Vernalization
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Vernalization (vernalisation - British English) is the acquisition of the competence to flower in the spring by exposure to the prolonged cold of winter. The word vernalization comes from the Latin word “vernus,’ meaning “of the spring.”
Many temperate plants have a vernalization requirement and must experience a period of low winter temperature to initiate or accelerate the flowering process, or, as the case with many fruit tree species, to actually break dormancy, prior to flowering.
One of the most important influences that temperature has on the floral transition is the vernalization response. Many plant species, including winter cereals such as wheat through to Arabidopsis thaliana, must go through a prolonged period of cold before flowering occurs. This ensures that reproductive development and seed production occurs at the optimum environmentally favorable time, normally following the passing of winter.
Following vernalization, plants have acquired the competence to flower, although they may require additional seasonal cues or weeks of growth before they will actually flower.
In the much studied model species Arabidopsis thaliana the apical meristem must be vernalized in order to promote flowering. Vernalization of the meristem appears to confer competence to respond to floral inductive signals on the meristem. A vernalized meristem retains competence for as long as 300 days in the absence of an inductive signal. It is possible to de-vernalize a plant by exposure to high temperatures subsequent to vernalization.
Some plant species do not flower without vernalization. Many biennial species have a vernalization period, which can vary in period and temperature. Typical vernalization temperatures are between 40 and 50 degrees Fahrenheit.
[edit] Molecular mechanisms of vernalization
The molecular mechanism of vernalization has been most extensively studied in the model plant Arabidopsis thaliana, although the process is not yet fully understood. In A. thaliana, flowering is prevented by high levels of the protein Flowering Locus C (FLC). During vernalization, FLC levels are reduced, allowing the plant to flower. The reduction of FLC is accompanied by the modification of the chromatin associated with the FLC gene. The reduction of FLC is in part mediated by the protein Vernalization Insenstive3 (VIN3), which appears only after the plant has been exposed to prolonged cold and which disappears following the cessation of cold. Following the return to warm conditions, the proteins Vernalization1 (VRN1) and Vernalization2 (VRN2) act to keep FLC at a low level.
Vernalization mechanisms may differ among plant species, meaning that what has been determined regarding vernalization in A. thaliana may not be applicable to other plant species. In winter wheat, for instance, vernalization is known to be controlled by a set of genes that are not evolutionarily related to the genes that control vernalization in A. thaliana.
[edit] Lysenkoism
During the Lysenkoist period in the Soviet Union, Trofim 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.
Many of the successes of the "new" agrotechnique employed on a number of agricultural species were either faked by Lysenkoites, or had their roots in extensive manual labor on experimental crops. For example, the vernalized potatoes were usually cut in parts to make more material to seed, cut sides were covered with charcoal to prevent the mold from growing, etc. The cost of human labor was nil, so the vernalized crops seemed more profitable to the state. Later Lysenko himself denounced his idea, carefully phrasing it that "vernalization in mass planning proved nonviable."
