Flavonoids naringenin chalcone, naringenin, dihydrotricin, and tricin are lignin monomers in papyrus

Tritordeum, a hybrid cereal with a highly tricin-enriched lignin

The lignin from tritordeum straw, a hybrid cereal from crossbreeding of durum wheat and wild barley, was isolated and chemically characterized. Its composition and structure were studied by analytical pyrolysis (Py-GC/MS), nuclear magnetic resonance spectroscopy (NMR), Derivatization Followed by Reductive Cleavage (DFRC) method, and gel permeation chromatography (GPC). The data revealed an enrichment of guaiacyl (G) units (H:G:S of 3:61:36), which had a significant impact on the distribution of inter-unit linkages. The predominant linkages were the β-O-4' alkyl-aryl ethers (78 % of all linkages), with substantial proportions of condensed linkages such as phenylcoumarans (11 %), resinols (4 %), spirodienones (4 %), and dibenzodioxocins (2 %). Moreover, DFRC revealed that tridordeum straw lignin was partly acylated at the γ-OH with both acetates and p-coumarates. Acetates were principally attached to G-units, whereas p-coumarates were predominantly attached to S-units. Furthermore, and more importantly, tritordeum lignin incorporates remarkable amounts of a valuable flavone, tricin, exceeding 30 g per kilogram of straw. Given the diverse industrial applications associated with this high-value molecule, tritordeum straw emerges as a promising and sustainable resource for its extraction.

Hepatoprotective Effects of Flavonoids against Benzo[a]Pyrene-Induced Oxidative Liver Damage along Its Metabolic Pathways

Benzo[a]pyrene (B[a]P), a highly carcinogenic polycyclic aromatic hydrocarbon primarily formed during incomplete organic matter combustion, undergoes a series of hepatic metabolic reactions once absorbed into the body. B[a]P contributes to liver damage, ranging from molecular DNA damage to the onset and progression of various diseases, including cancer. Specifically, B[a]P induces oxidative stress via reactive oxygen species generation within cells. Consequently, more research has focused on exploring the underlying mechanisms of B[a]P-induced oxidative stress and potential strategies to counter its hepatic toxicity. Flavonoids, natural compounds abundant in plants and renowned for their antioxidant properties, possess the ability to neutralize the adverse effects of free radicals effectively. Although extensive research has investigated the antioxidant effects of flavonoids, limited research has delved into their potential in regulating B[a]P metabolism to alleviate oxidative stress. This review aims to consolidate current knowledge on B[a]P-induced liver oxidative stress and examines the role of flavonoids in mitigating its toxicity.

Advances and prospects of natural dietary polyphenols as G-quadruplex stabilizers in biomedical applications

G-quadruplexes (G4s) have arrested continuous interest in cancer research, and targeting G4s with small molecules has become an ideal approach for drug development. Plant-based dietary polyphenols have attracted much attention for their remarkable anti-cancer effects. Studies have suggested that polyphenols exhibit interesting scaffolds to bind G4s, which can effectively downregulate the proto-oncogenes by stabilizing those G4 structures. Therefore, this review not only summarizes studies on natural dietary polyphenols (including analogs) as G4 stabilizers, but also reveals their anti-cancer activities. Furthermore, the structural and antioxidant insights of polyphenols with G4s are discussed, and future development is proposed. These insights may pave the way for the development of the next generation of anti-cancer drugs targeting nucleic acids.

Selecting Suitable Near-Native Lignins for Research

There are several methods to isolate near-native lignins, including milled-wood lignin, enzymatic lignin, cellulolytic enzyme lignin, and enzymatic mild-acidolysis lignin. Which one is the most representative of the native lignin? Herein, near-native lignins were isolated from different plant groups and structurally analyzed to determine how well these lignins represented their native lignin counterparts. Analytical methods were applied to understand the molecular weight, monomer composition, and distribution of interunit linkages in the structure of the lignins. The results indicated that either enzymatic lignin or cellulolytic enzyme lignin may be used to represent native lignin in softwoods and hardwoods. None of the lignins, however, appeared to represent native lignins in grasses (monocot plants) because of substantial syringyl/guaiacyl differences. Complicating the understanding of grass lignin structure, large amounts of hydroxycinnamates acylate their polysaccharides and, when released, are often conflated with actual lignin monomers.

Quantitative proteomics and metabolomics analysis reveals the response mechanism of alfalfa (Medicago sativa L.) to o-coumaric acid stress

O-coumaric acid (OCA), as a significant phenolic allelochemical found in hairy vetch (Vicia villosa Roth.), that can hinder the growth of alfalfa (Medicago sativa L.), particularly the growth of alfalfa roots. Nonetheless, the mechanism by which OCA inhibits alfalfa root growth remains unclear. In this study, a liquid chromatography tandem mass spectrometry (LC-MS/MS)-based quantitative proteomics analysis was carried out to identify differentially accumulated proteins (DAPs) under OCA treatment. The findings indicated that 680 proteins were DAPs in comparison to the control group. Of those, 333 proteins were up-regulated while 347 proteins were down-regulated. The enrichment analysis unveiled the significance of these DAPs in multiple biological and molecular processes, particularly in ribosome, phenylpropanoid biosynthesis, glutathione metabolism, glycolysis/gluconeogenesis and flavonoid biosynthesis. The majority of DAPs reside in the cytoplasm (36.62%), nucleus (20.59%) and extracellular space (14.12%). In addition, phenylalanine deaminase was identified as a potential chemical-induced regulation target associated with plant lignin formation. DAPs were mainly enriched in flavonoid biosynthesis pathways, which were related to plant root size. Using the UPLC-ESI-MS/MS technique and database, a total of 87 flavonoid metabolites were discovered. The metabolites were predominantly enriched for biosynthesizing naringenin chalcone, which was linked to plant lignin formation, aligning with the enrichment outcomes of DAPs. Consequently, it was deduced that OCA impacted the structure of cell walls by mediating the synthesis of lignin in alfalfa roots, subsequently inducing wilt. Furthermore, a range of proteins have been identified as potential candidates for the breeding of alfalfa strains with enhanced stress tolerance.

Integrated metabolome, full-length sequencing, and transcriptome analyses unveil the molecular mechanisms of color formation of the canary yellow and red bracts of Bougainvillea × buttiana 'Chitra'

Bougainvillea is a typical tropical flower of great ornamental value due to its colorful bracts. The molecular mechanism behind color formation is not well-understood. Therefore, this research conducted metabolome analysis, transcriptome analysis, and multi-flux full-length sequencing in two color bracts of Bougainvillea × buttiana 'Chitra' to investigate the significantly different metabolites (SDMs) and differentially expressed genes (DEGs). Overall, 261 SDMs, including 62 flavonoids and 26 alkaloids, were detected, and flavonols and betalains were significantly differentially accumulated among the two bracts. Furthermore, the complete-length transcriptome of Bougainvillea × buttiana was also developed, which contained 512 493 non-redundant isoforms. Among them, 341 210 (66.58%) displayed multiple annotations in the KOG, GO, NR, KEGG, Pfam, Swissprot, and NT databases. RNA-seq findings revealed that 3610 DEGs were identified between two bracts. Co-expression analysis demonstrated that the DEGs and SDMs involved in flavonol metabolism (such as CHS, CHI, F3H, FLS, CYP75B1, kaempferol, and quercetin) and betacyanin metabolism (DODA, betanidin, and betacyanins) were the main contributors for the canary yellow and red bract formation, respectively. Further investigation revealed that several putative transcription factors (TFs) might interact with the promoters of the genes mentioned above. The expression profiles of the putative TFs displayed that they may positively and negatively regulate the structural genes' expression profiles. The data revealed a potential regulatory network between important genes, putative TFs, and metabolites in the flavonol and betacyanin biosynthesis of Bougainvillea × buttiana 'Chitra' bracts. These findings will serve as a rich genetic resource for future studies that could create new color bracts.

Menadione Contribution to the In Vitro Radical Scavenging Potential of Phytochemicals Naringenin and Lignin

Vitamin K3 (menadione), classified as a pro-vitamin, is a synthetic form of the fat-soluble family of vitamin K compounds. The combination of the vitamin with other molecules sharing structural and/or functional similarities, such as naturally occurring polyphenols, vitamins, or biopolymers, could potentiate mutual improvement of their antioxidant activity. The aim of the present study was to evaluate the role and contribution of vitamin K3 to the in vitro radical scavenging capacity of double and triple combinations with the phytochemicals naringenin and lignin, as well as assess possible intermolecular interactions between the bioactive compounds. Comparative analyses of the DPPH and ABTS radical scavenging activity of the pure substances vitamin K3, naringenin, and lignin; the two-component systems lignin/vitamin K3 and vitamin K3/naringenin; and the triple combination vitamin K3/flavonoid/lignin were carried out. The experimental results demonstrated increased DPPH and ABTS activities of the vitamin in combination with lignin compared to those of the two pure substances, i.e., a synergistic effect was observed. The registered significant increases in the radical scavenging activity of the triple combination determined via both methods are indicative of a remarkable potentiation effect, i.e., higher antioxidant potential exceeding the additive activity of the three pure substances.

Application of 2D NMR Spectroscopy in Combination with Chemometric Tools for Classification of Natural Lignins

Lignin is considered a promising renewable source of valuable chemical compounds and a feedstock for the production of various materials. Its suitability for certain directions of processing is determined by the chemical structure of its macromolecules. Its formation depends on botanical origin, isolation procedure and other factors. Due to the complexity of the chemical composition, revealing the structural differences between lignins of various origins is a challenging task and requires the use of the most informative methods for obtaining and processing data. In the present study, a combination of two-dimensional nuclear magnetic resonance (2D NMR) spectroscopy and multivariate analysis of heteronuclear single quantum coherence (HSQC) spectra is proposed. Principal component analysis and hierarchical cluster analysis techniques demonstrated the possibility to effectively classify lignins at the level of belonging to classes and families of plants, and in some cases individual species, with an error rate for data classification of 2.3%. The reverse transformation of loading plots into the corresponding HSQC loading spectra allowed for structural information to be obtained about the latent components of lignins and their structural fragments (biomarkers) responsible for certain differences. As a result of the analysis of 34 coniferous, deciduous, and herbaceous lignins, 10 groups of key substructures were established. In addition to syringyl, guaiacyl, and p-hydroxyphenyl monomeric units, they include various terminal substructures: dihydroconiferyl alcohol, balanopholin, cinnamic acids, and tricin. It was shown that, in some cases, the substructures formed during the partial destruction of biopolymer macromolecules also have a significant effect on the classification of lignins of various origins.

Lignin, the Lignification Process, and Advanced, Lignin-Based Materials

At a time when environmental considerations are increasingly pushing for the application of circular economy concepts in materials science, lignin stands out as an under-used but promising and environmentally benign building block. This review focuses (A) on understanding what we mean with lignin, i.e., where it can be found and how it is produced in plants, devoting particular attention to the identity of lignols (including ferulates that are instrumental for integrating lignin with cell wall polysaccharides) and to the details of their coupling reactions and (B) on providing an overview how lignin can actually be employed as a component of materials in healthcare and energy applications, finally paying specific attention to the use of lignin in the development of organic shape-memory materials.

Variations in the composition and structure of the lignins of oat (Avena sativa L.) straws according to variety and planting season

The differences in the composition and structure of the lignins from straws of different oat (Avena sativa L.) varieties, planted in two seasons (winter and spring), were studied in detail by different analytical techniques such as pyrolysis coupled to gas chromatography-mass spectrometry (Py-GC/MS), two-dimensional nuclear magnetic resonance (2D-NMR), derivatization followed by reductive cleavage (DFRC), and gel permeation chromatography (GPC). Overall, the analyses revealed that oat straw lignins were enriched in guaiacyl (G; 50-56 %) and syringyl (S; 39-44 %) units, with relatively lower amounts of p-hydroxyphenyl (H; 4-6 %) units. The lignins also incorporated significant quantities of p-coumarates (9-14 % of total lignin units), which are acylating the γ-OH of the lignin side chains, and predominantly over the S units. Furthermore, oat straw lignins also incorporated considerable amounts of the flavone tricin (5-12 % of total lignin units). Interestingly, this study revealed that the lignin content and composition of the oat straws varies with genotype and planting season. Since p-coumarates and tricin are high-value aromatic compounds especially attractive from a biorefinery point of view, the information disclosed here is highly relevant to plant breeding programs aimed at developing functional foods and lignin modifications for improved biorefinery applications.

α-Glucosidase inhibitory activities of flavonoid derivatives isolated from Bouea macrophylla: in vitro and in silico studies

In continuation of our search for bioactive compounds from the Bouea macrophylla (B. macrophylla) plant, we describe herein eight flavonoid-type compounds including mearsetin (1), mearnsitrin (2), kampferol (3), afzelin (4), quercetin (5), quercitrin (6), myricitin (7), and naringenin (8) with the aim of investigating their antidiabetic properties. Compounds 3 and 5 were selected for aromatic bromination to provide two new products 3a and 5a, respectively. All compounds showed promising α-glucosidase inhibition, with IC₅₀ values ranging from 9.2 to 266 μM apart from compound (2). Remarkably, compound 5a, 8-bromoquercetin, showed the highest inhibition activity, and it was thirty-seven times better than the standard drug acarbose. Pose 261/compound 5a interacted well with enzyme 3TOPin silico docking, and the complex of pose 261 and target enzyme proved its stability in MD. Compound 5a, pose 261 was predicted to be safe and seemed to have good absorption, distribution, metabolism, and excretion properties as assessed via the ADMET model in silico. Our findings revealed the α-glucosidase inhibitory potential of the flavonoids isolated from the leaves of B. macrophylla with a predictive pharmacokinetics profile, which may be helpful in their development as potential drugs.

Different combinations of laccase paralogs nonredundantly control the amount and composition of lignin in specific cell types and cell wall layers in Arabidopsis

Vascular plants reinforce the cell walls of the different xylem cell types with lignin phenolic polymers. Distinct lignin chemistries differ between each cell wall layer and each cell type to support their specific functions. Yet the mechanisms controlling the tight spatial localization of specific lignin chemistries remain unclear. Current hypotheses focus on control by monomer biosynthesis and/or export, while cell wall polymerization is viewed as random and nonlimiting. Here, we show that combinations of multiple individual laccases (LACs) are nonredundantly and specifically required to set the lignin chemistry in different cell types and their distinct cell wall layers. We dissected the roles of Arabidopsis thaliana LAC4, 5, 10, 12, and 17 by generating quadruple and quintuple loss-of-function mutants. Loss of these LACs in different combinations led to specific changes in lignin chemistry affecting both residue ring structures and/or aliphatic tails in specific cell types and cell wall layers. Moreover, we showed that LAC-mediated lignification has distinct functions in specific cell types, waterproofing fibers, and strengthening vessels. Altogether, we propose that the spatial control of lignin chemistry depends on different combinations of LACs with nonredundant activities immobilized in specific cell types and cell wall layers.

Different combinations of laccase paralogs nonredundantly control the amount and composition of lignin in specific cell types and cell wall layers in Arabidopsis

Vascular plants reinforce the cell walls of the different xylem cell types with lignin phenolic polymers. Distinct lignin chemistries differ between each cell wall layer and each cell type to support their specific functions. Yet the mechanisms controlling the tight spatial localization of specific lignin chemistries remain unclear. Current hypotheses focus on control by monomer biosynthesis and/or export, while cell wall polymerization is viewed as random and nonlimiting. Here, we show that combinations of multiple individual laccases (LACs) are nonredundantly and specifically required to set the lignin chemistry in different cell types and their distinct cell wall layers. We dissected the roles of Arabidopsis thaliana LAC4, 5, 10, 12, and 17 by generating quadruple and quintuple loss-of-function mutants. Loss of these LACs in different combinations led to specific changes in lignin chemistry affecting both residue ring structures and/or aliphatic tails in specific cell types and cell wall layers. Moreover, we showed that LAC-mediated lignification has distinct functions in specific cell types, waterproofing fibers, and strengthening vessels. Altogether, we propose that the spatial control of lignin chemistry depends on different combinations of LACs with nonredundant activities immobilized in specific cell types and cell wall layers.

Chemical composition of the lipophilic compounds from the rind and pith of papyrus (Cyperus papyrus L.) stems

Papyrus (Cyperus papyrus L.) is a sedge plant with a high rate of biomass productivity that represents an interesting raw material to produce chemicals, materials and fuels, which are currently still obtained from fossil resources, in the context of a lignocellulosic biorefinery. In this work, the content and chemical composition of the lipids present in papyrus stems were thoroughly studied. For this, the papyrus stems were separated into the rind and the pith. The lipid content accounted for 4.1% in the rind and 4.9% in the pith (based on dry matter). The main compounds identified in both parts of the papyrus stem were hydrocarbons, n-fatty acids, 2-hydroxyfatty acids, alcohols, alkylamides, mono- and diglycerides, steroids (sterols, ketones, hydrocarbons, esters and glycosides), tocopherols, tocopherol esters, phytol, phytol esters, alkyl ferulates, ω-carboxyalkyl ferulates (and their monoglycerides), and acylglycerol glycosides. The rind presented a predominance of n-fatty acids (6790 mg/kg; that represented 28.6% of all identified compounds), steroid compounds (6255 mg/kg; 26.3%), phytol and phytol esters (4985 mg/kg; 21.0%), and isoprenoid hydrocarbons, namely phytadiene and squalene (2660 mg/kg; 11.2%), while the most abundant lipids in the pith were steroids (8600 mg/kg; 44.4% of all identified compounds) and fatty acids (6245 mg/kg; 32.2%). Due to the great diversity and significant abundance of the compounds identified in papyrus, it can be considered as a potential raw material for biorefineries to obtain valuable phytochemicals of interest to various industrial sectors.

Plant biomechanics and resilience to environmental changes are controlled by specific lignin chemistries in each vascular cell type and morphotype

The biopolymer lignin is deposited in the cell walls of vascular cells and is essential for long-distance water conduction and structural support in plants. Different vascular cell types contain distinct and conserved lignin chemistries, each with specific aromatic and aliphatic substitutions. Yet, the biological role of this conserved and specific lignin chemistry in each cell type remains unclear. Here, we investigated the roles of this lignin biochemical specificity for cellular functions by producing single cell analyses for three cell morphotypes of tracheary elements, which all allow sap conduction but differ in their morphology. We determined that specific lignin chemistries accumulate in each cell type. Moreover, lignin accumulated dynamically, increasing in quantity and changing in composition, to alter the cell wall biomechanics during cell maturation. For similar aromatic substitutions, residues with alcohol aliphatic functions increased stiffness whereas aldehydes increased flexibility of the cell wall. Modifying this lignin biochemical specificity and the sequence of its formation impaired the cell wall biomechanics of each morphotype and consequently hindered sap conduction and drought recovery. Together, our results demonstrate that each sap-conducting vascular cell type distinctly controls their lignin biochemistry to adjust their biomechanics and hydraulic properties to face developmental and environmental constraints.

Deficiency in flavonoid biosynthesis genes CHS, CHI, and CHIL alters rice flavonoid and lignin profiles

Lignin is a complex phenylpropanoid polymer deposited in the secondary cell walls of vascular plants. Unlike most gymnosperm and eudicot lignins that are generated via the polymerization of monolignols, grass lignins additionally incorporate the flavonoid tricin as a natural lignin monomer. The biosynthesis and functions of tricin-integrated lignin (tricin-lignin) in grass cell walls and its effects on the utility of grass biomass remain largely unknown. We herein report a comparative analysis of rice (Oryza sativa) mutants deficient in the early flavonoid biosynthetic genes encoding CHALCONE SYNTHASE (CHS), CHALCONE ISOMERASE (CHI), and CHI-LIKE (CHIL), with an emphasis on the analyses of disrupted tricin-lignin formation and the concurrent changes in lignin profiles and cell wall digestibility. All examined CHS-, CHI-, and CHIL-deficient rice mutants were largely depleted of extractable flavones, including tricin, and nearly devoid of tricin-lignin in the cell walls, supporting the crucial roles of CHS and CHI as committed enzymes and CHIL as a noncatalytic enhancer in the conserved biosynthetic pathway leading to flavone and tricin-lignin formation. In-depth cell wall structural analyses further indicated that lignin content and composition, including the monolignol-derived units, were differentially altered in the mutants. However, regardless of the extent of the lignin alterations, cell wall saccharification efficiencies of all tested rice mutants were similar to that of the wild-type controls. Together with earlier studies on other tricin-depleted grass mutant and transgenic plants, our results reflect the complexity in the metabolic consequences of tricin pathway perturbations and the relationships between lignin profiles and cell wall properties.

The Sorghum (Sorghum bicolor) Brown Midrib 30 Gene Encodes a Chalcone Isomerase Required for Cell Wall Lignification

In sorghum (Sorghum bicolor) and other C4 grasses, brown midrib (bmr) mutants have long been associated with plants impaired in their ability to synthesize lignin. The brown midrib 30 (Bmr30) gene, identified using a bulk segregant analysis and next-generation sequencing, was determined to encode a chalcone isomerase (CHI). Two independent mutations within this gene confirmed that loss of its function was responsible for the brown leaf midrib phenotype and reduced lignin concentration. Loss of the Bmr30 gene function, as shown by histochemical staining of leaf midrib and stalk sections, resulted in altered cell wall composition. In the bmr30 mutants, CHI activity was drastically reduced, and the accumulation of total flavonoids and total anthocyanins was impaired, which is consistent with its function in flavonoid biosynthesis. The level of the flavone lignin monomer tricin was reduced 20-fold in the stem relative to wild type, and to undetectable levels in the leaf tissue of the mutants. The bmr30 mutant, therefore, harbors a mutation in a phenylpropanoid biosynthetic gene that is key to the interconnection between flavonoids and monolignols, both of which are utilized for lignin synthesis in the grasses.