# Biofluorescence
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{{Short description|Light emission in lifeforms with external source}}
{{distinguish|Bioluminescence}}
[[File:Neon-green fluorescence in the desert gecko Pachydactylus rangei caused by iridophores - video 1 -41598 2020 79706 MOESM2 ESM.webm|thumb|A ''[Pachydactylus rangei](/source/Pachydactylus_rangei)'' exhibiting biofluorescence under ultraviolet light]]
'''Biofluorescence''' is [fluorescence](/source/fluorescence) exhibited by a living organism: part of the organism absorbs [light](/source/light) or other [radiation](/source/electromagnetic_radiation) at one [wavelength](/source/wavelength) and emits [visible light](/source/visible_spectrum) at another, usually longer. The absorbed radiation is often blue or [ultraviolet](/source/ultraviolet), while the light emitted is typically green, red, or anything in between. Biofluorescence requires an external light source and a fluorescent biomolecular substance, which is often one or more [protein](/source/protein)s, but can consist of other [biomolecule](/source/biomolecule)s.
A perceptible example of fluorescence occurs when the absorbed radiation is ultraviolet, thus invisible to the human eye, while the emitted light is in the visible spectrum; this gives the fluorescent substance a distinct [color](/source/color) that can only be seen when it is exposed to UV light.
Since biofluorescence was discovered in ''[Aequorea victoria](/source/Aequorea_victoria)'' and the [green fluorescent protein](/source/green_fluorescent_protein) structure was resolved, many other organisms have been shown to exhibit biofluorescence and many new fluorescent proteins have been discovered.[{{Cite journal |last1=Labas |first1=Y. A. |last2=Gurskaya |first2=N. G. |last3=Yanushevich |first3=Y. G. |last4=Fradkov |first4=A. F. |last5=Lukyanov |first5=K. A. |last6=Lukyanov |first6=S. A. |last7=Matz |first7=M. V. |date=2002-04-02 |title=Diversity and evolution of the green fluorescent protein family |journal=Proceedings of the National Academy of Sciences |volume=99 |issue=7 |pages=4256–4261 |doi=10.1073/pnas.062552299 |doi-access=free |issn=0027-8424 |pmc=123635 |pmid=11929996|bibcode=2002PNAS...99.4256L }}][{{Cite journal |last1=Alieva |first1=Naila O. |last2=Konzen |first2=Karen A. |last3=Field |first3=Steven F. |last4=Meleshkevitch |first4=Ella A. |last5=Hunt |first5=Marguerite E. |last6=Beltran-Ramirez |first6=Victor |last7=Miller |first7=David J. |last8=Wiedenmann |first8=Jörg |last9=Salih |first9=Anya |last10=Matz |first10=Mikhail V. |display-authors=6 |date=2008-07-16 |editor-last=El-Shemy |editor-first=Hany A. |title=Diversity and Evolution of Coral Fluorescent Proteins |journal=PLOS ONE |language=en |volume=3 |issue=7 |article-number=e2680 |doi=10.1371/journal.pone.0002680 |doi-access=free |issn=1932-6203 |pmc=2481297 |pmid=18648549|bibcode=2008PLoSO...3.2680A }}][{{Cite journal |last1=Chudakov |first1=Dmitriy M. |last2=Matz |first2=Mikhail V. |last3=Lukyanov |first3=Sergey |last4=Lukyanov |first4=Konstantin A. |date=July 2010 |title=Fluorescent Proteins and Their Applications in Imaging Living Cells and Tissues |url=https://www.physiology.org/doi/10.1152/physrev.00038.2009 |journal=Physiological Reviews |volume=90 |issue=3 |pages=1103–1163 |doi=10.1152/physrev.00038.2009 |pmid=20664080 |issn=0031-9333|url-access=subscription }}]
== Taxonomic range ==
=== Plants ===
Biofluorescence is frequent in plants, and can occur in many of their parts.[{{Cite journal |last=Holovachov |first=Oleksandr |date=2015-09-02 |title=Unseen beauty of flowers – hidden signals or spectacular by-product? |url=http://www.tandfonline.com/doi/full/10.1080/14688417.2015.1078121 |journal=Green Letters |volume=19 |issue=3 |pages=329–331 |doi=10.1080/14688417.2015.1078121 |issn=1468-8417}}] The biofluorescence in chlorophyll but has been studied since the 1800s.[{{Cite journal |last1=Lagorio |first1=M. Gabriela |last2=Cordon |first2=Gabriela B. |last3=Iriel |first3=Analia |date=September 2015 |title=Reviewing the relevance of fluorescence in biological systems |url=https://link.springer.com/10.1039/c5pp00122f |journal=Photochemical & Photobiological Sciences |language=en |volume=14 |issue=9 |pages=1538–1559 |doi=10.1039/c5pp00122f |issn=1474-905X|hdl=11336/8072 |hdl-access=free }}] Generally, [chlorophyll](/source/chlorophyll) [fluoresces](/source/Chlorophyll_fluorescence) red,[{{Cite journal |last1=Murchie |first1=E.H. |last2=Lawson |first2=T. |date=October 2013 |title=Chlorophyll fluorescence analysis: a guide to good practice and understanding some new applications |url=https://academic.oup.com/jxb/article-lookup/doi/10.1093/jxb/ert208 |journal=Journal of Experimental Botany |volume=64 |issue=13 |pages=3983–3998 |doi=10.1093/jxb/ert208 |pmid=23913954 |issn=1460-2431|url-access=subscription }}] and can be used as a measure of [photosynthetic](/source/Photosynthesis) capabilities,[{{Cite journal |last1=Krause |first1=G. Heinrich |last2=Weis |first2=Engelbert |date=1984 |title=Chlorophyll fluorescence as a tool in plant physiology: II. Interpretation of fluorescence signals |url=http://link.springer.com/10.1007/BF00028527 |journal=Photosynthesis Research |language=en |volume=5 |issue=2 |pages=139–157 |doi=10.1007/BF00028527 |pmid=24458602 |issn=0166-8595|url-access=subscription }}][{{Cite journal |last=Roshchina |first=Victoria V. |date=2012-09-10 |title=Vital Autofluorescence: Application to the Study of Plant Living Cells |journal=International Journal of Spectroscopy |volume=2012 |pages=1–14 |doi=10.1155/2012/124672 |doi-access=free |issn=1687-9449}}][{{Cite journal |last1=Mori |first1=Shinnosuke |last2=Fukui |first2=Hiroshi |last3=Oishi |first3=Masanori |last4=Sakuma |first4=Masayuki |last5=Kawakami |first5=Mari |last6=Tsukioka |first6=Junko |last7=Goto |first7=Katsumi |last8=Hirai |first8=Nobuhiro |date=2018-06-01 |title=Biocommunication between Plants and Pollinating Insects through Fluorescence of Pollen and Anthers |journal=Journal of Chemical Ecology |volume=44 |issue=6 |pages=591–600 |doi=10.1007/s10886-018-0958-9 |pmid=29717395 |bibcode=2018JCEco..44..591M |issn=1573-1561}}] [anthers](/source/Stamen) [{{Cite journal |last1=Gandía-Herrero |first1=Fernando |last2=García-Carmona |first2=Francisco |last3=Escribano |first3=Josefa |date=September 2005 |title=Floral fluorescence effect |url=https://www.nature.com/articles/437334a |journal=Nature |language=en |volume=437 |issue=7057 |page=334 |doi=10.1038/437334a |pmid=16163341 |issn=0028-0836}}] may also fluoresce. These characters may produce a variety of colors depending on the [pigment](/source/pigment) responsible for fluorescence.[{{Cite journal |last=Gumbert |first=A. |date=2000-06-01 |title=Color choices by bumble bees (Bombus terrestris): innate preferences and generalization after learning |journal=Behavioral Ecology and Sociobiology |language=en |volume=48 |issue=1 |pages=36–43 |doi=10.1007/s002650000213 |issn=1432-0762}}][{{Cite journal |last1=Kurup |first1=R. |last2=Johnson |first2=A. J. |last3=Sankar |first3=S. |last4=Hussain |first4=A. A. |last5=Kumar |first5=C. Sathish |last6=Sabulal |first6=B. |date=May 2013 |editor-last=Rennenberg |editor-first=H. |title=Fluorescent prey traps in carnivorous plants |url=https://onlinelibrary.wiley.com/doi/10.1111/j.1438-8677.2012.00709.x |journal=Plant Biology |volume=15 |issue=3 |pages=611–615 |doi=10.1111/j.1438-8677.2012.00709.x |pmid=23696970 |bibcode=2013PlBio..15..611K |issn=1435-8603|url-access=subscription }}] or serve no function.[{{Cite journal |last1=Lamb |first1=Jennifer Y. |last2=Davis |first2=Matthew P. |date=2020-02-27 |title=Salamanders and other amphibians are aglow with biofluorescence |journal=Scientific Reports |language=en |volume=10 |issue=1 |page=2821 |doi=10.1038/s41598-020-59528-9 |issn=2045-2322 |pmc=7046780 |pmid=32108141|bibcode=2020NatSR..10.2821L }}][{{Cite journal |last1=Santa-Cruz |first1=Roy |last2=von May |first2=Rudolf |last3=Catenazzi |first3=Alessandro |last4=Whitcher |first4=Courtney |last5=López Tejeda |first5=Evaristo |last6=Rabosky |first6=Daniel |date=2019-08-26 |title=A New Species of Terrestrial-Breeding Frog (Amphibia, Strabomantidae, Noblella) from the Upper Madre De Dios Watershed, Amazonian Andes and Lowlands of Southern Peru |journal=Diversity |language=en |volume=11 |issue=9 |page=145 |doi=10.3390/d11090145 |doi-access=free |issn=1424-2818}}][{{Cite journal |last1=Whitcher |first1=Courtney |last2=Beaver |first2=Lilyanne |last3=Lemmon |first3=Emily Moriarty |date=February 2024 |title=The effect of biofluorescence on predation upon Cope's gray treefrog: A clay model experiment |url=https://linkinghub.elsevier.com/retrieve/pii/S0376635724000111 |journal=Behavioural Processes |language=en |volume=215 |article-number=104996 |doi=10.1016/j.beproc.2024.104996|url-access=subscription }}] fish,[{{Cite journal |last1=Pearn |first1=Sophie M. |last2=Bennett |first2=Andrew T.D. |last3=Cuthill |first3=Innes C. |date=2001-11-07 |title=Ultraviolet vision, fluorescence and mate choice in a parrot, the budgerigar Melopsittacus undulatus |journal=Proceedings of the Royal Society of London. Series B: Biological Sciences |language=en |volume=268 |issue=1482 |pages=2273–2279 |doi=10.1098/rspb.2001.1813 |issn=0962-8452 |pmc=1088876 |pmid=11674876}}][{{Cite journal |last1=Hausmann |first1=Franziska |last2=Arnold |first2=Kathryn E. |last3=Marshall |first3=N. Justin |last4=Owens |first4=Ian P. F. |date=2003-01-07 |title=Ultraviolet signals in birds are special |journal=Proceedings of the Royal Society of London. Series B: Biological Sciences |language=en |volume=270 |issue=1510 |pages=61–67 |doi=10.1098/rspb.2002.2200 |issn=0962-8452 |pmc=1691211 |pmid=12590772}}][{{Cite report |url=https://figshare.utas.edu.au/articles/journal_contribution/Update_on_fluorescent_mammals_and_birds_in_Tasmania/25131257/1 |title=Update on fluorescent mammals and birds in Tasmania |last=Gershwin |first=Lisa-ann |date=2024-02-05 |doi=10.26749/25131257.v1}}] and mammals.[{{Cite journal |last1=Anich |first1=Paula Spaeth |last2=Anthony |first2=Sharon |last3=Carlson |first3=Michaela |last4=Gunnelson |first4=Adam |last5=Kohler |first5=Allison M. |last6=Martin |first6=Jonathan G. |last7=Olson |first7=Erik R. |date=2021-03-26 |title=Biofluorescence in the platypus ( Ornithorhynchus anatinus ) |url=https://www.degruyter.com/document/doi/10.1515/mammalia-2020-0027/html |journal=Mammalia |language=en |volume=85 |issue=2 |pages=179–181 |doi=10.1515/mammalia-2020-0027 |issn=1864-1547}}][{{Cite journal |last1=Olson |first1=Erik R. |last2=Carlson |first2=Michaela R. |last3=Ramanujam |first3=V. M. Sadagopa |last4=Sears |first4=Lindsay |last5=Anthony |first5=Sharon E. |last6=Anich |first6=Paula Spaeth |last7=Ramon |first7=Leigh |last8=Hulstrand |first8=Alissa |last9=Jurewicz |first9=Michaela |last10=Gunnelson |first10=Adam S. |last11=Kohler |first11=Allison M. |last12=Martin |first12=Jonathan G. |date=2021-02-18 |title=Vivid biofluorescence discovered in the nocturnal Springhare (Pedetidae) |journal=Scientific Reports |language=en |volume=11 |issue=1 |page=4125 |doi=10.1038/s41598-021-83588-0 |issn=2045-2322 |pmc=7892538 |pmid=33603032|bibcode=2021NatSR..11.4125O }}][{{Cite journal |last1=Matz |first1=Mikhail V. |last2=Marshall |first2=N. Justin |last3=Vorobyev |first3=Misha |date=2006 |title=Are Corals Colorful? |url=https://onlinelibrary.wiley.com/doi/10.1562/2005-08-18-RA-653 |journal=Photochemistry and Photobiology |language=en |volume=82 |issue=2 |pages=345–350 |doi=10.1562/2005-08-18-RA-653 |pmid=16613484 |issn=0031-8655|url-access=subscription }}]), attracting mates (e.g. birds[{{Cite journal |last1=Hausmann |first1=Franziska |last2=Arnold |first2=Kathryn E. |last3=Marshall |first3=N. Justin |last4=Owens |first4=Ian P. F. |date=2003 |title=Ultraviolet signals in birds are special |journal=Proceedings of the Royal Society of London. Series B: Biological Sciences |volume=270 |issue=1510 |pages=61–67 |doi=10.1098/rspb.2002.2200 |issn=0962-8452 |pmc=1691211 |pmid=12590772}}] and copepods[{{Cite journal |last1=Shagin |first1=Dmitry A. |last2=Barsova |first2=Ekaterina V. |last3=Yanushevich |first3=Yurii G. |last4=Fradkov |first4=Arkady F. |last5=Lukyanov |first5=Konstantin A. |last6=Labas |first6=Yulii A. |last7=Semenova |first7=Tatiana N. |last8=Ugalde |first8=Juan A. |last9=Meyers |first9=Ann |last10=Nunez |first10=Jose M. |last11=Widder |first11=Edith A. |last12=Lukyanov |first12=Sergey A. |last13=Matz |first13=Mikhail V. |display-authors=6 |date=2004 |title=GFP-like Proteins as Ubiquitous Metazoan Superfamily: Evolution of Functional Features and Structural Complexity |url=https://academic.oup.com/mbe/article-lookup/doi/10.1093/molbev/msh079 |journal=Molecular Biology and Evolution |volume=21 |issue=5 |pages=841–850 |doi=10.1093/molbev/msh079 |pmid=14963095 |issn=1537-1719|url-access=subscription }}]) and symbionts (e.g. corals[{{Cite journal |last1=Strader |first1=Marie E. |last2=Aglyamova |first2=Galina V. |last3=Matz |first3=Mikhail V. |date=January 2016 |title=Red fluorescence in coral larvae is associated with a diapause-like state |url=https://onlinelibrary.wiley.com/doi/10.1111/mec.13488 |journal=Molecular Ecology |language=en |volume=25 |issue=2 |pages=559–569 |doi=10.1111/mec.13488 |pmid=26600127 |bibcode=2016MolEc..25..559S |issn=0962-1083|url-access=subscription }}]
== Evolution ==
Most likely biofluorescence arose multiple times by [convergent evolution](/source/convergent_evolution).[{{Cite journal |last1=Ugalde |first1=Juan A. |last2=Chang |first2=Belinda S. W. |last3=Matz |first3=Mikhail V. |date=2004-09-03 |title=Evolution of Coral Pigments Recreated |url=https://www.science.org/doi/10.1126/science.1099597 |journal=Science |volume=305 |issue=5689 |page=1433 |doi=10.1126/science.1099597 |pmid=15353795 |issn=0036-8075|url-access=subscription }}] Reconstruction experiments suggest the original fluorescent protein was green, and had a simple beta-barrel shape with a [chromophore](/source/chromophore) hidden inside. Different colors of [green fluorescent protein](/source/green_fluorescent_protein)s (GFP), yellow, red, cyan, and amber, are determined by variations in chromophore structure. Red fluorescent proteins chromophore are the most complex and require extra maturation steps. New fluorescent proteins evolved through [gene duplication](/source/gene_duplication) and accumulation of multiple mutations which gradually changed autocatalytic functions and final chromophore structure.[{{Cite journal |last1=Kumagai |first1=Akiko |last2=Ando |first2=Ryoko |last3=Miyatake |first3=Hideyuki |last4=Greimel |first4=Peter |last5=Kobayashi |first5=Toshihide |last6=Hirabayashi |first6=Yoshio |last7=Shimogori |first7=Tomomi |last8=Miyawaki |first8=Atsushi |display-authors=6 |date=June 2013 |title=A Bilirubin-Inducible Fluorescent Protein from Eel Muscle |url=https://linkinghub.elsevier.com/retrieve/pii/S0092867413006442 |journal=Cell |volume=153 |issue=7 |pages=1602–1611 |doi=10.1016/j.cell.2013.05.038|pmid=23768684 |doi-access=free }}] UnaG absorbs blue light and emits green only when the complex with bilirubin is formed. This feature makes UnaG attractive for biomedical assays in exploration of bilirubin-dependent [cellular processes](/source/cellular_processes).[{{Cite journal |last1=Yeh |first1=Johannes T.-H. |last2=Nam |first2=Kwangho |last3=Yeh |first3=Joshua T.-H. |last4=Perrimon |first4=Norbert |date=2017-02-08 |title=eUnaG: a new ligand-inducible fluorescent reporter to detect drug transporter activity in live cells |journal=Scientific Reports |volume=7 |issue=1 |article-number=41619 |doi=10.1038/srep41619 |issn=2045-2322 |pmc=5296874 |pmid=28176814|bibcode=2017NatSR...741619Y }}]
Another non-GFP-like fluorescent protein is a blue protein, sandercyanin, from [freshwater fish](/source/freshwater_fish) walleye, ''[Sander vitreus](/source/Walleye),'' in the North hemisphere. Sandercyanin is seasonally produced, with production peaking in the late summer, and is thought to be a defense against high UV. Sandercyanin binds [biliverdin IXa](/source/Biliverdin), and together they form a tetra-homomer which absorbs UV light at 375 nm and emits red light at 675 nm.[{{Cite journal |last1=Ghosh |first1=Swagatha |last2=Yu |first2=Chi-Li |last3=Ferraro |first3=Daniel J. |last4=Sudha |first4=Sai |last5=Pal |first5=Samir Kumar |last6=Schaefer |first6=Wayne F. |last7=Gibson |first7=David T. |last8=Ramaswamy |first8=S. |display-authors=6 |date=2016-10-11 |title=Blue protein with red fluorescence |journal=Proceedings of the National Academy of Sciences |volume=113 |issue=41 |pages=11513–11518 |doi=10.1073/pnas.1525622113 |doi-access=free |issn=0027-8424 |pmc=5068307 |pmid=27688756|bibcode=2016PNAS..11311513G }}]
Two species of [catsharks](/source/Scyliorhinidae), ''[Cephaloscyllium ventriosum](/source/Swell_shark),'' endemic to the eastern Pacific, and ''[Scyliorhinus retifer](/source/Chain_catshark),'' from the western Atlantic, fluoresce by a different mechanism.[{{Cite journal |last1=Park |first1=Hyun Bong |last2=Lam |first2=Yick Chong |last3=Gaffney |first3=Jean P. |last4=Weaver |first4=James C. |last5=Krivoshik |first5=Sara Rose |last6=Hamchand |first6=Randy |last7=Pieribone |first7=Vincent |last8=Gruber |first8=David F. |last9=Crawford |first9=Jason M. |display-authors=6 |date=September 2019 |title=Bright Green Biofluorescence in Sharks Derives from Bromo-Kynurenine Metabolism |journal=iScience |volume=19 |pages=1291–1336 |doi=10.1016/j.isci.2019.07.019 |pmc=6831821 |pmid=31402257|bibcode=2019iSci...19.1291P }}] The fluorescence is produced by brominated tryptophan-kynurenine metabolites, small [aromatic compounds](/source/aromatic_compounds) present in the lighter-colored regions of skin on the fish. Dermal features of the shark skin optically enhance the fluorescent signal.