{{short description|Range of light at the extreme red end of the visible spectrum}} [[File:Linear visible spectrum.svg|thumb|500px|The visible spectrum; far-red is located at the far right.]] '''Far-red light''' is a range of light at the extreme red end of the visible spectrum, just before infrared light. Usually regarded as the region between 700 and 750 nm wavelength, it is dimly visible to human eyes. It is largely reflected or transmitted by plants because of the absorbance spectrum of chlorophyll, and it is perceived by the plant photoreceptor phytochrome. However, some organisms can use it as a source of energy in photosynthesis.<ref>{{Cite journal |last=Consoli |first=Giovanni |last2=Tufail |first2=Fiazall |last3=Leong |first3=Ho Fong |last4=Viola |first4=Stefania |last5=Davis |first5=Geoffry A. |last6=Rew |first6=Nicholas |last7=Medranda |first7=Daniel |last8=Hofer |first8=Michael |last9=Simpson |first9=Paul |last10=Sandrin |first10=Marco |last11=Chachuat |first11=Benoit |last12=Nelson |first12=Jenny |last13=Renger |first13=Thomas |last14=Murray |first14=James W. |last15=Fantuzzi |first15=Andrea |date=2025-12-11 |title=Locating the missing chlorophylls f in far-red photosystem I |url=https://www.science.org/doi/10.1126/science.ado6830 |journal=Science |language=en |volume=390 |issue=6778 |doi=10.1126/science.ado6830 |issn=0036-8075}}</ref><ref>{{cite journal | doi = 10.1016/j.bbabio.2005.05.005| pmid = 15950173| title = Photosynthetic activity of far-red light in green plants| journal = Biochimica et Biophysica Acta (BBA) - Bioenergetics| volume = 1708| issue = 3| pages = 311–21| year = 2005| last1 = Pettai| first1 = Hugo| last2 = Oja| first2 = Vello| last3 = Freiberg| first3 = Arvi| last4 = Laisk| first4 = Agu| doi-access = free}}</ref><ref>{{cite journal | doi = 10.1111/j.1399-3054.1969.tb07406.x| title = Adaptations in Pigment Composition and Photosynthesis by Far Red Radiation in Chlorella pyrenoidosa| journal = Physiologia Plantarum| volume = 22| issue = 3| pages = 516–528| year = 1969| last1 = Oquist| first1 = Gunnar| bibcode = 1969PPlan..22..516O}}</ref> Far-red light also is used for vision by certain organisms such as some species of deep-sea fishes<ref>{{cite journal | title = Dragon fish see using chlorophyll | doi = 10.1038/30871| year = 1998| last1 = Douglas| first1 = R. H.| journal = Nature| volume = 393| issue = 6684| page = 423| last2 = Partridge| first2 = J. C.| last3 = Dulai| first3 = K.| last4 = Hunt| first4 = D.| last5 = Mullineaux| first5 = C. W.| last6 = Tauber| first6 = A. Y.| last7 = Hynninen| first7 = P. H.| bibcode = 1998Natur.393..423D| s2cid = 4416089}}</ref><ref>{{cite news | title = Scientists Discover Unique Microbe In California's Largest Lake | work = ScienceDaily | date = 11 January 2005 | url = https://www.sciencedaily.com/releases/2005/01/050110112808.htm}}</ref> and mantis shrimp.
== In horticulture == Plants perceive light through internal photoreceptors absorbing a specified wavelength signaling (photomorphogenesis) or transferring the energy to a plant process (photosynthesis).<ref name="Sager et al.">{{cite journal |last1=Sager |first1=J.C. |last2=Smith |first2=W.O. |last3=Edwards |first3=J.L. |last4=Cyr |first4=K.L. |title=Photosynthetic efficiency and phytochrome photoequilibria determination using spectral data |journal=Transactions of the ASAE |date=1988 |volume=31 |issue=6 |pages=1882–1889|doi=10.13031/2013.30952 }}</ref> In plants, the photoreceptors cryptochrome and phototropin absorb radiation in the blue and UV/A regions of the spectrum (λ=340-500 nm) and regulate hypocotyl inhibition, flowering time, and phototropism<ref name="Lin">{{cite journal |last1=Lin |first1=Chentao |title=Plant blue-light receptors |journal=Trends in Plant Science |date=2000 |volume=5 |issue=8 |pages=337–42 |doi=10.1016/S1360-1385(00)01687-3 |pmid=10908878 |bibcode=2000TPS.....5..337L }}</ref>, whereas phytochrome photoreceptors absorb in the red (R: λ=630–700 nm) and far-red (FR: λ=700-750 nm) regions and influence many aspects of plant development such as germination, seedling etiolation, transition to flowering, shade avoidance, and tropisms.<ref name="Taiz and Zeiger">{{cite book |last1=Taiz |first1=Lincoln |last2=Zeiger |first2=Eduardo |title=Plant Physiology |date=2010 |publisher=Sinaur Associates, Inc. |location=Sunderland, Massachusetts |edition=5th}}</ref> Phytochrome has the ability to interchange its conformation based on the quantity or quality of light it perceives and does so via photoconversion from phytochrome red (Pr) to phytochrome far-red (Pfr).<ref>{{cite journal |last1=Heyes |first1=Derren |last2=Khara |first2=Basile |last3=Sakuma |first3=Michiyo |last4=Hardman |first4=Samantha |last5=O'Cualain |first5=Ronan |last6=Rigby |first6=Stephen |last7=Scrutton |first7=Nigel |title=Ultrafast red light activation of Synechocystis phytochrome Cph1 triggers major structural change to for the Pfr signaling-competent state |journal=PLOS ONE |date=2012 |volume=7 |issue=12 |article-number=e52418|doi=10.1371/journal.pone.0052418 |pmid=23300666 |pmc=3530517 |bibcode=2012PLoSO...752418H |doi-access=free }}</ref> Pr is the inactive form of phytochrome, ready to perceive red light. In a high R:FR environment, Pr changes conformation to the active form of phytochrome Pfr. Once active, Pfr translocates to the cellular nucleus, binds to phytochrome interacting factors (PIF), and targets the PIFs to the proteasome for degradation. Exposed to a low R:FR environment, Pfr absorbs FR and changes conformation back to the inactive Pr. The inactive conformation will remain in the cytosol, allowing PIFs to target their binding site on the genome and induce expression (i.e. shade avoidance through cellular elongation).<ref>{{cite journal |last1=Frankhauser |first1=Christian |title=The phytochroms, a family of red/far-red absorbing photoreceptors |journal=The Journal of Biological Chemistry |date=2001 |volume=276 |issue=15 |pages=11453–6 |doi=10.1074/jbc.R100006200 |pmid=11279228 |doi-access=free }}</ref> FR irradiation can lead to compromised plant immunity and increased pathogen susceptibility.<ref>{{cite journal |last1=Courbier |first1=Sarah |last2=Grevink |first2=Sanne |last3=Sluijs |first3=Emma |last4=Bonhomme |first4=Pierre-Olivier |last5=Kajala |first5=Kaisa |last6=Van Wees |first6=Saskia C.M. |last7=Pierik |first7=Ronald |title=Far-red light promotes Botrytis cinerea disease development in tomato leaves via jasmonate-dependent modulation of soluble sugars |journal=Plant, Cell & Environment |date=24 August 2020 |volume=43 |issue=11 |pages=2769–2781 |doi=10.1111/pce.13870|pmid=32833234 |pmc=7693051 |bibcode=2020PCEnv..43.2769C |doi-access=free }}</ref>
FR has long been considered a minimal input in photosynthesis. In the early 1970s, physics PhD and soil crop professor Keith J. McCree lobbied for a standard definition of photosynthetically active radiation (PAR: λ=400–700 nm) which did not include FR.<ref>{{cite journal |last1=McCree |first1=Keith |title=The action spectrum, absorbance and quantum yield of photosynthesis in crop plants |journal=Agricultural Meteorology |date=1972 |volume=9 |pages=191–216|doi=10.1016/0002-1571(71)90022-7 }}</ref> More recently, scientists have provided evidence that a broader spectrum called photo-biologically active radiation (PBAR: λ=280–800 nm) is more applicable terminology.<ref>{{cite journal |last1=Dӧrr |first1=Oliver |last2=Zimmermann |first2=Benno |last3=Kӧgler |first3=Stine |last4=Mibus |first4=Heiko |title=Influence of leaf temperature and blue light on the accumulation of rosmarinic acid and other phenolic compounds in Plectranthus scutellarioides (L.) |journal=Environmental and Experimental Botany |date=2019 |volume=167 |article-number=103830|doi=10.1016/j.envexpbot.2019.103830 |bibcode=2019EnvEB.16703830D |s2cid=201211911 }}</ref> This range of wavelengths not only includes FR, but also UV-A and UV-B. The Emerson effect established that the rate of photosynthesis in red and green algae was higher when exposed to R and FR than the sum of the two individually.<ref>{{cite journal |last1=Emerson |first1=Robert |last2=Chalmers |first2=Ruth |last3=Cederstrand |first3=Carl |title=Some factors influencing the long-wave limit of photosynthesis |journal= Proceedings of the National Academy of Sciences|date=1957 |volume=43 |issue=1 |pages=133–143 |doi=10.1073/pnas.43.1.133 |pmid=16589986 |pmc=528397 |bibcode=1957PNAS...43..133E |doi-access=free }}</ref> This research laid the ground work for the elucidation of the dual photosystems in plants. Photosystem I (PSI) and photosystem II (PSII) work synergistically; through photochemical processes PSII transports electrons to PSI. Any imbalance between R and FR leads to unequal excitation between PSI and PSII, thereby reducing the efficiency of photochemistry.<ref>{{cite journal |last1=Zhen |first1=S. |last2=van Iersel |first2=Marc W. |title=Far-red light is needed for efficient photochemistry and photosynthesis |journal=Journal of Plant Physiology |date=2017 |volume=209 |pages=115–122 |doi=10.1016/j.jplph.2016.12.004 |pmid=28039776 |bibcode=2017JPPhy.209..115Z |doi-access=free }}</ref><ref>{{cite web |last1=Pocock |first1=Tessa |title=The McCree curve demystified |url=https://www.potonics.com/a63340/The_McCree_Curve_Demystified |website=Biophotonics |access-date=10 October 2019 }}{{Dead link|date=July 2025 |bot=InternetArchiveBot |fix-attempted=yes }}</ref>
== See also == * Crown shyness
==References== === Citations === {{Reflist}}
=== General sources === * {{Cite journal |author=Fei Gan, Shuyi Zhang, Nathan C. Rockwell, Shelley S. Martin, J. Clark Lagarias, Donald A. Bryant |title=Extensive remodeling of a cyanobacterial photosynthetic apparatus in far-red light |journal=Science |date=12 September 2014 |volume=345 |issue=6202 |pages=1312–1317 |doi=10.1126/science.1256963|pmid=25214622 |bibcode=2014Sci...345.1312G |s2cid=206559762 |url=https://scholarworks.montana.edu/xmlui/handle/1/8715 |doi-access=free }}
{{color topics}}
Category:Color Category:Optical spectrum