Vernalization
Vernalization (from
Many plants grown in
For many
History of vernalization research
In the
In 1928, the Soviet agronomist Trofim Lysenko published his works on the effects of cold on cereal seeds, and coined the term "яровизация" ("jarovization") to describe a chilling process he used to make the seeds of winter cereals behave like spring cereals (Jarovoe in Russian, originally from jar meaning fire or the god of spring). Lysenko himself translated the term into "vernalization" (from the Latin vernum meaning Spring). After Lysenko the term was used to explain the ability of flowering in some plants after a period of chilling due to physiological changes and external factors. The formal definition was given in 1960 by a French botanist P. Chouard, as "the acquisition or acceleration of the ability to flower by a chilling treatment".[7]
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.[8] Later however, according to Richard Amasino, Lysenko inaccurately asserted that the vernalized state could be inherited, i.e. 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.[9] Opposing this view and supporting Lysenko's claim, Xiuju Li and Yongsheng Liu have detailed experimental evidence from the USSR, Hungary, Bulgaria and China that shows the conversion between spring wheat and winter wheat, positing that "it is not unreasonable to postulate epigenetic mechanisms that could plausibly result in the conversion of spring to winter wheat or vice versa."[10]
Early research on vernalization focused on plant physiology; the increasing availability of molecular biology has made it possible to unravel its underlying mechanisms.[9] 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).[11]
In Arabidopsis thaliana
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.[12][self-published source?] The genes that underlie this difference in plant physiology have been intensively studied.[9]
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).[13] Bolting is a robust predictor of flower formation, and hence a good indicator for vernalization research.[13]
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.[12]
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][14] Winter annual ecotypes of Arabidopsis have an active copy of the gene FRIGIDA (FRI), which promotes FLC expression, thus repression of flowering.[15] Prolonged exposure to cold (vernalization) induces expression of VERNALIZATION INSENSTIVE3, which interacts with the VERNALIZATION2 (VRN2) polycomb-like complex to reduce FLC expression through chromatin remodeling.[16] Levels of VRN2 protein increase during long-term cold exposure as a result of inhibition of VRN2 turnover via its N-degron.[17] The events of histone deacetylation at Lysine 9 and 14 followed by methylation at Lys 9 and 27 is associated with the vernalization response. The epigenetic silencing of FLC by chromatin remodeling is also thought to involve the cold-induced expression of antisense FLC COOLAIR[18][19] or COLDAIR transcripts.[20] Vernalization is registered by the plant by the stable silencing of individual FLC loci.[21] The removal of silent chromatin marks at FLC during embryogenesis prevents the inheritance of the vernalized state.[22]
Since vernalization also occurs in flc mutants (lacking FLC), vernalization must also activate a non-FLC pathway.[23][self-published source?] A day-length mechanism is also important.[11] Vernalization response works in concert with the photo-periodic genes CO, FT, PHYA, CRY2 to induce flowering.
Devernalization
It is possible to devernalize a plant by exposure to sometimes low and 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.[24]
See also
References
- JSTOR 41760430.
- .
- ^ S2CID 2855447.
- ISBN 978-1-60535-255-8.
- PMID 12904584.
- .
- ISBN 978-0-08-100068-7.
- PMID 11620694.
- ^ PMID 15466409.
- S2CID 10527354.
- ^ PMID 17629542.
- ^ a b "Vernalisation response". Plant Biology. Retrieved 26 January 2011.[self-published source]
- ^ PMID 19502535.
- PMID 20409274.
- PMID 21282526.
- S2CID 4418494.
- PMID 30575749.
- ^ http://www.jic.ac.uk/news/2014/10/plants-require-coolair-flower-spring Archived 23 April 2015 at the Wayback Machine[full citation needed]
- PMID 25349421.
- S2CID 19127414.
- S2CID 205225603.
- PMID 25219852.
- ^ "Vernalisation pathway". Plant Biology. Retrieved 26 January 2011.[self-published source]
- ^
"Vernalization". Encyclopædia Britannica Online. Retrieved 3 September 2023.
Devernalization can be brought about by high temperatures ... Onion sets ... are ... ready to flower ... temperatures above 26.7 °C (80 °F) ..., however, shifts the sets to the desired bulb-forming phase.