Editing Biophoton (section)

== Proposed physical mechanisms ==

Chemi-excitation via [[oxidative stress]] by [[reactive oxygen species]] or [[catalysis]] by [[enzymes]] (i.e., [[peroxidase]], [[lipoxygenase]]) is a common event in the biomolecular [[wikt:milieu|milieu]].<ref name=pmid7635351>{{cite journal | vauthors = Cilento G, Adam W | title = From free radicals to electronically excited species | journal = Free Radical Biology & Medicine | volume = 19 | issue = 1 | pages = 103–14 | date = July 1995 | pmid = 7635351 | doi = 10.1016/0891-5849(95)00002-F }}</ref> Such reactions can lead to the formation of [[Spin triplet|triplet]] excited species, which release [[photons]] upon returning to a lower [[energy level]] in a process analogous to [[phosphorescence]]. That this process is a contributing factor to spontaneous biophoton emission has been indicated by studies demonstrating that biophoton emission can be increased by depleting assayed tissue of [[antioxidants]]<ref name=pmid2801215>{{cite journal | vauthors = Ursini F, Barsacchi R, Pelosi G, Benassi A | title = Oxidative stress in the rat heart, studies on low-level chemiluminescence | journal = Journal of Bioluminescence and Chemiluminescence | volume = 4 | issue = 1 | pages = 241–4 | date = July 1989 | pmid = 2801215 | doi = 10.1002/bio.1170040134 }}</ref> or by addition of carbonyl derivatizing agents.<ref name=pmid11467852>{{cite journal | vauthors = Kataoka Y, Cui Y, Yamagata A, Niigaki M, Hirohata T, Oishi N, Watanabe Y | title = Activity-dependent neural tissue oxidation emits intrinsic ultraweak photons | journal = Biochemical and Biophysical Research Communications | volume = 285 | issue = 4 | pages = 1007–11 | date = July 2001 | pmid = 11467852 | doi = 10.1006/bbrc.2001.5285 }}</ref> Further support is provided by studies indicating that emission can be increased by addition of [[reactive oxygen species]].<ref name=pmid6928628>{{cite journal | vauthors = Boveris A, Cadenas E, Reiter R, Filipkowski M, Nakase Y, Chance B | title = Organ chemiluminescence: noninvasive assay for oxidative radical reactions | journal = Proceedings of the National Academy of Sciences of the United States of America | volume = 77 | issue = 1 | pages = 347–51 | date = January 1980 | pmid = 6928628 | pmc = 348267 | doi = 10.1073/pnas.77.1.347 | bibcode = 1980PNAS...77..347B | doi-access = free }}</ref>

===Plants===
Imaging of biophotons from leaves has been used as a method for assaying R gene responses.<ref name="Biophoton imaging: a nondestructive"/> These genes and their associated proteins are responsible for [[pathogen]] recognition and activation of defense signaling networks leading to the hypersensitive response,<ref>{{cite journal | vauthors = Iniguez AL, Dong Y, Carter HD, Ahmer BM, Stone JM, Triplett EW | title = Regulation of enteric endophytic bacterial colonization by plant defenses | journal = Molecular Plant-Microbe Interactions | volume = 18 | issue = 2 | pages = 169–78 | date = February 2005 | pmid = 15720086 | doi = 10.1094/MPMI-18-0169 | doi-access = free }}</ref> which is one of the mechanisms of the resistance of plants to pathogen infection. It involves the generation of reactive oxygen species (ROS), which have crucial roles in [[signal transduction]] or as toxic agents leading to cell death.<ref>{{cite journal | vauthors = Kobayashi M, Sasaki K, Enomoto M, Ehara Y | title = Highly sensitive determination of transient generation of biophotons during hypersensitive response to cucumber mosaic virus in cowpea | journal = Journal of Experimental Botany | volume = 58 | issue = 3 | pages = 465–72 | year = 2006 | pmid = 17158510 | doi = 10.1093/jxb/erl215 | doi-access = free }}</ref>

Biophotons have been also observed in the roots of stressed plants. In healthy cells, the concentration of ROS is minimized by a system of biological antioxidants. However, heat shock and other stresses changes the equilibrium between oxidative stress and antioxidant activity, for example, the rapid rise in temperature induces biophoton emission by ROS.<ref>{{cite journal | vauthors = Kobayashi K, Okabe H, Kawano S, Hidaka Y, Hara K | title = Biophoton emission induced by heat shock | journal = PLOS ONE | volume = 9 | issue = 8 | pages = e105700 | year = 2014 | pmid = 25153902 | pmc = 4143285 | doi = 10.1371/journal.pone.0105700 | bibcode = 2014PLoSO...9j5700K | doi-access = free }}</ref>

===Hypothesized involvement in cellular communication===
In the 1920s, the Russian embryologist [[Alexander Gurwitsch]] reported "ultraweak" photon emissions from living tissues in the UV-range of the spectrum. He named them "mitogenetic rays" because his experiments convinced him that they had a stimulating effect on [[cell division]].<ref name=pmid3294029>{{cite journal | vauthors = Gurwitsch AA | title = A historical review of the problem of mitogenetic radiation | journal = Experientia | volume = 44 | issue = 7 | pages = 545–50 | date = July 1988 | pmid = 3294029 | doi = 10.1007/bf01953301 | s2cid = 10930945 }}</ref>

In the 1970s [[Fritz-Albert Popp]] and his research group at the [[University of Marburg]] ([[Germany]]) showed that the spectral distribution of the emission fell over a wide range of wavelengths, from 200 to 750&nbsp;nm.<ref>{{cite journal | vauthors = Wijk RV, Wijk EP | title = An Introduction to Human Biophoton Emission| journal = Forschende Komplementärmedizin und Klassische Naturheilkunde | volume = 12 | issue = 2 | pages = 77–83 | date = April 2005 | pmid = 15947465 | doi = 10.1159/000083763 | s2cid = 25794113 }}</ref>  Popp's work on the biophoton emission's statistical properties, namely the claims on its coherence, was criticised for lack of scientific rigour.<ref name="coherence"/>

One biophoton mechanism focuses on injured cells that are under higher levels of [[oxidative stress]], which is one source of light, and can be deemed to constitute a "distress signal" or background chemical process, but this mechanism is yet to be demonstrated.{{citation needed|date=February 2020}} The difficulty of teasing out the effects of any supposed biophotons amid the other numerous chemical interactions between cells makes it difficult to devise a testable hypothesis. A 2010 review article discusses various published theories on this kind of signaling.<ref name=pmid20674588>{{cite journal | vauthors = Cifra M, Fields JZ, Farhadi A | title = Electromagnetic cellular interactions | journal = Progress in Biophysics and Molecular Biology | volume = 105 | issue = 3 | pages = 223–46 | date = May 2011 | pmid = 20674588 | doi = 10.1016/j.pbiomolbio.2010.07.003 }}</ref>

The hypothesis of cellular communication by biophotons was highly criticised for failing to explain how could cells detect photonic signals several orders of magnitude weaker than the natural background illumination.<ref name="communication">{{cite journal | vauthors = Kučera O, Cifra M | title = Cell-to-cell signaling through light: just a ghost of chance? | journal = Cell Communication and Signaling | volume = 11 | issue = 87 | pages = 87 | date = November 2013 | pmid = 24219796 | doi = 10.1186/1478-811X-11-87 | pmc = 3832222 | doi-access = free }}</ref>