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Lignins definition, potential applications, (macro)molecular structures and properties, analytical characterisations and natural versus induced variability are reviewed with reference to both the biological diversity of lignification patterns in ecotypes, mutants and transgenic plants and the levels of organisation of the lignins polymeric networks. A discrimination between a common primary, guaiacyl type metabolism and a more specific secondary, syringyl type is suggested as a base of this variability and properties.

Absorbance at 280 nm was used to determine lignin concentrations in solutions of cell walls from winter wheat whole-crop silage, stems, and straw. Three different cell wall preparations (hot water−organic solvent fiber, ethanol−benzene residue, neutral detergent fiber) were prepared and dissolved in either HCl−triethylene glycol or acetyl bromide. Three phenolic standard solutions were used to calculate lignin concentrations in the wheat materials from absorbance readings: mixtures of phenolic monomers based on aldehydes (HIGUCHI), aldehydes and acids (REEVES), and washed Indulin (WIND). Gravimetric Klason lignin determination on the cell wall preparations consistently gave higher values than spectrophotometric lignin analysis. Material recovered as cell wall was slightly greater for hot water−organic solvent fiber than for neutral detergent fiber and was lowest for ethanol−benzene residue, probably due to partial dissolution of cell wall components with the latter procedure. Acetyl bromide shifted UV sp...

Internodes of maize (Zea mays L, Co125), harvested 5 days after anthesis, were sectioned into five equal parts and samples of sclerenchyma and parenchyma cells mechanically isolated from each section. Phenolic acids and syringyl and guaiacyl degradation products of lignin were released from the walls of the two cell types by microwave digestion with 4 M NaOH. Aryl ether bonded units were selectively released by thioacidolysis. Total phenolic content of cell walls from the youngest (basal) sections were approximately two-thirds of those of the oldest, topmost sections (parenchyma 70·8–99·0 and sclerenchyma 72·5–114·1 mg g-1) indicating that the process of lignification was already well advanced amongst most of the cell walls of the youngest section. The total phenolic content was marginally, but significantly, greater (P

Contrairement a beaucoup d'arbres feuillus, le bois de reaction des Eucalyptus n'est pas caracterise par les fibres G. Il peut cependant etre caracterise par ses deformations de maturation. La mesure des deformations residuelles longitudinales de maturation (DRLIVI) par relaxation de contraintes en peripherie des troncs a permis un classement continu et quantitatif d'echantillons de bois de clones crEucaetus hybrides du Congo. Ce type de mesure permet d'identifier mecaniquement le bois de tension. Les relations entre structure et proprietes mecaniques de ces bois ont ete etudiees par une analyse ultrastructurale et chimique des echantillons, en particulier par l'examen de la composition monomerique des lignines par thioacidolyse. Les resultats presentes ici montrent qu'il existe : i) une forte variabilite des DRLM avec des valeurs elevees, mome sur nos arbres peu penches et peu excentres, et malgre l'absence de fibres G ; ii) une correlation negative entre le niveau de DRLM, le taux de lignines et l'angle des microfibrilles de cellulose, iii) une correlation positive entre le niveau de DRLM et le rapport des taux de monomeres de lignines: unites syringyles 1 unites guaiacyles. La signification de ces correlations est discutee (causalite mecanique directe ou correlations plus complexes entre variables structurales). (Resume d'auteur)

The rate of oxidation of spruce milled wood lignin by Phanerochaete chrysosporium was investigated with precipitated lignin as well as lignin finely dispersed in water (colloidal lignin). H2O2 consumption rates in the course of lignin oxidation in the presence of purified lignin peroxidase were much higher with colloidal lignin compared with precipitated lignin. Characterization of reaction products and molecular-size distribution confirms that reaction rate of lignin peroxidase with 14C-lignin is strongly dependent on the physical state of lignin. The lignin peroxidase catalyse mainly repolymerization of colloidal lignin. However, in the presence of veratryl alcohol, both polymerization and depolymerization were observed.

The structure and surface properties of spread layers of lignins at the air/water interface have been studied by neutron reflectivity, spectroscopic ellipsometry, and static and dynamic tensiometry. The layers hold 70% water, and the surface concentration of lignin measured by neutron reflectivity is less than the amount deposited. When the spread amount increases from 1 to 16 mg m-2, 65−12.5% of the deposited lignin is recovered at the interface. The absolute value of the Brewster ellipticity decreases slowly after spreading and tends toward quasi-equilibrium after 30 h, a fact which could be explained by a slow desorption from the interfacial layer to the bulk. After a compression of the interfacial layers, the surface pressure and the Brewster ellipticity exhibit a strong relaxation due, at least in part, to a desorption. However, the diffusion of lignin molecules from the layer to the substrate is limited because at equilibrium the neutron reflectivity and ellipsometry data show that a significant lay...

Brown-midrib (bm) mutants of maize have modified lignin of reddish-brown colour. Although four independent bm loci are known, only one of the mutant genes has been previously identified. We report here that maize bm1, one of the less characterised mutants, shows severely reduced CAD activity in lignified tissues, resulting in the production of a modified lignin. Both the total lignin content and the structure of the polymer are altered by the mutation. We further describe the isolation and characterisation of the maize CAD cDNA and mapping of the CAD gene. CAD maps very closely to the known location of bm1 and co-segregates with the bm1 locus in two independent recombinant inbred populations. These data strongly support the premise that maize bm1 directly affects expression of the CAD gene.

In addition to morphological factors (height of the plant, proportion of stems), alfalfa quality is related to several biochemical factors, especially the content and monomeric composition of the cell wall components. This work was aimed at studying internode development in relation to the chemical composition and fractionation of cell walls. Analyses were performed on the fourth apical internodes (elongating), the two following ones (onset of cambial activity), and bottom internodes (mature). Deposition of guaiacyl type lignin occurred in the pectin rich cell walls of apical internodes. The onset of cambial activity corresponded to cell wall accumulation of syringyl-guaiacyl lignin, xylans and/or glucuronoxylans, and cellulose. Such events were related to the thickening of secondary cell walls which proportion increased in mature internodes. Chemical fractionation of the cell walls allowed the release of a high content of water soluble pectins from apical internodes, whereas alkalis were more efficient in extracting heteroxylans from bottom internodes. A partial release of lignin from the cell walls also occurred during the extraction steps. Lignin solubilization was enhanced by the cleavage of labile-ether lignin structures and appeared closely related to the extent of internode differentiation along the stem. Data gained from chemical fractionations evidenced that lignin-xylan-pectic complexes accumulated progressively in secondary wall rich tissues.

Peroxidases and laccases are key enzymes in the lignin biodegradation process. They oxidize phenolic and non-phenolic lignin model compounds into their phenoxy and cation radicals, respectively. Further non-enzymatic evolution lead then to various C-C and ether bond cleavages. Nevertheless, almost no information on the structural alterations undergone in vitro or in situ by lignin after enzymatic catalysis is available. We report here on the molecular structure of lignin oxidized by various (per)oxidasic systems. The oxidizability of phenolic and non-phenolic structures of the guaiacyl and syringyl type in the lignin network will be discussed as well as the modification of the macromolecular properties of the polymer oxidized in situ or in isolated state.

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In the present study, we have performed chemical investigations of the stem cell walls during internode maturation in order to study the growth dynamics of alfalfa and the deposition of the main cell wall components (polysaccharides and lignins). Internode cell walls were analysed by chemical fractionation using a mild delignification step aiming at sequential removal of polysaccharides and lignins. Delignification facilitated the subsequent removal of the xylose-rich polysaccharides by NaOH extraction as previously shown. This trend was more pronounced in the case of older internodes which have a larger proportion of secondary tissues containing syringyl type lignins in contrast to younger ones which are mainly composed of primary tissues containing guaiacyl type lignins and pectin rich cell walls.

Cinnamyl alcohol dehydrogenase (CAD) catalyzes the last step in the biosynthesis of the lignin precursors, the monolignols. We have down-regulated CAD in transgenic poplar (Populus tremula X Populus alba) by both antisense and co-suppression strategies. Several antisense and sense CAD transgenic poplars had an approximately 70% reduced CAD activity that was associated with a red coloration of the xylem tissue. Neither the lignin amount nor the lignin monomeric composition (syringyl/guaiacyl) were significantly modified. However, phloroglucinol-HCl staining was different in the down-regulated CAD plants, suggesting changes in the number of aldehyde units in the lignin. Furthermore, the reactivity of the cell wall toward alkali treatment was altered: a lower amount of lignin was found in the insoluble, saponified residue and more lignin could be precipitated from the soluble alkali fraction. Moreover, large amounts of phenolic compounds, vanillin and especially syringaldehyde, were detected in the soluble alkali fraction of the CAD down-regulated poplars. Alkaline pulping experiments on 3-month-old trees showed a reduction of the kappa number without affecting the degree of cellulose degradation. These results indicate that reducing the CAD activity in trees might be a valuable strategy to optimize certain processes of the wood industry, especially those of the pulp and paper industry.

The removal of lignin in paper manufacture is a toxic and energy-requiring process. For the paper industry and for the environment, it would be very beneficial to process trees with less lignin or with lignin that is more easily ex tractable. To achieve this goal, we are down-regulating the activity of a number of lignin biosynthesis enzymes in poplar by genetic engineering and studying their role in determining the quantity and quality of lignin. Here, our recent results obtained in this field are summarized with emphasis on bispecific caffeic acid/5-OH-ferulic acid-O-methyltransferase, cinnamoyl-CoA-reductase, caffeoyl-CoA-O-methyltransferase, and peroxidase.

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Cinnamyl alcohol dehydrogenase (CAD) catalyses the last step in the biosynthesis of the lignin precursors, which is the conversion of cinnamaldehydes into cinnamyl alcohols. A poplar (P. trichocarpa x P. deltoides)CAD cDNA was introduced in sense and in antisense orientation into P. tremula x P. alba via an Agrobacterium- mediated transformation. The CAD activity was reduced by 70% in the xylem tissue of three antisense and two co-suppressed lines. A red coloration of the xylem was detected in all poplar lines with a residual CAD activity of less than 60 %. The lignin content and the lignin composition (syringyl/guaiacyl) were similar in co-suppressed, antisense CAD and control lines. However, chemical properties of the cell wall were different. First, a phloroglucinol staining showed a different coloration in the xylem of the down-regulated CAD poplars, being red-brown as compared to the typical pink staining of the control xylem. Second, after NaOH treatment, lignin could be precipitated by acidification of the alkali-soluble fraction of the cell wall of the red poplars but not of that of the white poplars. A spectral characterisation of the alkali fraction from red poplars showed an increased level of vanillin and syringaldehyde. Third, pulping experiments showed less residual lignin in the pulp of CAD down-regulated poplars.

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The effects of the maize brown-midrib genes bm3 and bm1 on feeding value and agronomic traits were investigated by animal studies and biochemical approaches. When sheep were fed bm3 silage, an increase in digestibility was observed, equal to 2.4 points for digestibility of organic matter (DOM), and 8.1 points for digestibility of crude fiber (DCF). Phenotypic variation was reduced for all observed traits of bm3 hybrids. This allowed the assumption that the bm3 gene acted by levelling to a similar value of almost 74% DOM, quite independently of the original value of the normal counterpart. The bm1 hybrids were intermediate between normal and bm3 ones for DOM, DCF and intake, but the dry matter yield was not reduced for bm1 hybrids. From experiments with young bulls, feed efficiency of INRA260 bm1 was not significantly improved, compared with normal INRA260, but INRA260 bm3 was a lot more efficient. Despite its lower adverse effect on agronomic characteristics of hybrids, the bm1 allele did not appear to be of any interest in improving the silage maize feed efficiency. Variations for lignin content due to the bm3 gene was similar for the 3 hybrids studied, despite their variation for susceptibility to root and stalk lodging. Ratios and content of alkali-labile hydroxycinnamic acids behaved similarly for the 3 hybrids, with a low yield of para-coumaric acid. Structural studies of lignin, after thioacidolysis, strengthened the results previously obtained, with a clear decrease of syringyl units, and the occurrence of the 5-hydroxyguaiacyl residue. The lignin of bm3 genotypes also appeared as a more condensed polymer than that of the normal types. The decrease of lignin content was observed in only 1 bm1 hybrid and appeared the same between normal and bm1 hybrids as between normal and bm3 hybrids. The lower yield of para-coumaric acid, and the equal yield of ferulic acid after alkaline hydrolysis of bm1 material were in good agreement with previous work. After thioacidolysis, the release of monomeric syringyl units was similar between bm1 and bm3, about 30% of the normal counterpart. However, it was very different for guaiacyl units, with a large decrease of the release of these units from the bm1 hybrid. The ratio between syringyl and guaiacyl units was about 0.3 for bm3 hybrids and about 1.3 for the bm1 hybrid. The lignin of this bm1 hybrid appeared as a very condensed polymer compared with the normal type. A large variation for digestibility was also found among normal hybrids. However, inbred lines inducing high digestibility often included unfavorable agronomic traits, such as poor yield, susceptibility to lodging or stalk rot. Second or third cycle lines following pedigree breeding might combine all traits, even if stalk standability and stalk digestibility are partly antagonistic. This method may be considered as easier than the bm3 method, but at present, the 2 ways are probably complementary, and worth investigating for improving silage digestibility, and simultaneously increasing knowledge on silage maize digestibility., Les effets des gènes brown-midrib bm1 et bm3 sur la valeur alimentaire et les caractéristiques agronomiques d’hybrides de maïs ont été étudiés à partir d’essais sur animaux et de mesures de composition biochimique de la lignine. Sur moutons, les hybrides bm3 conduisent à une amélioration moyenne de la digestibilité de la matière organique (DOM) voisine de 2,4 et de celle de la cellulose brute (DCF) voisine de 8,1 points. La variabilité phénotypique est nettement réduite entre hybrides bm3, comparée à celle observée pour les quasi isogéniques normaux, pour la quasi-totalité des caractères étudiés. En particulier, il semble que la présence du gène bm3 conduise à augmenter la DOM des hybrides à une valeur proche de 74%, quel que soit le niveau de digestibilité de l’hybride normal de départ. Les hybrides bm1 se situent de façon intermédiaire entre les formes normales et bm3, sauf pour la productivité en biomasse qui est équivalente à celle des normaux. Mais des essais de croissance comparée de taurillons nourris avec des ensilages de maïs INRA260, INRA260 bm1 et INRA260 bm3 montrent que la forme bm1 ne permet pas, contrairement à la forme bm3, une amélioration notable des performances animales. La réduction de teneur en lignine a été semblable pour les 3 hybrides bm3 étudiés, alors que ces hybrides présentaient des différences importantes de sensibilité à la verse ou à la casse. Les teneurs et rapports entre acides hydroxycinnamiques libérés après hydrolyse alcaline étaient semblables chez les 3 hybrides, avec une libération faible d’acide para-coumarique caractéristique des génotypes bm3. La thioacydolyse confirme que la lignine des plantes bm3 est plus pauvre en unités syringyl, avec, de plus, la présence d’une unité 5-hydroxyguaiacyl. La lignine des plantes bm3 est un polymère plus condensé que la lignine des plantes normales. Observée à partir d’un seul hybride bm1, la diminution de la teneur en lignine a été semblable chez les plantes bm1 et bm3. Après thioacidolyse, la libération d’unités syringyl était équivalente entre bm1 et bm3. Mais la libération d’unité guaiacyl était beaucoup plus faible pour la lignine des plantes bm 1, avec des rapports syringyl/guaiacyl voisins de 0,3 pour les bm3 et de 1,3 pour les bm1. La lignine des plantes bm1 est également un polymère hautement condensé. Une variabilité importante pour la DOM et la DCF existe aussi entre hybrides normaux. Toutefois, les hybrides les plus digestibles présentent en général des défauts agronomiques importants, qu’il sera sans doute possible de corriger au niveau de lignées de second ou troisième cycle. Actuellement, on peut considérer que les voies normales et bm3 sont deux approches complémentaires de l’amélioration et de la compréhension de la digestibilité du maïs ensilage.

Oxidation of spruce milled-wood lignins in colloidal state catalyzed by horseradish peroxidase (HRP) and lignin peroxidase (LiP) in the presence of H 2 O 2 was compared in nonbuffered dimethyl-formamide/water. Lignins were characterized for their hydrodynamic properties by size-exclusion chromatography and structural bonding pattern by analysis after thioacidolysis. In contrast to LiP, HRP did not induce modification of lignin hydrodynamic properties. The lignin content in β-O-4-linked guaiacyl monomers and dimeric structures, however, decreased after oxidation by the two enzymes, indicating large structural changes in the polymer. Preferential degradation by both LiP and HRP of β-5 and β-1 lignin dimeric units was also observed. This suggests a greater susceptibility to enzyme oxidation, as compared to the 5-5′ and 4-O-5 lignin substructures. In conclusion, the action of HRP on the lignin polymer is similar in many respects to that of fungal LiP, but is distinctly different in its inability to cause a net destructuring of the macromolecular three-dimensional network.

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Cell wall-linked phenolics were investigated in maize internodes located at three positions of the stem (top-middle-bottom). While the lignin content did not change drastically with position, the amount of cell wall-ester linked p-coumaric acid sharply increased from the top to the bottom internodes of the stem. Conversely, the saponified ferulic acid content remained relatively unchanged along the stem. Moreover, the highest syringyl content of the β-O-4-lignin structures was found in the basal (most mature) internode. Therefore, enhanced p-coumaric esterification of the cell wall and preferential deposition of syringyl units in the lignin polymer might indicate an extended maturity stage of the cell wall of maize internodes. The bm3 mutation in the three maize hybrids is expressed by lignin reduction and ester-bound p-coumaric decrease in the mutant lines. Furthermore, all bm3 hybrids synthesised lignin polymers which were characterised by a very low S/G molar ratio (0.16-0.43). This ratio originates from the substantial reduction of the syringyl unit content in β-O-4-lignin structures compared with the normal lignin. The occurrence in the same range of the 5-hydroxyguaiacyl unit in bm3 lignin from each type of hybrids was noteworthy, demonstrating the high heritability of the bm3 mutation at the molecular level. The alkaline solubility of lignin was greater for the three mutant lines compared to the normal cultivars. Furthermore, the alkali-labile fraction of lignin of both normal and mutant lines had a monomeric composition which was consistent with the non-condensed structures of in-situ lignin.

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Cell wall might be considered as a composite material, made of fibre (cellulose), a matrix (lignin, hemicellulose) and fillers (water, simple organics, tannins). Its properties depend both on plant anatomy (heterogeneity and anisotropy of organs, tissues, cells and cell wall layers) and on the structure of the macromolecules, their orientational order, their associations and the resulting supramolecular structures as particularly discussed in the case of lignin networks. From selected examples, it is shown that natural or artificial lignocellulosic compounds such as woods, straws or reconstituted woods (fibre and particle boards) can be described as composite materials. Their most typical physico-chemico-mechanical properties are: shrinkage and water swelling behaviour, collapse in relation to extractive and tannin content, improvement of dimensional and biological stability by chemical modifications, anisotropic properties of orientated strand boards and fibre-reinforced polyester-based composites, and lastly, biological properties (digestibility, extensibility). As for synthetic composite materials, such an approach is a prerequisite for industrial production of competitive lignocellulosic products.

The hypothesis that auxin (IAA) and gibberellic acid (GA(3)) control the formation of lignin is confirmed for the primary phloem fibers and for the secondary xylem in the stem of Coleus blumel Benth. Indoleacetic acid alone, or a combination of high IAA/low GA(3) (w/w), induced short phloem fibers with thick secondary walls, that contained lignin rich in syringyl units (high ratio of syringyl/guaiacyl). On the other hand, a combination of high GA(3)/low IAA (w/w), which promoted the differentiation of long phloem fibers with thin walls, decreased the relative content of the syringyl units (low syringyl/guaiacyl ratio). In the secondary xylem, these hormonal treatments yielded only slight changes in the noncondensed monomeric guaiacyl units, confirming the relative stability of the guaiacyl lignification pattern in this tissue. In the xylem, indoleacetic acid alone, or a combination of high IAA/low GA(3) induced lignin poor in syringyl units (low syringyl/guaiacyl ratio). A combination of high GA(3)/low IAA promoted a relatively slight increase in syringyl yield, indicating greater responsiveness of the syringyl lignification pattern to growth regulators. The possible functional and technological significance of our results is discussed.

L'addition d'eau a une solution de lignine dans le DMF entraine la precipitation d'une partie de la lignine et le passage d'une autre fraction dans un etat colloidal. Toute la lignite presente peut etre transformee dans cet etat par des cycles successifs de solubilisation precpitation de la lignine non-colloidale. Cette lignine colloidale ne presente pas de difference significative de structure moleculaire ni de distribution de masse moleculaire par rapport a la lignine native, mais sa reactivite dans l'oxydation par la peroxydase de la lignine est beaucoup plus elevee

In the case of proanthocyanidins, reaction with vanillin in the presence of sulfuric acid is more sensitive than estimation by anthocyanidin formation. It is more specific than the assay by formaldehyde precipitation. Reaction with nitrous acid affords a selective estimation of hexahydroxydiphenoyl esters. These methods are applied to tannin estimation in wood extracts of 5 gymnosperms and 12 angiosperms and the values obtained compared to total phenols amounts

On a caracterise par analyses chimiques des fractions de lignine, les acides p-coumariques, feruliques et les polyosides associes, qui ont ete isoles de la paille d'un cultivar de riz «Balilla 28» et d'un de ses mutants a tige cassante. Des differences significatives ont ete observees entre les deux types de riz pour les teneurs en lignines (Klason, au bromure d'acetyle et insoluble dans les acides), en esters et ethers d'acides phenoliques, en polyosides hemicellulosiques et cellulosiques ainsi que pour les rendements d'extraction des fractions de lignine et d'hydrolyse par des polyosidases. Le caractere cassant des tiges du mutant ne peut donc pas etre simplement mis en relation avec les variations de composition chimique d'un constituant parietal particulier. Ces resultats sont discutes en fonction des variations correlatives de composition chimique des parois cellulaires et d'heterogeneite de composition monomerique des lignines

Structure des diastereoisomeres de type thioethylphenylpropane issus des thioacidolyses de lignine par chromatographie preparative combinee a la RMN et la spectroscopie de masse haute resolution

Four C -glucosylflavones were isolated from muskmelon leaves and shown to be 6-C-diglucosylapigenin (meloside A ),6- C -diglucosyl-luteolin (meloside L ) and the respective caffeyl esters of meloside A (meloside a ) and meloside L (meloside I ).

Extractive-free wheat straw, and the corresponding samples issued from its alkaline treatment — i.e. saponified wheat straw and alkali-soluble wheat lignin- were submitted to three chemical procedures of lignin characterization: nitrobenzene oxidation, acidolysis and thioacidolysis. The various performances of the three techniques were comparatively evaluated. The thioacidolysis procedure was found to have higher performances with regards to the two following criteria: the prominent alkyl aryl ether lignin structures were the almost exclusive source for the recovered degradation products; these products were obtained with a high yield. These advantages make the thioacidolysis procedure an unambiguous way to characterize grass lignins, even when present in low amounts.

Un protocole de dosage de la lignine insoluble dans l’acide sulfurique concentré, lignine Klason, est décrit : il comporte une étape de préhydrolyse par l’acide sulfurique 5 % et un lavage, en milieu chlorhydrique concentré, du résidu de préhydrolyse. Ce lavage permet d’améliorer la reproductibilité du dosage de la lignine après préhydrolyse et d’atteindre une reproductibilité comparable à celle obtenue par le dosage Klason standard. L’analyse élémentaire des préparations de lignines isolées au cours de ces dosages indique des variations complexes qui dépendent de la nature du produit analysé., A procedure for estimating lignin insoluble in concentrated acids, Klason lignin, is described ; it includes a 5 % sulfuric acid prehydrolysis step and washing in concentrated hydrochloric acid. This procedure allowed better reproducibility than without washing, of the same order as that given by the standard Klason procedure. Elemental analysis showed complex changes depending on the plant analysed.

Structure des diastereoisomeres syringyles issus de thioacidolyse de lignine de peuplier etablie apres HPLC preparative et analyses RMN du carbone 13 et du proton

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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.

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