View source for Photobiology

{{Short description|Scientific study of light's effect on living organisms}}
'''Photobiology''' is the scientific study of the beneficial and harmful interactions of [[light]] (technically, [[non-ionizing radiation]]) in living [[organism]]s.<ref name=":2">{{cite web |author=Smith, Kendrick C.  |year=2014 |url=http://www.photobiology.info/introduction.html |title=What Is Photobiology? |accessdate=2018-08-02 }}</ref> The field includes the study of photophysics, photochemistry, [[photosynthesis]], [[photomorphogenesis]], [[visual system|visual processing]], [[circadian rhythm]]s, photomovement, [[bioluminescence]], and [[ultraviolet]] radiation effects.<ref>{{Cite book|url=https://books.google.com/books?id=EGfSBwAAQBAJ&dq=photobiology&pg=PA2|title=The Science of Photobiology|last=Smith|first=Kendric|date=2013-03-08|publisher=Springer Science & Business Media|isbn=9781461580614}}</ref>

The division between [[ionizing radiation]] and non-ionizing radiation is typically considered to be a photon energy greater than 10 eV,<ref>{{cite web |url=http://transition.fcc.gov/Bureaus/Engineering_Technology/Documents/bulletins/oet56/oet56e4.pdf |accessdate=2018-08-02 |url-status=live |archiveurl=https://web.archive.org/web/20111020131849/http://transition.fcc.gov/Bureaus/Engineering_Technology/Documents/bulletins/oet56/oet56e4.pdf |archivedate=2011-10-20 |author1=Robert F. Cleveland, Jr. |author2=Jerry L. Ulcek |title=Questions and Answers about Biological Effects and Potential Hazards of Radiofrequency Electromagnetic Fields |publisher=OET (Office of Engineering and Technology) Federal Communications Commission |location=Washington, D.C. |edition=4th |date=August 1999}}</ref> which approximately corresponds to both the first ionization energy of oxygen, and the ionization energy of hydrogen at about 14 eV.<ref>{{cite web |author=Jim Clark |year=2000 |url=http://www.chemguide.co.uk/atoms/properties/ies.html |title=Ionisation Energy |accessdate=2018-08-02 |url-status=live |archiveurl=https://web.archive.org/web/20111126131813/http://www.chemguide.co.uk/atoms/properties/ies.html |archivedate=2011-11-26}}</ref>

When [[photon]]s come into contact with molecules, these molecules can absorb the energy in photons and become excited. Then they can react with molecules around them and stimulate "[[Photochemistry|photochemical]]" and "photophysical" changes of molecular structures.<ref name=":2" />

== Photophysics<ref name=":3">{{Cite web|url=http://photobiology.info/Visser-Rolinski.html|title=BASIC PHOTOPHYSICS|website=photobiology.info|access-date=2019-11-24}}</ref> ==
This area of Photobiology focuses on the physical interactions of light and matter. When molecules absorb photons that matches their energy requirements they promote a valence electron from a ground state to an excited state and they become a lot more reactive. This is an extremely fast process, but very important for different processes.<ref name=":3" />

== Photochemistry<ref>{{Cite web|url=http://photobiology.info/Photochem.html|title=BASIC PHOTOCHEMISTRY|website=photobiology.info|access-date=2019-11-24}}</ref> ==
This area of Photobiology studies the reactivity of a molecule when it absorbs energy that comes from light. It also studies what happens with this energy, it could be given off as heat or fluorescence so the molecule goes back to ground state.

There are 3 basic laws of '''photochemistry:'''

'''1) First Law of Photochemistry:''' This law explains that in order for photochemistry to happen, light has to be absorbed.

'''2) Second Law of Photochemistry:''' This law explains that only one molecule will be activated by each photon that is absorbed.

'''3) Bunsen-Roscoe Law of Reciprosity:''' This law explains that the energy in the final products of a photochemical reaction will be directly proportional to the total energy that was initially absorbed by the system.

== Plant Photobiology ==
Plant growth and development is highly dependent on [[light]]. [[Photosynthesis]] is one of the most important biochemical processes for life on earth and its possible only due to the ability of plants to use energy from photons and convert it into molecules such as [[Nicotinamide adenine dinucleotide phosphate|NADPH]] and [[Adenosine triphosphate|ATP]], to then fix [[carbon dioxide]] and make it into sugars that plants can use for their growth and development.<ref name=":1">{{Cite journal|last1=Eichhorn Bilodeau|first1=Samuel|last2=Wu|first2=Bo-Sen|last3=Rufyikiri|first3=Anne-Sophie|last4=MacPherson|first4=Sarah|last5=Lefsrud|first5=Mark|date=2019-03-29|title=An Update on Plant Photobiology and Implications for Cannabis Production|journal=Frontiers in Plant Science|volume=10|page=296|doi=10.3389/fpls.2019.00296|pmid=31001288|pmc=6455078|issn=1664-462X|doi-access=free}}</ref> But photosynthesis is not the only plant process driven by light, other processes such as [[Photomorphogenesis|photomorphology]] and plant [[Photoperiodism|photoperiod]] are extremely important for regulation of vegetative and reproductive growth as well as production of plant [[secondary metabolite]]s.<ref>{{Cite journal|last1=Lefsrud|first1=Mark G.|last2=Kopsell|first2=Dean A.|last3=Sams|first3=Carl E.|date=December 2008|title=Irradiance from Distinct Wavelength Light-emitting Diodes Affect Secondary Metabolites in Kale|journal=HortScience|volume=43|issue=7|pages=2243–2244|doi=10.21273/hortsci.43.7.2243|issn=0018-5345|doi-access=free}}</ref>

=== Photosynthesis ===
Photosynthesis is defined as a series of biochemical reactions that phototrophic cells perform to transform light energy to chemical energy and store it in carbon-carbon bonds of [[carbohydrate]]s.<ref name=":0">{{Cite book|title=The cell : a molecular approach|last=Cooper, Geoffrey M..|isbn=9781605357072|oclc=1085300153|year = 2018}}</ref> As it is widely known, this process happens inside of the [[chloroplast]] of photosynthetic plant cells where light absorbing [[Biological pigment|pigments]] can be found embedded in the membranes of structures called [[thylakoid]]s.<ref name=":0" /> There are 2 main pigments present in the [[Photosystem]]s of [[Vascular plant|higher plants]]: [[chlorophyll]] (a or b) and [[carotene]]s.<ref name=":1" /> These pigments are organized to maximize the light reception and transfer, and they absorb specific [[wavelength]]s to broaden the amount of light that can be captured and used for photo-[[Redox|redox reactions]].<ref name=":1" />

==== Photosynthetically Active Radiation (PAR) ====
{{main|Photosynthetically active radiation}}

Due to the limited amount of pigments in plant photosynthetic cells, there is a limited range of wavelengths that plants can use to perform photosynthesis. This range is called "Photosynthetically Active Radiation (PAR)". This range is interestingly almost the same as the human visible spectrum and it extends in wavelengths from approximately 400-700&nbsp;nm.<ref>{{Cite journal|last=McCree|first=K.J.|date=January 1971|title=The action spectrum, absorptance and quantum yield of photosynthesis in crop plants|journal=Agricultural Meteorology|volume=9|pages=191–216|doi=10.1016/0002-1571(71)90022-7|issn=0002-1571}}</ref> PAR is measured in μmol s<sup>−1</sup>m<sup>−2</sup>  and it measures the rate and intensity of radiant light in terms of micro-moles per unit of surface area and time that plants can use for photosynthesis.<ref>{{Cite journal|last=Young|first=Andrew John|date=December 1991|title=The photoprotective role of carotenoids in higher plants|journal=Physiologia Plantarum|volume=83|issue=4|pages=702–708|doi=10.1034/j.1399-3054.1991.830426.x|issn=0031-9317}}</ref>

==== Photobiologically Active Radiation (PBAR) ====
Photobiologically Active Radiation (PBAR) is a range of light energy beyond and including [[Photosynthetically active radiation|PAR]]. Photobiological Photon Flux (PBF) is the metric used to measure PBAR.

=== Photomorphogenesis ===
This process refers to the development of the morphology of plants which is light-mediated and controlled by 5 distinct photoreceptors: UVR8, Cryptochrome, Phototropin, Phytochrome r and Phytochrome fr.<ref>{{Cite journal|last=Pocock|first=Tessa|date=September 2015|title=Light-emitting Diodes and the Modulation of Specialty Crops: Light Sensing and Signaling Networks in Plants|journal=HortScience|volume=50|issue=9|pages=1281–1284|doi=10.21273/hortsci.50.9.1281|issn=0018-5345|doi-access=free}}</ref> Light can control morphogenic processes such as leaf size and shoot elongation.

Different wavelengths of light produce different changes in plants.<ref>{{cite web |last1=Scandola PhD |first1=Sabine |title=Photobiology: Plant Light Matters |url=https://g2voptics.com/photobiology/ |publisher=G2V Optics}}</ref> Red to Far Red light for example, regulates stem growth and straightening of the seedling shoots that are coming out of the ground.<ref>{{Cite journal|last1=McNellis|first1=Timothy W.|last2=Deng|first2=Xing-Wang|date=November 1995|title=Light Control of Seedling Morphogenetic Pattern|journal=The Plant Cell|volume=7|issue=11|pages=1749–1761|doi=10.2307/3870184|issn=1040-4651|jstor=3870184|pmid=8535132|pmc=161035}}</ref> Some studies also claim that red and far red light increases the rooting mass of tomatoes<ref>{{Cite journal|last1=Vu|first1=Ngoc-Thang|last2=Kim|first2=Young-Shik|last3=Kang|first3=Ho-Min|last4=Kim|first4=Il-Seop|date=February 2014|title=Influence of short-term irradiation during pre- and post-grafting period on the graft-take ratio and quality of tomato seedlings|journal=Horticulture, Environment, and Biotechnology|volume=55|issue=1|pages=27–35|doi=10.1007/s13580-014-0115-5|s2cid=16250222|issn=2211-3452}}</ref>  as well as the rooting percentage of grape plants.<ref>{{Cite journal|last1=Poudel|first1=Puspa Raj|last2=Kataoka|first2=Ikuo|last3=Mochioka|first3=Ryosuke|date=2007-11-30|title=Effect of red- and blue-light-emitting diodes on growth and morphogenesis of grapes|journal=Plant Cell, Tissue and Organ Culture|volume=92|issue=2|pages=147–153|doi=10.1007/s11240-007-9317-1|s2cid=24671493|issn=0167-6857}}</ref> On the other hand, blue and UV light regulate the germination and elongation of the plant as well as other physiological processes such as stomatal control<ref>{{Cite journal|last1=Schwartz|first1=A.|last2=Zeiger|first2=E.|date=May 1984|title=Metabolic energy for stomatal opening. Roles of photophosphorylation and oxidative phosphorylation|journal=Planta|volume=161|issue=2|pages=129–136|doi=10.1007/bf00395472|pmid=24253600|s2cid=12539218|issn=0032-0935}}</ref> and responses to environmental stress.<ref>{{Cite journal|last1=Goins|first1=G.D.|last2=Yorio|first2=N.C.|last3=Sanwo|first3=M.M.|last4=Brown|first4=C.S.|date=1997|title=Photomorphogenesis, photosynthesis, and seed yield of wheat plants grown under red light-emitting diodes (LEDs) with and without supplemental blue lighting|journal=Journal of Experimental Botany|volume=48|issue=7|pages=1407–1413|doi=10.1093/jxb/48.7.1407|pmid=11541074|issn=0022-0957|doi-access=free}}</ref> Finally, green light was thought not to be available to plants due to the lack of pigments that would absorb this light. However, in 2004 it was found that green light can influence stomatal activity, stem elongation of young plants and leaf expansion.<ref>{{Cite book|title=Green Light Stimulates Early Stem Elongation, Antagonizing Light-Mediated Growth Inhibition1|last=Folta, Kevin M.|authorlink=Kevin Folta|date=July 2004|publisher=American Society of Plant Biologists|oclc=678171603}}</ref>

=== Secondary Plant Metabolites ===
These compounds are chemicals that plants produce as part of their biochemical processes and help them perform certain functions as well as protect themselves from different environmental factors. In this case, some metabolites such as anthocyanins, flavonoids, and carotenes, can accumulate in plant tissues to protect them from UV radiation and very high light intensity<ref>{{Cite book|title=Non-Photochemical Quenching and Energy Dissipation in Plants, Algae and Cyanobacteria|last=Demmig-Adams, Barbara.|isbn=978-94-017-9032-1|oclc=1058692723|date = 2014-11-22}}</ref>

==Photobiologists==
* [[Thomas Patrick Coohill]], former president of the [[American Society for Photobiology]]
* [[Harold F. Blum]], who explored sunlight-induced [[skin cancer]]
*[[Paul Bert]], 1878 photobiology pioneer

==See also==
{{columns-list|colwidth=30em|
*[[Ecological light pollution]]
*[[Light effects on circadian rhythm]]
* [[Light therapy]]
*[[Photobiomodulation]]
*''[[Photochemical and Photobiological Sciences]]''
*[[Photoperiodism]]
*[[Scotobiology]]
}}

==References==
<references />

==External links==
* {{url | http://photobiology.org/ | American Society for Photobiology}}
* {{url | http://www.photobiology.eu/ | European Society for Photobiology}}

{{Light Ethology}}
{{Branches of biology}}
{{Authority control}}

[[Category:Branches of biology]]
[[Category:Light]]