Far-red light is a range of light at the extreme red end of the visible spectrum, just before infra-red 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.[1][2] Far-red light also is used for vision by certain organisms such as some species of deep-sea fishes[3][4] and mantis shrimp.

The visible spectrum; far-red is located at the far right.

In horticultureEdit

Plants perceive light through internal photoreceptors absorbing a specified wavelength signaling (photomorphogenesis) or transferring the energy to a plant process (photosynthesis).[5] In plants, the photoreceptors cryptochrome and phototropin absorb radiation in the blue spectrum (B: λ=400–500 nm) and regulate internal signaling such as hypocotyl inhibition, flowering time, and phototropism.[6] Additional receptors called phytochrome absorb radiation in the red (R: λ=660–730 nm) and far-red (FR: λ>730 nm) spectra and influence many aspects of plant development such as germination, seedling etiolation, transition to flowering, shade avoidance, and tropisms.[7] 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).[8] Pr is the inactive form of phytrochrome, 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).[9] FR irradiation can lead to compromised plant immunity and increased pathogen susceptibility. [10]

FR has long been considered a minimal input in photosynthesis. In the early 1970’s, PhD physicist and soil crop professor Dr. Keith J. McCree lobbied for a standard definition of photosynthetically active radiation (PAR: λ=400–700 nm) which did not include FR.[11] More recently, scientists have provided evidence that a broader spectrum called photo-biologically active radiation (PBAR: λ=280–800 nm) is more applicable terminology.[12] 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.[13] 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.[14][15]

See alsoEdit



  1. ^ Pettai, Hugo; Oja, Vello; Freiberg, Arvi; Laisk, Agu (2005). "Photosynthetic activity of far-red light in green plants". Biochimica et Biophysica Acta (BBA) - Bioenergetics. 1708 (3): 311–21. doi:10.1016/j.bbabio.2005.05.005. PMID 15950173.
  2. ^ Oquist, Gunnar (1969). "Adaptations in Pigment Composition and Photosynthesis by Far Red Radiation in Chlorella pyrenoidosa". Physiologia Plantarum. 22 (3): 516–528. doi:10.1111/j.1399-3054.1969.tb07406.x.
  3. ^ Douglas, R. H.; Partridge, J. C.; Dulai, K.; Hunt, D.; Mullineaux, C. W.; Tauber, A. Y.; Hynninen, P. H. (1998). "Dragon fish see using chlorophyll". Nature. 393 (6684): 423. Bibcode:1998Natur.393..423D. doi:10.1038/30871. S2CID 4416089.
  4. ^ "Scientists Discover Unique Microbe In California's Largest Lake". ScienceDaily. 11 January 2005.
  5. ^ Sager, J.C.; Smith, W.O.; Edwards, J.L.; Cyr, K.L. (1988). "Photosynthetic efficiency and phytochrome photoequilibria determination using spectral data". Transactions of the ASAE. 31 (6): 1882–1889. doi:10.13031/2013.30952.
  6. ^ Lin, Chentao (2000). "Plant blue-light receptors". Trends in Plant Science. 5 (8): 337–42. doi:10.1016/S1360-1385(00)01687-3. PMID 10908878.
  7. ^ Taiz, Lincoln; Zeiger, Eduardo (2010). Plant Physiology (5th ed.). Sunderland, Massachusetts: Sinaur Associates, Inc.
  8. ^ Heyes, Derren; Khara, Basile; Sakuma, Michiyo; Hardman, Samantha; O'Cualain, Ronan; Rigby, Stephen; Scrutton, Nigel (2012). "Ultrafast red light activation of Synechocystis phytochrome Cph1 triggers major structural change to for the Pfr signaling-competent state". PLOS ONE. 7 (12): e52418. Bibcode:2012PLoSO...752418H. doi:10.1371/journal.pone.0052418. PMC 3530517. PMID 23300666.
  9. ^ Frankhauser, Christian (2001). "The phytochroms, a family of red/far-red absorbing photoreceptors". The Journal of Biological Chemistry. 276 (15): 11453–6. doi:10.1074/jbc.R100006200. PMID 11279228.
  10. ^ Courbier, Sarah; Grevink, Sanne; Sluijs, Emma; Bonhomme, Pierre‐Olivier; Kajala, Kaisa; Van Wees, Saskia C.M.; Pierik, Ronald (24 August 2020). "Far‐red light promotes Botrytis cinerea disease development in tomato leaves via jasmonate‐dependent modulation of soluble sugars". Plant, Cell & Environment. 43 (11): 2769–2781. doi:10.1111/pce.13870. PMC 7693051. PMID 32833234.
  11. ^ McCree, Keith (1972). "The action spectrum, absorbance and quantum yield of photosynthesis in crop plants". Agricultural Meteorology. 9: 191–216. doi:10.1016/0002-1571(71)90022-7.
  12. ^ Dӧrr, Oliver; Zimmermann, Benno; Kӧgler, Stine; Mibus, Heiko (2019). "Influence of leaf temperature and blue light on the accumulation of rosmarinic acid and other phenolic compounds in Plectranthus scutellarioides (L.)". Environmental and Experimental Botany. 167: 103830. doi:10.1016/j.envexpbot.2019.103830.
  13. ^ Emerson, Robert; Chalmers, Ruth; Cederstrand, Carl (1957). "Some factors influencing the long-wave limit of photosynthesis". Proceedings of the National Academy of Sciences. 43 (1): 133–143. Bibcode:1957PNAS...43..133E. doi:10.1073/pnas.43.1.133. PMC 528397. PMID 16589986.
  14. ^ Zhen, S.; van Iersel, Marc W. (2017). "Far-red light is needed for efficient photochemistry and photosynthesis". Journal of Plant Physiology. 209: 115–122. doi:10.1016/j.jplph.2016.12.004. PMID 28039776.
  15. ^ Pocock, Tessa. "The McCree curve demystified". Biophotonics. Retrieved 10 October 2019.

General sourcesEdit