Lichen product

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Lobaria pulmonaria, a lichen that contains lichen products such as stictic acid and gyrophoric acid. Lungwort (4504575158).jpg
Lobaria pulmonaria , a lichen that contains lichen products such as stictic acid and gyrophoric acid.

Lichen products, also known as lichen substances, are organic compounds produced by a lichen. Specifically, they are secondary metabolites. Lichen products are represented in several different chemical classes, including terpenoids, orcinol derivatives, chromones, xanthones, depsides, and depsidones. Over 1000 lichen products of known chemical structure have been reported in the scientific literature, and most of these compounds are exclusively found in lichens. [1] Examples of lichen products include usnic acid (a dibenzofuran), atranorin (a depside), lichexanthone (a xanthone), salazinic acid (a depsidone), and isolichenan, an α-glucan. Many lichen products have biological activity, and research into these effects is ongoing. [2]

Contents

Biosynthesis

Most lichen products are biochemically synthesized via the acetyl-polymalonyl pathway (also known as polyketide pathway), while only a few originate from the mevalonate and shikimate biosynthetic pathways. [3]

Occurrence

Lichen products accumulate on the outer walls of the fungal hyphae, and are quite stable. Crystal deposits can be visualised using scanning electron microscopy. [4] For this reason, even very old herbarium specimens can be analysed. [5] The amount of lichen products in lichen (as a percentage of dry weight) is typically between 0.1%–10%, although in some instances it may be as high as 30%. [6] They are usually found in the medulla, or less commonly, the cortex. [7]

In 1907, Wilhelm Zopf identified and classified about 150 lichen products. Seventy years later, this number had risen to 300, and by 1995, 850 lichen products were known; [8] as of 2021, more than 1000 have been identified. [9] Analytical methods were developed in the 1970s using thin-layer chromatography for the routine identification of lichen products. [10] [11] More recently, published techniques demonstrate ways to more efficiently harvest secondary metabolites from lichen samples. [12]

Chemical isolateLichen sourceResearched activity and uses
Atranorin Cetraria islandica Analgesic, anti-inflammatory, antimicrobial [13] [14]
Constipatic acid Xanthoparmelia
Lichexanthone Hypotrachyna osseoalba
Portentol Roccella portentosaAnticancer [15]
Salazinic acid Parmotrema, Bulbothrix Antibacterial [16] [17]
Usnic acid Usnea Antibacterial, [18] adrenergic activity [19]

Detection and analysis

Many lichen products can be screened with simple chemical tests long used in lichen identification. In spot tests, a small amount of reagent is applied directly to the thallus (or to a particular layer, such as the outer cortex or inner medulla) and any colour change is recorded. Because different compounds tend to give consistent reactions, these tests can help separate morphologically similar taxa or chemotypes, and the results are often recorded for herbarium specimens as part of routine work. Spot tests are only a first pass, though: colour intensity can be hard to standardize, and a given reaction does not always point to a single compound. For a more informative profile, many workers still use thin-layer chromatography, which separates metabolites from a solvent extract on a coated plate and produces a characteristic pattern of spots that can be compared with standardized protocols. [20]

Laboratory identification usually combines chromatography with spectroscopic methods. High-performance liquid chromatography (HPLC) is widely used to separate and help identify lichen substances, particularly those that are too non-volatile or heat-sensitive for gas chromatography; gradient methods can improve separation in complex extracts. Modern workflows increasingly use "hyphenated" approaches, coupling chromatographic separation with detectors such as UV–visible or infrared spectroscopy, mass spectrometry, and NMR spectroscopy. This can speed up dereplication (recognizing common, previously described compounds early) and focus effort on unusual or bioactive products. Complementing extract-based work, in situ techniques apply spectroscopy or mass spectrometry directly to intact thalli or thin sections, reducing artefacts from extraction and allowing researchers to map where metabolites accumulate within the lichen, including cases where concentrations differ between vegetative tissues and reproductive structures. [20]

Use in taxonomy

Lichen products play a crucial role in differentiating lichenised fungi, particularly in groups where morphological characteristics are less distinct. This approach is notably applied in the genus Lepraria , which lacks sexual reproduction and ascomata (fruiting bodies), typically key features for species identification. [21] Similarly, in genera with more complex structures like the crustose genus Ochrolechia , [22] and the fruticose Cladonia , [23] [24] the presence, absence, or substitution of specific lichen products is frequently used to distinguish species, especially when these variations align with differences in geographical distribution. [25]

References

  1. ↑ Ranković & Kosanić 2019, p. 1.
  2. ↑ Molnár, Katalin; Farkas, Edit (2010). "Current Results on Biological Activities of Lichen Secondary Metabolites: a Review". Zeitschrift für Naturforschung C. 65 (3–4): 157–173. doi: 10.1515/znc-2010-3-401 . PMID   20469633.
  3. ↑ Stocker-Wörgötter, Elfie; Cordeiro, Lucimara Mach Cortes; Iacomini, Marcello (2013). "Accumulation of Potential Pharmaceutically Relevant Lichen Metabolites in Lichens and Cultured Lichen Symbionts". Studies in Natural Products Chemistry. Vol. 39. Elsevier. pp. 337–380. doi:10.1016/b978-0-444-62615-8.00010-2. ISBN   978-0-444-62615-8.
  4. ↑ Stocker-Wörgötter, Elfie (2008). "Metabolic diversity of lichen-forming ascomycetous fungi: culturing, polyketide and shikimatemetabolite production, and PKS genes". Natural Product Reports. 25 (1): 188–200. doi:10.1039/b606983p. PMID   18250902.
  5. ↑ Culberson, Chicita F.; Elix, john A. (1989). "Lichen Substances". Methods in Plant Biochemistry. Vol. 1. pp. 509–535. doi:10.1016/b978-0-12-461011-8.50021-4. ISBN   9780124610118.
  6. ↑ Ranković & Kosanić 2019, p. 4.
  7. ↑ Ranković & Kosanić 2019, p. 5.
  8. ↑ Culberson, Chicita F.; Culberson, William Louis (2001). "Future directions in lichen chemistry". The Bryologist. 104 (2): 230–234. doi:10.1639/0007-2745(2001)104[0230:FDILC]2.0.CO;2. JSTOR   3244888.
  9. ↑ Kalra, Rishu; Conlan, Xavier A.; Goel, Mayurika (2021). "Lichen allelopathy: a new hope for limiting chemical herbicide and pesticide use". Biocontrol Science and Technology. 31 (8): 773–796. doi:10.1080/09583157.2021.1901071.
  10. ↑ Culberson, Chicita F.; Kristinsson, Hör-Dur (1970). "A standardized method for the identification of lichen products". Journal of Chromatography A. 46: 85–93. doi:10.1016/s0021-9673(00)83967-9.
  11. ↑ Culberson, Chicita F. (1972). "Improved conditions and new data for identification of lichen products by standardized thin-layer chromatographic method". Journal of Chromatography A. 72 (1): 113–125. doi:10.1016/0021-9673(72)80013-x. PMID   5072880.
  12. ↑ Komaty, Sarah; Letertre, Marine; Dang, Huyen Duong; Jungnickel, Harald; Laux, Peter; Luch, Andreas; Carrié, Daniel; Merdrignac-Conanec, Odile; Bazureau, Jean-Pierre; Gauffre, Fabienne; Tomasi, Sophie; Paquin, Ludovic (2016). "Sample preparation for an optimized extraction of localized metabolites in lichens: Application to Pseudevernia furfuracea" (PDF). Talanta. 150: 525–530. doi:10.1016/j.talanta.2015.12.081. PMID   26838439.
  13. ↑ Studzinska-Sroka, Elzbieta; Galanty, Agnieszka; Bylka, Wieslawa (7 November 2017). "Atranorin - An Interesting Lichen Secondary Metabolite". Mini-Reviews in Medicinal Chemistry. 17 (17): 1633–1645. doi:10.2174/1389557517666170425105727. PMID   28443519.
  14. ↑ Jaeck, Andreas. "Atranorin". www.internetchemie.info.
  15. ↑ Cheng, Bichu; Trauner, Dirk (2015-11-04). "A Highly Convergent and Biomimetic Total Synthesis of Portentol" . Journal of the American Chemical Society. 137 (43): 13800–13803. doi:10.1021/jacs.5b10009. ISSN   0002-7863. PMID   26471956.
  16. ↑ Candan, Mehmet; Yılmaz, Meral; Tay, Turgay; Erdem, Murat; Türk, Ayşen Özdemir (2007-08-01). "Antimicrobial Activity of Extracts of the Lichen Parmelia sulcata and its Salazinic Acid Constituent". Zeitschrift für Naturforschung C. 62 (7–8): 619–621. doi: 10.1515/znc-2007-7-827 . ISSN   1865-7125. PMID   17913083.
  17. ↑ Manojlović, Nedeljko; Ranković, Branislav; Kosanić, Marijana; Vasiljević, Perica; Stanojković, Tatjana (October 2012). "Chemical composition of three Parmelia lichens and antioxidant, antimicrobial and cytotoxic activities of some their major metabolites" . Phytomedicine. 19 (13): 1166–1172. doi:10.1016/j.phymed.2012.07.012. PMID   22921748.
  18. ↑ "Wikispaces".
  19. ↑ Harris N. J. (1961), Honors Thesis, Clark University, Worcester, Massachusetts
  20. 1 2 Le Pogam, Pierre; Herbette, Gaëtan; Boustie, Joël (2015). "Analysis of lichen metabolites, a variety of approaches". Recent Advances in Lichenology. New Delhi: Springer India. p. 229–261. doi:10.1007/978-81-322-2181-4_11. ISBN   978-81-322-2180-7.
  21. ↑ Lendemer, James C. (2011). "A taxonomic revision of the North American species of Lepraria s.l. that produce divaricatic acid, with notes on the type species of the genus L. incana". Mycologia. 103 (6): 1216–1229. doi:10.3852/11-032. PMID   21642343.
  22. ↑ Kukwa, Martin (2011). The lichen genus 'Ochrolechia' in Europe. Gdańsk; Sopot: Fundacja Rozwoju Uniwersytetu Gdańskiego. ISBN   978-83-7531-170-9.
  23. ↑ Stenroos, Soili (1989). "Taxonomy of the Cladonia coccifera group. 1". Annales Botanici Fennici. 26: 157–168.
  24. ↑ Timsina, Brinda A.; Hausner, Georg; Piercey-Normore, Michele D. (2014). "Evolution of ketosynthase domains of polyketide synthase genes in the Cladonia chlorophaea species complex (Cladoniaceae)". Fungal Biology. 118 (11): 896–909. doi:10.1016/j.funbio.2014.08.001. PMID   25442293.
  25. ↑ Lumbsch, H. Thorsten; Leavitt, Steven D. (2011). "Goodbye morphology? A paradigm shift in the delimitation of species in lichenized fungi". Fungal Diversity. 50 (1): 59–72. doi:10.1007/s13225-011-0123-z.

Cited literature

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