficiency of the conversion of forage into animal mass is an important consideration when selecting cultivars for use as feed. Fiber and lignin are negatively correlated with digestibility of feed, so the development of forage with reduced levels of these cell-wall components (CWCs) is desirable. While variability for fiber and lignin is present in maize germplasm, traditional selection has focused on the yield of the ear rather than the forage quality of the whole plant, and little information is available concerning the genetics of fiber and lignin. The objectives of this study were to map quantitative trait loci (QTLs) for fiber and lignin in the maize stalk and compare them with QTLs from other populations. Stalk samples were harvested from 191 recombinant inbred lines (RILs) of B73 (an inbred line with low-to-intermediate levels of CWCs) x De811 (an inbred line with high levels of CWCs) at two locations in 1998 and one in 1999 and assayed for neutral detergent fiber (NDF), acid detergent fiber (ADF), and acid detergent lignin (ADL). The QTLs were detected on nine chromosomes, mostly clustered in concordance with the high genetic correlations between NDF and ADF. Adjustment of NDF for ADF and ADF for ADL revealed that most of the variability for CWCs in this population is in ADF. Many of the QTLs detected in this study have also been detected in other populations, and several are linked to candidate genes for cellulose or starch biosynthesis. The genetic information obtained in this study should be useful to breeding efforts aimed at improving the quality of maize silage.     

Modification of esterified cell wall phenolics increases vulnerability of tall fescue to herbivory by the fall armyworm

Feruloylation of arabinoxylan in grass cell walls leads to cross-linked xylans. Such cross-linking appears to play a role in plant resistance to pathogens and insect herbivores. In this study, we investigated the effect of ferulate cross-linking on resistance to herbivory by fall armyworm (Spodoptera frugiperda) making use of genetically modified tall fescue [Schedonorus arundinaceus (Festuca arundinacea)] expressing a ferulic acid esterase gene. Mature leaves of these plants have significant reduced levels of cell wall ferulates and diferulates but no change in acid detergent lignin. These reduced levels of esterified cell wall ferulates in transgenic plants had a positive effect on all measures of armyworm larval performance examined. More larvae survived (89 vs. 57?%) and grew faster (pupated 2.1?days sooner) when fed transgenic leaves with reduced levels of cell wall ferulates, than when fed control tall fescue leaves where levels of cell wall ferulates were not altered. Overall, mortality, growth and food utilization were negatively associated with level of esterified cell wall ferulates and diferulates in leaves they were fed. This study is the first to use transgenic plants with modified level of cell wall esterified ferulates to test the role of feruloylation in plant resistance to insects. It is concluded that the accumulation of ferulates and the cross-linking of arabinoxylans via diferulate esters in the leaves of tall fescue underlies the physical barrier to insect herbivory. Reducing ferulate cross-linking in grass cell walls could increase susceptibility of these plants to insect folivores.     

The effects of sulphur supplementation on cellulose digestion in vitro and on nutrient digestion,nitrogen metabolism and rumen characteristics of lambs fed on good quality fescue and tropical star grass hays

Experiments were conducted in vitro and in vivo to determine the effects of sulphur (S) supplementation of a good quality fescue hay containing 0.27% total S and a tropical star grass hay containing 0.20% total S. Addition of S was on an isosulphurous basis of either sodium sulphate or D,L-methionine. Cellulose digestion in vitro was improved (P < 0.001) by the addition of 1% urea. Supplementation of forage with 0.05, 0.10 or 0.15% S from either sodium sulphate or methionine also stimulated cellulose digestion in vitro. There were no differences between S sources. The addition of 0.4 or 0.8% nitrate-nitrogen (nitrate-N) (potassium nitrate) depressed (P < 0.05) cellulose digestion in vitro of both hays. No effect of animal adaptation to nitrate was evident. Addition of S partially counteracted the depression in cellulose digestion due to nitrate. Trials were conducted in vivo in which 12 crossbred wether lambs (fescue experiment) or 12 crossbred intact male lambs (star grass experiment) were randomly assigned to one of three treatments: control (forage with no addition of S); forage plus 0.15% S as sodium sulphate; and forage plus 0.15% S as D,L-methionine. Lambs were housed in metabolism crates and each experiment was replicated twice. Dry matter intakes were highest for methionine-supplemented fescue and for S-supplemented star grass, regardless of S source. Dry matter digestibility tended to increase with S addition (fescue experiment) and was significantly higher for S-supplemented star grass. There was a significant increase (P < 0.05) in neutral detergent fibre (NDF) and acid detergent fibre (ADF) digestibility due to supplemental S, regardless of S source. Nitrogen retention, ammonia-N and ruminal volatile fatty acids were unaffected by S supplementation.     

Effects of Forage Quality and Cell Wall Constituents of Bermuda Grass on Biochemical Conversion to Ethanol

Bermuda grass is an attractive candidate as a feedstock for biofuel production because over four million hectares of Bermuda grass are already grown for forage in the Southern USA. Because both rumen digestion and biochemical conversion to ethanol depend upon enzymatic conversion of the cell wall polysaccharides into fermentable sugars, it is probable that grasses bred for increased forage quality would be more amenable for ethanol production. However, it is not known how variation in rumen digestibility and cell wall/fiber components correlates with efficiency of conversion to ethanol via fermentation. The objective of this research was to determine relationships between ethanol production evaluated by simultaneous saccharification and fermentation (SSF), 72-h in vitro ruminal dry matter digestibility (IVDMD), in vitro ruminal gas production after 24 and 96 h, and biomass composition for 50 genetically diverse Bermuda grass accessions. The Bermuda grass samples were subjected to standard 72-h IVDMD and forage fiber analyses. Also, in separate labs, gas production was measured in sealed volume-calibrated vials after 24 (NNG24) and 96 h (NNG96) of in vitro fermentation by ruminal fluid; ethanol and pentose sugar productions were measured from a bench-top SSF procedure; cell wall constituents were determined by the Uppsala Dietary Fiber Method; and total nitrogen, carbon, and ash concentrations were determined by using the LECO combustion method. Ethanol production was moderately correlated with IVDMD (r?=?0.55) and NNG96 (r?=?0.63) but highly correlated with NNG24 (r?=?0.93). Ethanol was negatively correlated with neutral detergent fiber (NDF; r?=??0.53) and pentose sugars (r?=??0.60), but not correlated with glucose content. Regression models indicated that NDF and cell wall pentose sugar concentrations had significant negative effects on ethanol production. Variation among entries for IVDMD was affected by variability of NDF, pentose sugar concentrations, and biomass nitrogen content. Variation in Klason lignin content had only minor negative impacts on ethanol production and IVDMD. Biochemical conversion efficiency of Bermuda grass by SSF can be best estimated by NNG24 but not by IVDMD.     

华南象草Pp4CL基因的克隆及其转基因烟草木质素含量分析

为探究华南象草(Pennisetum purpureumcv.Huanan)木质素合成关键酶基因的调控机制,通过同源克隆得到华南象草4-香豆酸:CoA连接酶基因(Pp4CL)的cDNA序列,长度为1 943bp,其中编码区序列1 662bp。Pp4CL蛋白由553个氨基酸组成,分子量为59.57kD,等电点为5.2,属于疏水性蛋白。该蛋白含有AMP结合结构域,属于AFD ClassⅠ超家族。在系统进化分析中,Pp4CL与At4CL1、Os4CL1遗传距离最近,聚为一支。Pp4CL氨基酸序列具有SSGTGLPKGV和GEICIRG等2个保守基序,是典型的植物4CL。构建原核表达载体pGEX-4CL,得到约88kD的Pp4CL-GST融合蛋白,为Pp4CL酶活性测定及Western免疫印迹分析奠定了基础。同时构建植物表达载体pBA-4CL,并通过叶盘法对烟草进行了遗传转化,得到3个转基因阳性株系(OX-9、OX-7、OX-4),它们中叶柄木质素总含量分别比非转基因植株(对照)提高了10.0%、16.2%和94.6%,茎秆基部节木质素总含量分别比对照提高了0.9%、4.0%和13.5%。研究结果表明,Pp4CL蛋白与木质素合成有关,过表达Pp4CL基因能够显著提高植株木质素含量。该研究结果为华南象草木质素改良工作打下了基础,同时也为深入开展牧草分子育种提供了依据。     

Forage selection by Royle's pika (Ochotona roylei) in the western Himalaya,India

Forage selection decisions of herbivores are often complex and dynamic; they are modulated by multiple cues, such as quality, accessibility and abundance of forage plants. To advance the understanding of plant–herbivore interactions, we explored foraging behavior of the alpine lagomorph Royle's pika (Ochotona roylei) in Kedarnath Wildlife Sanctuary, India. Pika bite counts on food plants were recorded through focal sampling in three permanently marked plots. Food plant abundance was recorded by traditional quadrat procedures; forage selection was estimated with Jacob's selection index. Multiple food-choice experiments were conducted to determine whether forage selection criteria would change with variation in food plant composition. We also analyzed leaf morphology and nutrient content in both major food plants and abundantly available non-food plants. Linear regression models were used to test competing hypotheses in order to identify factors governing forage selection. Royle's pika fed primarily on 17 plant species and each forage selection decision was positively modulated by leaf area and negatively modulated by contents of avoided substances (neutral detergent fiber, acid detergent fiber, acid detergent lignin and tannin) in food plants. Furthermore, significance of the interaction term “leaf size × avoided substance” indicates that plants with large leaves were selected only when they had low avoided substance content. The forage selection criteria did not differ between field and laboratory experiments. The parameter estimates of best fit models indicate that the influence of leaf size or amount of avoided substance on pika forage selection was modulated by the magnitude of predation risk.     

Evaluation of eastern gamagrass as dual-purpose complementary bioenergy and forage feedstock to switchgrass

Switchgrass (SG) is considered a model bioenergy crop and a warm-season perennial grass (WSPG) that traditionally served as forage feedstock in the United States. To avoid the sole dependence on SG for bioenergy production, evaluation of other crops to diversify the pool of feedstock is needed. We conducted a 3-year field experiment evaluating eastern gamagrass (GG), another WSPG, as complementary feedstock to SG in one- and two-cut systems, with or without intercropping with crimson clover or hairy vetch, and under different nitrogen (N) application rates. Our results showed that GG generally produced lower biomass (by 29.5%), theoretical ethanol potential (TEP, by 2.8%), and theoretical ethanol yield (TEY, by 32.9%) than corresponding SG under the same conditions. However, forage quality measures, namely acid detergent fiber (ADF), crude protein (CP), and elements P, K, Ca, and Mg were significantly higher in GG than those in SG. Nitrogen fertilizer significantly enhanced biomass (by 1.54 Mg ha⁻¹), lignin content (by 2.10 g kg⁻¹), and TEY (787.12 L ha⁻¹) in the WSPGs compared to unfertilized treatments. Intercropping with crimson clover or hairy vetch did not significantly increase biomass of the WSPGs, or TEP and TEY in unfertilized plots. This study demonstrated that GG can serve as a complementary crop to SG and could be used as a dual-purpose crop for bioenergy and forage feedstock in farmers' rotations.     

Ferulate–coniferyl alcohol cross-coupled products formed by radical coupling reactions

Radical coupling reactions between ethyl ferulate (Et-FA), a simple model for feruloyl polysaccharides in planta, and coniferyl alcohol (CA), a monolignol, were studied in order to better understand the polymer cross-coupling interactions among polysaccharides and monolignols or lignin, mediated by ferulate (FA), in plant cell walls. Cross-coupled FA/CA dimers produced in an aqueous buffer (pH 5.0) containing peroxidase/hydrogen peroxide were isolated and characterized by NMR. The total coupling products were characterized by 2D ¹³C–¹H correlation (HSQC) NMR spectroscopy and GC–MS. Results from this study showed that ferulate readily cross-couples with coniferyl alcohol through free radical coupling mechanisms producing a series of cross-coupled FA/CA dimers with β-O-4-, β-5-/8-5-, and 8-β-linkages; the syntheses and isolation of β-5- and 8-5-cross-coupled dimers are reported here. The transformation from 8-β-coupled FA/CA hydroxyl esters into lactones through intramolecular transesterification is demonstrated for the first time and mechanisms behind these transformations are discussed. The finding of both β-5- and 8-5-cross-coupled dimers in this study suggests that analogs of both may be present in plant cell walls. Finally it is suggested that ferulates in plants indeed react with monolignols through free radical mechanisms producing a more diverse array of cross-coupled dimers than previously reported.     

Genetic mapping and analysis of quantitative trait loci affecting fiber and lignin content in maize

Plant cell walls of forage provide a major source of energy for ruminant animals. Digestion of cell walls is limited by the presence of lignin, therefore the improving the digestibility of forages by reducing lignin content is a major goal in forage crop breeding programs. A recombinant inbred line maize population was used to map quantitative trait loci (QTL) for neutral detergent fiber (NDF), acid detergent fiber (ADF), and acid detergent lignin (ADL) of leaf-sheath and stalk tissues. All traits were positively genetically correlated. The larger genetic correlations were between NDF and ADF in sheaths (r = 0.84), NDF and ADF (r = 0.96), ADF and ADL (r = 0.83), and NDF and ADL (r = 0.76) in stalks. Twelve QTL were detected for NDF and 11 QTL for ADF in leaf-sheaths. Eight QTL detected for both traits were defined by the same or linked marker loci. Eight QTL were associated with leaf-sheath ADL. Eleven QTL were detected for NDF and ADF, and 12 QTL for ADL in stalks. Nine of eleven QTL detected for both NDF and ADF in stalks coincided in their genomic position. A high proportion of QTL detected for these traits had the same parental effects and genomic locations, suggesting that it is only necessary to select on one fiber component (NDF or ADF) to improve digestibility. Favorable correlated responses of unselected fiber components are expected due to coincident genomic locations of QTL and the high genetic correlation between fiber components. Several QTL detected in this study coincided in their positions with putative cellulose synthase genes from maize.     

Characterization of novel Brown midrib 6 mutations affecting lignin biosynthesis in sorghum

The presence of lignin reduces the quality of lignocellulosic biomass for forage materials and feedstock for biofuels. In C4 grasses,the brown midrib phenotype has been linked to mutations to genes in the monolignol biosynthesis pathway. For example,the Bmr6 gene in sorghum(Sorghum bicolor) has been previously shown to encode cinnamyl alcohol dehydrogenase(CAD),which catalyzes the final step of the monolignol biosynthesis pathway. Mutations in this gene have been shown to reduce the abundance of lignin,enhance digestibility,and improve saccharification efficiencies and ethanol yields. Nine sorghum lines harboring five different bmr6 alleles were identified in an EMS-mutagenized TILLING population. DNA sequencing of Bmr6 revealed that the majority of the mutations impacted evolutionarily conserved amino acids while three-dimensional structural modeling predicted that all of these alleles interfered with the enzyme's ability to bind with its NADPH cofactor. All of the new alleles reduced in vitro CAD activity levels and enhanced glucose yields following saccharification. Further,many of these lines were associated with higher reductions in acid detergent lignin compared to lines harboring the previously characterized bmr6-ref allele. These bmr6 lines represent new breeding tools for manipulating biomass composition to enhance forage and feedstock quality.     

Composition of cell wall phenolics and polysaccharides of the potential bioenergy crop –Miscanthus

The composition and concentrations of cell wall polysaccharides and phenolic compounds were analyzed in mature stems of several Miscanthus genotypes, in comparison with switchgrass and reed (Arundo donax), and biomass characteristics were correlated with cell wall saccharification efficiency. The highest cellulose content was found in cell walls of M. sinensis‘Grosse Fontaine’ (55%) and in A. donax (47%) and lowest (about 32%) in M. sinensis‘Adagio’. There was little variation in lignin contents across M. sinensis samples (all about 22–24% of cell wall), however, Miscanthus×giganteus (M × g) cell walls contained about 28% lignin, reed – 23% and switchgrass – 26%. The highest ratios of cellulose/lignin and cellulose/xylan were in M. sinensis‘Grosse Fontaine’ across all samples tested. About the same total content of ester‐bound phenolics was found in different Miscanthus genotypes (23–27 μg/mg cell wall), while reed cell walls contained 17 μg/mg cell wall and switchgrass contained a lower amount of ester‐bound phenolics, about 15 μg/mg cell wall. Coumaric acid was a major phenolic compound ester‐bound to cell walls in plants analyzed and the ratio of coumaric acid/ferulic acid varied from 2.1 to 4.3, with the highest ratio being in M × g samples. Concentration of ether‐bound hydroxycinnamic acids varied greatly (about two‐three‐fold) within Miscanthus genotypes and was also the highest in M × g cell walls, but at a concentration lower than ester‐bound hydroxycinnamic acids. We identified four different forms of diferulic acid esters bound to Miscanthus cell walls and their concentration and proportion varied in genotypes analyzed with the 5‐5‐coupled dimer being the predominant type of diferulate in most samples tested. The contents of lignin and ether‐bound phenolics in the cell wall were the major determinants of the biomass degradation caused by enzymatic hydrolysis.     

Orientation nouvelle du métabolisme des acides hydroxycinnamiques dans les fruits de tomates blessés (Lycopersicon esculentum)

A change in the metabolism of hydroxycinnamic acids in wounded tomato fruits (Lycopersicon esculentum) .
Healing of lesions in tomato fruits (Lycopersicon esculentum Mill. var. cerasiforme ) is partly due to lignification of cells bordering the wounded zones. The pericarp of healthy fruits contains a high level of hydroxycinnamic derivatives but never shows lignification. Thus, the reaction of the fruit to wounding seems to be a change in the metabolism, leading to the formation of monomeric units of which lignins are constituted. Hydroxycinnamate:CoA ligase (EC 6.2.1.12; CL) and O-methyltransferase (EC 2.1.1.6; OMT) appear to play an important role in this change. In wounded fruits CL acts preferentially on p-coumarate and ferulate as compared to caffeate, and OMT is particularly active with 5-OH ferulate as substrate. These changes lead to the formation of p-coumaroyl CoA, feruloyl CoA and sinapate, which are incorporated into lignin. Phenylalanine ammonialyase (EC 4.3.1.5) and glucosyltransferase activities increase greatly after wounding, whereas the activity of hydroxycinnamoyl-CoA:quinate hydroxycinnamoyl transferase decreases. These data complement those previously reported on peroxidases and suggest that, after the increase of enzyme activities, monomeric units are formed and then polymerized by some peroxidases specific for lignification.     

Hydroxycinnamates in lignification

Hydroxycinnamates incorporate into lignins by various mechanisms. The polysaccharide esters of ferulate, in particular, and the range of dehydrodiferulates and higher oligomers in grasses, participate in free-radical (cross-)coupling reactions during lignification to become integrally bound into the lignin polymer, resulting in extensive cross-linking between lignins and polysaccharides. Monolignol-hydroxycinnamate (primarily monolignol-p-coumarate) conjugates are primary building blocks for lignins, again in grasses (but analogously with monolignol acetates and p-hydroxybenzoates in other plants); radical coupling reactions of the monolignol moiety of the conjugate result in lignins with pendant p-coumarate units acylating a variety of lignin structures. Recent evidence suggests that even the hydroxycinnamic acids themselves can be monomers in lignification in wild-type and transgenic plants, undergoing radical cross-coupling reactions to incorporate into the polymer with interesting consequences. The compatibility of ferulate, in particular, with lignification suggests that plants able to utilize monolignol-ferulate conjugates in their primary monomer supply will be particularly well suited for subsequent chemical delignification, potentially improving processes for biomass conversion to biofuels, and for chemical pulping.     

Ethanol production potential of sweet sorghum assessed using forage fiber analysis procedures

Sweet sorghum (Sorghum bicolor (L.) Moench) is widely recognized as a highly promising biomass energy crop with particular potential to complement sugarcane production in diversified cropping systems. Agronomic assessments have led to identification of four cultivars well suited for such sugarcane‐based production systems in southern Louisiana. Sweet sorghum biofuel production systems are currently being developed, and research producing large sample numbers requiring ethanol yield assessment is anticipated. Fiber analysis approaches developed for forage evaluation appear to be useful for screening such large numbers of samples for relative ethanol yield. Chemical composition, forage fiber characteristics, digestibility, and ethanol production of sweet sorghum bagasse from the four cultivars were assessed. Measures of detergent fiber, lignin, and digestibility were highly correlated with ethanol production (P < 0.01). The best linear regression models accounted for about 80% of the variation among cultivars in ethanol production. Bagasse from the cultivar Dale produced more ethanol per gram of material than any of the other cultivars. This superior ethanol production was apparently associated with less lignin in stems of Dale. Forage evaluation measures including detergent fiber analyses, in vitro digestibility, and an in vitro gas production technique successfully identified the cultivar superior in ethanol yield indicating their usefulness for screening sweet sorghum samples for potential ethanol production in research programs generating large sample numbers from evaluations of germ plasm or agronomic treatments. These screening procedures reduce time and expense of alternatives such as hexose sugar assessment for calculating theoretical ethanol yield.