Vernalization

Many species of henbane require vernalization before flowering.

Vernalization (from Latin vernus, "of the spring") is the induction of a plant's flowering process by exposure to the prolonged cold of winter, or by an artificial equivalent. After vernalization, plants have acquired the ability to flower, but they may require additional seasonal cues or weeks of growth before they will actually flower. Vernalization is sometimes used to refer to herbal (non-woody) plants requiring a cold dormancy to produce new shoots and leaves[1] but this usage is discouraged [2]

Many plants grown in temperate climates require vernalization and must experience a period of low winter temperature to initiate or accelerate the flowering process. This ensures that reproductive development and seed production occurs in spring and summer, rather than in autumn.[3] The needed cold is often expressed in chill hours. Typical vernalization temperatures are between 5 and 10 degrees Celsius (40 and 50 degrees Fahrenheit).

For many perennial plants, such as fruit tree species, a period of cold is needed first to induce dormancy and then later, after the requisite period of time, re-emerge from that dormancy prior to flowering. Many monocarpic winter annuals and biennials, including some ecotypes of Arabidopsis thaliana[4] and winter cereals such as wheat, must go through a prolonged period of cold before flowering occurs.

History of vernalization research

In the history of agriculture, farmers observed a traditional distinction between "winter cereals," whose seeds require chilling (to trigger their subsequent emergence and growth), and "spring cereals," whose seeds can be sown in spring, and germinate, and then flower soon thereafter.[2] The word "vernalization" is a translation of "яровизация" ("jarovization") a word coined by Trofim Lysenko to describe a chilling process he used to make the seeds of winter cereals behave like spring cereals ("Jarovoe" in Russian).[2] Scientists had also discussed how some plants needed cold temperatures to flower, as early as the 18th century, with the German plant physiologist Gustav Gassner often mentioned for his 1918 paper.[2][5]

Lysenko's 1928 paper on vernalization and plant physiology drew wide attention due to its practical consequences for Russian agriculture. Severe cold and lack of winter snow had destroyed many early winter wheat seedlings. By treating wheat seeds with moisture as well as cold, Lysenko induced them to bear a crop when planted in spring.[5] Later however, Lysenko inaccurately asserted that the vernalized state could be inherited - i.e., that the offspring of a vernalized plant would behave as if they themselves had also been vernalized and would not require vernalization in order to flower quickly.[6]

Early research on vernalization focused on plant physiology; the increasing availability of molecular biology has made it possible to unravel its underlying mechanisms.[6] For example, a lengthening daylight period (longer days), as well as cold temperatures are required for winter wheat plants to go from the vegetative to the reproductive state; the three interacting genes are called VRN1, VRN2, and FT (VRN3).[7]

Due to plant flowering requiring the successful co-operation of several metabolic pathways, computer models that incorporate vernalization have also been made.[8]

In Arabidopsis thaliana

Arabidopsis thaliana rosette before vernalization, with no floral spike

Arabidopsis thaliana ("thale cress") is a much-studied model for vernalization. Some ecotypes (varieties), called "winter annuals", have delayed flowering without vernalization; others ("summer annuals") do not.[9] The genes that underlie this difference in plant physiology have been intensively studied.[6]

The reproductive phase change of A. thaliana occurs by a sequence of two related events: first, the bolting transition (flower stalk elongates), then the floral transition (first flower appears).[10] Bolting is a robust predictor of flower formation, and hence a good indicator for vernalization research.[10]

In winter annual Arabidopsis, vernalization of the meristem appears to confer competence to respond to floral inductive signals. A vernalized meristem retains competence for as long as 300 days in the absence of an inductive signal.[9]

At the molecular level, flowering is repressed by the protein Flowering Locus C (FLC), which binds to and represses genes that promote flowering, thus blocking flowering.[3][11] Winter annual ecotypes of Arabidopsis have an active copy of the gene FRIGIDA (FRI), which promotes FLC expression, thus repression of flowering.[12] Prolonged exposure to cold (vernalization) induces expression of VERNALIZATION INSENSTIVE3, which interacts with the VERNALIZATION2 polycomb-like complex to reduce FLC expression through chromatin remodeling.[13] The epigenetic silencing of FLC by chromatin remodeling is also thought to involve the cold-induced expression of antisense FLC COOLAIR[14][15] or COLDAIR transcripts.[16] Vernalization is registered by the plant by the stable silencing of individual FLC loci.[17] The removal of silent chromatin marks at FLC during embryogenesis prevents the inheritance of the vernalized state [18]

Since vernalization also occurs in flc mutants (lacking FLC), vernalization must also activate a non-FLC pathway.[19] A day-length mechanism is also important.[7]

Devernalization

It is possible to devernalize a plant by exposure to high temperatures subsequent to vernalization. For example, commercial onion growers store sets at low temperatures, but devernalize them before planting, because they want the plant's energy to go into enlarging its bulb (underground stem), not making flowers.[20]

References

  1. ↑ Sokolski, K.; Dovholuk, A.; Dovholuk, L.; Faletra, P. (1997). "Axenic seed culture and micropropagation of Cypripedium reginae". Selbyana 18 (2): 172–82. JSTOR 41760430.
  2. 1 2 3 4 Chouard, P. (June 1960). "Vernalization and its relations to dormancy". Annual Review of Plant Physiology (Annual Reviews) 11: 191–238. doi:10.1146/annurev.pp.11.060160.001203.
  3. 1 2 Sung, Sibum; He, Yuehui; Eshoo, Tifani W; Tamada, Yosuke; Johnson, Lianna; Nakahigashi, Kenji; Goto, Koji; Jacobsen, Steve E; Amasino, Richard M (2006). "Epigenetic maintenance of the vernalized state in Arabidopsis thaliana requires LIKE HETEROCHROMATIN PROTEIN 1". Nature Genetics 38 (6): 706–10. doi:10.1038/ng1795. PMID 16682972.
  4. ↑ Michaels, Scott D.; He, Yuehui; Scortecci, Katia C.; Amasino, Richard M. (2003). "Attenuation of FLOWERING LOCUS C activity as a mechanism for the evolution of summer-annual flowering behavior in Arabidopsis". Proceedings of the National Academy of Sciences 100 (17): 10102–7. Bibcode:2003PNAS..10010102M. doi:10.1073/pnas.1531467100. JSTOR 3147669. PMC 187779. PMID 12904584.
  5. 1 2 Roll-Hansen, Nils (1985). "A new perspective on Lysenko?". Annals of Science (Taylor & Francis) 42 (3): 261–278. doi:10.1080/00033798500200201. PMID 11620694.
  6. 1 2 3 Richard Amasino (October 2004). "Vernalization, Competence, and the Epigenetic Memory of Winter". Plant Cell (American Society of Plant Biologists) 16 (10): 2553–2559. doi:10.1105/tpc.104.161070. PMC 520954. PMID 15466409.
  7. 1 2 Trevaskis, Ben; Hemming, Megan N.; Dennis, Elizabeth S. (August 2007). "The molecular basis of vernalization-induced flowering in cereals". Trends in Plant Science (Elsevier) 12 (8): 352–357. doi:10.1016/j.tplants.2007.06.010. PMID 17629542.
  8. ↑ "New Genetic Model Predicts Plant Flowering in Different Environments" (Press release). Brown University. January 15, 2009. Retrieved March 20, 2016.
  9. 1 2 "Vernalisation response". Plant Biology. Retrieved 2011-01-26.
  10. 1 2 Pouteau, Sylvie; Albertini, Catherine (2009). "The significance of bolting and floral transitions as indicators of reproductive phase change in Arabidopsis". Journal of Experimental Botany 60 (12): 3367–77. doi:10.1093/jxb/erp173. PMID 19502535.
  11. ↑ Amasino, Richard (2010). "Seasonal and developmental timing of flowering". The Plant Journal 61 (6): 1001–13. doi:10.1111/j.1365-313X.2010.04148.x. PMID 20409274.
  12. ↑ Choi, Kyuha; Kim, Juhyun; Hwang, Hyun-Ju; Kim, Sanghee; Park, Chulmin; Kim, Sang Yeol; Lee, Ilha (2011). "The FRIGIDA Complex Activates Transcription ofFLC, a Strong Flowering Repressor inArabidopsis, by Recruiting Chromatin Modification Factors". The Plant Cell 23 (1): 289–303. doi:10.1105/tpc.110.075911. PMC 3051252. PMID 21282526.
  13. ↑ Sung, Sibum; Amasino, Richard M. (2004). "Vernalization in Arabidopsis thaliana is mediated by the PHD finger protein VIN3". Nature 427 (6970): 159–163. Bibcode:2004Natur.427..159S. doi:10.1038/nature02195.
  14. ↑ http://www.jic.ac.uk/news/2014/10/plants-require-coolair-flower-spring[]
  15. ↑ Csorba, Tibor; Questa, Julia I.; Sun, Qianwen; Dean, Caroline (2014). "Antisense COOLAIR mediates the coordinated switching of chromatin states atFLCduring vernalization". Proceedings of the National Academy of Sciences 111 (45): 16160–5. Bibcode:2014PNAS..11116160C. doi:10.1073/pnas.1419030111. PMC 4234544. PMID 25349421.
  16. ↑ Heo, J. B.; Sung, S. (2011). "Vernalization-Mediated Epigenetic Silencing by a Long Intronic Noncoding RNA". Science 331 (6013): 76–9. doi:10.1126/science.1197349. PMID 21127216.
  17. ↑ Angel, Andrew; Song, Jie; Dean, Caroline; Howard, Martin (2011). "A Polycomb-based switch underlying quantitative epigenetic memory". Nature 476 (7358): 105–8. doi:10.1038/nature10241. PMID 21785438.
  18. ↑ Crevillén, Pedro; Yang, Hongchun; Cui, Xia; Greeff, Christiaan; Trick, Martin; Qiu, Qi; Cao, Xiaofeng; Dean, Caroline (2014). "Epigenetic reprogramming that prevents transgenerational inheritance of the vernalized state". Nature 515 (7528): 587–90. doi:10.1038/nature13722. PMC 4247276. PMID 25219852.
  19. ↑ "Vernalisation pathway". Plant Biology. Retrieved 2011-01-26.
  20. ↑ "Vernalization". Encyclopædia Britannica Online. Retrieved 2011-01-24. vernalization, the artificial exposure of plants (or seeds) to low temperatures in order to stimulate flowering or to enhance seed production. By satisfying the cold requirement of many temperate-zone plants, flowering can be induced to occur earlier than normal or in warm climates lacking the requisite seasonal chilling.

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