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43-452: To qualify as a biodiversity hotspot on Myers' 2000 edition of the hotspot map, a region must meet two strict criteria: it must contain at least 1,500 species of vascular plants (more than 0.5% of the world's total) as endemics , and it has to have lost at least 70% of its primary vegetation. Globally, 36 zones qualify under this definition. These sites support nearly 60% of the world's plant, bird, mammal, reptile, and amphibian species , with

86-405: A smoke source to a wood fire. In cooking , lignin in the form of hardwood is an important source of these two compounds, which impart the characteristic aroma and taste to smoked foods such as barbecue . The main flavor compounds of smoked ham are guaiacol , and its 4-, 5-, and 6-methyl derivatives as well as 2,6-dimethylphenol. These compounds are produced by thermal breakdown of lignin in

129-423: A crucial part in conducting water and aqueous nutrients in plant stems. The polysaccharide components of plant cell walls are highly hydrophilic and thus permeable to water, whereas lignin is more hydrophobic . The crosslinking of polysaccharides by lignin is an obstacle for water absorption to the cell wall. Thus, lignin makes it possible for the plant's vascular tissue to conduct water efficiently. Lignin

172-507: A fibrous, tasteless material, insoluble in water and alcohol but soluble in weak alkaline solutions, and which can be precipitated from solution using acid. He named the substance "lignine", which is derived from the Latin word lignum , meaning wood. It is one of the most abundant organic polymers on Earth , exceeded only by cellulose and chitin . Lignin constitutes 30% of terrestrial non- fossil organic carbon on Earth, and 20 to 35% of

215-428: A high share of those species as endemics. Some of these hotspots support up to 15,000 endemic plant species, and some have lost up to 95% of their natural habitat. Biodiversity hotspots host their diverse ecosystems on just 2.4% of the planet's surface. Ten hotspots were originally identified by Myer; the current 36 used to cover more than 15.7% of all the land but have lost around 85% of their area. This loss of habitat

258-544: A lower redox potential than guaiacyl units. Because it is cross-linked with the other cell wall components, lignin minimizes the accessibility of cellulose and hemicellulose to microbial enzymes, leading to a reduced digestibility of biomass. Some ligninolytic enzymes include heme peroxidases such as lignin peroxidases , manganese peroxidases , versatile peroxidases , and dye-decolourizing peroxidases as well as copper-based laccases . Lignin peroxidases oxidize non-phenolic lignin, whereas manganese peroxidases only oxidize

301-444: A renewable source of aromatic compounds for the chemical industry, with an addressable market of more than $ 130bn. Given that it is the most prevalent biopolymer after cellulose , lignin has been investigated as a feedstock for biofuel production and can become a crucial plant extract in the development of a new class of biofuels. Lignin biosynthesis begins in the cytosol with the synthesis of glycosylated monolignols from

344-592: A small percentage of the total land area within biodiversity hotspots is now protected. Several international organizations are working to conserve biodiversity hotspots. Most biodiversity exists within the tropics; likewise, most hotspots are tropical. Of the 36 biodiversity hotspots, 15 are classified as old, climatically-buffered, infertile landscapes (OCBILs). These areas have been historically isolated from interactions with other climate zones, but recent human interaction and encroachment have put these historically safe hotspots at risk. OCBILs have mainly been threatened by

387-471: A substance under vacuum and at high temperature) with tetramethylammonium hydroxide (TMAH) or cupric oxide has also been used to characterize lignins. The ratio of syringyl lignol (S) to vanillyl lignol (V) and cinnamyl lignol (C) to vanillyl lignol (V) is variable based on plant type and can therefore be used to trace plant sources in aquatic systems (woody vs. non-woody and angiosperm vs. gymnosperm). Ratios of carboxylic acid (Ad) to aldehyde (Al) forms of

430-523: Is 63.4% carbon, 5.9% hydrogen, 0.7% ash (mineral components), and 30% oxygen (by difference), corresponding approximately to the formula (C 31 H 34 O 11 ) n . Lignin is a collection of highly heterogeneous polymers derived from a handful of precursor lignols. Heterogeneity arises from the diversity and degree of crosslinking between these lignols. The lignols that crosslink are of three main types, all derived from phenylpropane: coniferyl alcohol (3-methoxy-4-hydroxyphenylpropane; its radical, G,

473-497: Is a class of complex organic polymers that form key structural materials in the support tissues of most plants. Lignins are particularly important in the formation of cell walls , especially in wood and bark , because they lend rigidity and do not rot easily. Chemically, lignins are polymers made by cross-linking phenolic precursors. Lignin was first mentioned in 1813 by the Swiss botanist A. P. de Candolle , who described it as

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516-437: Is a radical-radical coupling, is catalysed by oxidative enzymes . Both peroxidase and laccase enzymes are present in the plant cell walls , and it is not known whether one or both of these groups participates in the polymerisation. Low molecular weight oxidants might also be involved. The oxidative enzyme catalyses the formation of monolignol radicals . These radicals are often said to undergo uncatalyzed coupling to form

559-405: Is achieved through a more environmentally viable process than generic plastic manufacturing. Lignin removed by the kraft process is usually burned for its fuel value, providing energy to power the paper mill. Two commercial processes exist to remove lignin from black liquor for higher value uses: LignoBoost (Sweden) and LignoForce (Canada). Higher quality lignin presents the potential to become

602-508: Is an antiquated remnant of the obsolete scala naturae , and the term is generally considered to be unscientific. Botanists define vascular plants by three primary characteristics: Cavalier-Smith (1998) treated the Tracheophyta as a phylum or botanical division encompassing two of these characteristics defined by the Latin phrase "facies diploida xylem et phloem instructa" (diploid phase with xylem and phloem). One possible mechanism for

645-471: Is colored, it yellows in air, and its presence weakens the paper. Once separated from the cellulose, it is burned as fuel. Only a fraction is used in a wide range of low volume applications where the form but not the quality is important. Mechanical, or high-yield pulp , which is used to make newsprint , still contains most of the lignin originally present in the wood. This lignin is responsible for newsprint's yellowing with age. High quality paper requires

688-463: Is derived from the coniferyl alcohol , which gives rise to G upon pyrolysis. In angiosperms some of the coniferyl alcohol is converted to S. Thus, lignin in angiosperms has both G and S components. Lignin's molecular masses exceed 10,000 u . It is hydrophobic as it is rich in aromatic subunits. The degree of polymerisation is difficult to measure, since the material is heterogeneous. Different types of lignin have been described depending on

731-416: Is digested by " Alteromonas-like sub-group " bacteria symbionts in the typhlosole sub-organ of its cecum . Pyrolysis of lignin during the combustion of wood or charcoal production yields a range of products, of which the most characteristic ones are methoxy -substituted phenols . Of those, the most important are guaiacol and syringol and their derivatives. Their presence can be used to trace

774-594: Is present in all vascular plants , but not in bryophytes , supporting the idea that the original function of lignin was restricted to water transport. It is covalently linked to hemicellulose and therefore cross-links different plant polysaccharides , conferring mechanical strength to the cell wall and by extension the plant as a whole. Its most commonly noted function is the support through strengthening of wood (mainly composed of xylem cells and lignified sclerenchyma fibres) in vascular plants. Finally, lignin also confers disease resistance by accumulating at

817-462: Is sometimes called guaiacyl), sinapyl alcohol (3,5-dimethoxy-4-hydroxyphenylpropane; its radical, S, is sometimes called syringyl), and paracoumaryl alcohol (4-hydroxyphenylpropane; its radical, H, is sometimes called 4-hydroxyphenyl). The relative amounts of the precursor "monomers" (lignols or monolignols) vary according to the plant source. Lignins are typically classified according to their syringyl/guaiacyl (S/G) ratio. Lignin from gymnosperms

860-884: Is supported by several molecular studies. Other researchers state that taking fossils into account leads to different conclusions, for example that the ferns (Pteridophyta) are not monophyletic. Hao and Xue presented an alternative phylogeny in 2013 for pre- euphyllophyte plants. † Horneophytaceae [REDACTED] † Cooksoniaceae † Aglaophyton † Rhyniopsida [REDACTED] † Catenalis † Aberlemnia † Hsuaceae † Renaliaceae [REDACTED] † Adoketophyton †? Barinophytopsida † Zosterophyllopsida † Hicklingia † Gumuia † Nothia Lycopodiopsida [REDACTED] † Zosterophyllum deciduum † Yunia † Eophyllophyton † Trimerophytopsida † Ibyka † Pauthecophyton † Cladoxylopsida Polypodiopsida [REDACTED] Lignin Lignin

903-535: Is why approximately 60% of the world's terrestrial life lives on only 2.4% of the land surface area. Caribbean Islands like Haiti and Jamaica are facing serious pressures on the populations of endemic plants and vertebrates as a result of rapid deforestation. Other areas include the Tropical Andes, Philippines, Mesoamerica, and Sundaland, which, under the current levels at which deforestation is occurring, will likely lose most of their plant and vertebrate species. Only

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946-416: The amino acid phenylalanine . These first reactions are shared with the phenylpropanoid pathway. The attached glucose renders them water-soluble and less toxic . Once transported through the cell membrane to the apoplast , the glucose is removed, and the polymerisation commences. Much about its anabolism is not understood even after more than a century of study. The polymerisation step, that

989-484: The wood used in the smokehouse. The conventional method for lignin quantitation in the pulp industry is the Klason lignin and acid-soluble lignin test, which is standardized procedures. The cellulose is digested thermally in the presence of acid. The residue is termed Klason lignin. Acid-soluble lignin (ASL) is quantified by the intensity of its Ultraviolet spectroscopy . The carbohydrate composition may be also analyzed from

1032-508: The "true" tracheophytes, the eutracheophytes. † Aglaophyton † Horneophytopsida † Rhyniophyta Lycopodiophyta † Zosterophyllophyta † Cladoxylopsida Equisetopsida (horsetails) Marattiopsida Psilotopsida (whisk ferns and adders'-tongues) Pteridopsida (true ferns) † Progymnospermophyta Cycadophyta (cycads) Ginkgophyta (ginkgo) Gnetophyta Pinophyta (conifers) Magnoliophyta (flowering plants) † Pteridospermatophyta (seed ferns) This phylogeny

1075-562: The H 2 O 2 required for the function of lignin peroxidase and other heme peroxidases . Bacteria lack most of the enzymes employed by fungi to degrade lignin, and lignin derivatives (aliphatic acids, furans, and solubilized phenolics) inhibit the growth of bacteria. Yet, bacterial degradation can be quite extensive, especially in aquatic systems such as lakes, rivers, and streams, where inputs of terrestrial material (e.g. leaf litter ) can enter waterways. The ligninolytic activity of bacteria has not been studied extensively even though it

1118-498: The Klason liquors, although there may be sugar breakdown products (furfural and 5-hydroxymethylfurfural ). A solution of hydrochloric acid and phloroglucinol is used for the detection of lignin (Wiesner test). A brilliant red color develops, owing to the presence of coniferaldehyde groups in the lignin. Thioglycolysis is an analytical technique for lignin quantitation . Lignin structure can also be studied by computational simulation. Thermochemolysis (chemical break down of

1161-399: The ability to grow independent roots, woody structure for support, and more branching. A proposed phylogeny of the vascular plants after Kenrick and Crane 1997 is as follows, with modification to the gymnosperms from Christenhusz et al. (2011a), Pteridophyta from Smith et al. and lycophytes and ferns by Christenhusz et al. (2011b) The cladogram distinguishes the rhyniophytes from

1204-853: The biodiversity hotspots approach has resulted in some criticism. Papers such as Kareiva & Marvier (2003) have pointed out that biodiversity hotspots (and many other priority region sets) do not address the concept of cost, and do not consider phylogenetic diversity . Vascular plant Vascular plants (from Latin vasculum  'duct'), also called tracheophytes ( UK : / ˈ t r æ k iː ə ˌ f aɪ t s / , US : / ˈ t r eɪ k iː ə ˌ f aɪ t s / ) or collectively tracheophyta ( / ˌ t r eɪ k iː ˈ ɒ f ɪ t ə / ; from Ancient Greek τραχεῖα ἀρτηρία ( trakheîa artēría )  'windpipe' and φυτά ( phutá )  'plants'), are plants that have lignified tissues (the xylem ) for conducting water and minerals throughout

1247-480: The dry mass of wood. Lignin is present in red algae , which suggest that the common ancestor of plants and red algae may have been pre-adapted to synthesize lignin. This finding also suggests that the original function of lignin may have been structural as it plays this role in the red alga Calliarthron , where it supports joints between calcified segments. The composition of lignin varies from species to species. An example of composition from an aspen sample

1290-413: The environment, lignin can be degraded either biotically via bacteria or abiotically via photochemical alteration, and oftentimes the latter assists in the former. In addition to the presence or absence of light, several of environmental factors affect the biodegradability of lignin, including bacterial community composition, mineral associations, and redox state. In shipworms , the lignin it ingests

1333-435: The lignin polymer . An alternative theory invokes an unspecified biological control. In contrast to other bio-polymers (e.g. proteins, DNA, and even cellulose), lignin resists degradation. It is immune to both acid- and base-catalyzed hydrolysis. The degradability varies with species and plant tissue type. For example, syringyl (S) lignin is more susceptible to degradation by fungal decay as it has fewer aryl-aryl bonds and

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1376-405: The lignin in lignocellulose , but others lack this ability. Most fungal lignin degradation involves secreted peroxidases . Many fungal laccases are also secreted, which facilitate degradation of phenolic lignin-derived compounds, although several intracellular fungal laccases have also been described. An important aspect of fungal lignin degradation is the activity of accessory enzymes to produce

1419-427: The lignols (Ad/Al) reveal diagenetic information, with higher ratios indicating a more highly degraded material. Increases in the (Ad/Al) value indicate an oxidative cleavage reaction has occurred on the alkyl lignin side chain which has been shown to be a step in the decay of wood by many white-rot and some soft rot fungi . Lignin and its models have been well examined by H and C NMR spectroscopy. Owing to

1462-444: The means of isolation. Many grasses have mostly G, while some palms have mainly S. All lignins contain small amounts of incomplete or modified monolignols, and other monomers are prominent in non-woody plants. Lignin fills the spaces in the cell wall between cellulose , hemicellulose , and pectin components, especially in vascular and support tissues: xylem tracheids , vessel elements and sclereid cells. Lignin plays

1505-586: The phenolic structures. Dye-decolorizing peroxidases, or DyPs, exhibit catalytic activity on a wide range of lignin model compounds, but their in vivo substrate is unknown. In general, laccases oxidize phenolic substrates but some fungal laccases have been shown to oxidize non-phenolic substrates in the presence of synthetic redox mediators. Well-studied ligninolytic enzymes are found in Phanerochaete chrysosporium and other white rot fungi . Some white rot fungi, such as Ceriporiopsis subvermispora , can degrade

1548-473: The plant. They also have a specialized non-lignified tissue (the phloem ) to conduct products of photosynthesis . The group includes most land plants ( c.  300,000 accepted known species) other than mosses . Vascular plants include the clubmosses , horsetails , ferns , gymnosperms (including conifers ), and angiosperms ( flowering plants ). They are contrasted with nonvascular plants such as mosses and green algae . Scientific names for

1591-421: The presumed evolution from emphasis on haploid generation to emphasis on diploid generation is the greater efficiency in spore dispersal with more complex diploid structures. Elaboration of the spore stalk enabled the production of more spores and the development of the ability to release them higher and to broadcast them further. Such developments may include more photosynthetic area for the spore-bearing structure,

1634-719: The relocation of indigenous groups and military actions, as the infertile ground has previously dissuaded human populations. The conservation of OCBILs within biodiversity hotspots has started to garner attention because current theories believe these sites provide not only high levels of biodiversity, but they have relatively stable lineages and the potential for high levels of speciation in the future. Because these sites are relatively stable, they can be classified as refugia . North and Central America The Caribbean South America Europe Africa Central Asia South Asia Southeast Asia and Asia-Pacific East Asia West Asia The high profile of

1677-434: The removal of lignin from the pulp. These delignification processes are core technologies of the papermaking industry as well as the source of significant environmental concerns. In sulfite pulping , lignin is removed from wood pulp as lignosulfonates , for which many applications have been proposed. They are used as dispersants , humectants , emulsion stabilizers , and sequestrants ( water treatment ). Lignosulfonate

1720-410: The site of pathogen infiltration, making the plant cell less accessible to cell wall degradation. Global commercial production of lignin is a consequence of papermaking. In 1988, more than 220 million tons of paper were produced worldwide. Much of this paper was delignified; lignin comprises about 1/3 of the mass of lignocellulose, the precursor to paper. Lignin is an impediment to papermaking as it

1763-463: The vascular plants group include Tracheophyta, Tracheobionta and Equisetopsida sensu lato . Some early land plants (the rhyniophytes ) had less developed vascular tissue; the term eutracheophyte has been used for all other vascular plants, including all living ones. Historically, vascular plants were known as " higher plants ", as it was believed that they were further evolved than other plants due to being more complex organisms. However, this

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1806-601: Was also the first family of water reducers or superplasticizers to be added in the 1930s as admixture to fresh concrete in order to decrease the water-to-cement ( w/c ) ratio, the main parameter controlling the concrete porosity , and thus its mechanical strength , its diffusivity and its hydraulic conductivity , all parameters essential for its durability. It has application in environmentally sustainable dust suppression agent for roads. Also, lignin can be used in making biodegradable plastic along with cellulose as an alternative to hydrocarbon-made plastics if lignin extraction

1849-417: Was first described in 1930. Many bacterial DyPs have been characterized. Bacteria do not express any of the plant-type peroxidases (lignin peroxidase, Mn peroxidase, or versatile peroxidases), but three of the four classes of DyP are only found in bacteria. In contrast to fungi, most bacterial enzymes involved in lignin degradation are intracellular, including two classes of DyP and most bacterial laccases. In

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