Vernalization
Encyclopedia
Vernalization is the acquisition of a plant
's ability to flower
or germinate
in the spring by exposure to the prolonged cold of winter. 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.
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. 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 to break dormancy, prior to flowering. Many monocarpic
annuals
and biennials
, including some ecotype
s of Arabidopsis thaliana
and winter cereals such as wheat
, must go through a prolonged period of cold before flowering occurs.
, farmers observed a traditional distinction between "winter cereals," whose seeds require chilling, and "spring cereals," whose seeds can be sown in spring and flower soon thereafter. The word "vernalization" is a translation of "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). 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.
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. 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.
Early research on vernalization focused on plant physiology; the increasing availability of molecular biology has made it possible to unravel its underlying mechanisms. For example, 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).
Due to plant flowering requiring the successful co-operation of several metabolic pathway
s, computer models that incorporate vernalization have also been made.
of its five chromosomes was completely sequenced. Some variants, called "winter annuals", require vernalization to flower; others ("summer annuals") do not. The genes that underlie this difference in plant physiology have been intensively studied.
The reproductive phase change of A. thalliana occurs by a sequence of two related events: first, the bolting transition (flower stalk elongates), then the floral transition (first flower appears). Bolting is a robust predictor of flower formation, and hence a good indicator for vernalization research.
In arabidopsis winter annuals, the apical meristem is the part of the plant that needs to be chilled. 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.
Before vernalization, flowering is repressed by the action of a gene called Flowering Locus Controller (FLC). Vernalization activates a gene called Frigida (FRI), which progressively turns off FLC expression over a period of six weeks. Since vernalization also occurs in flc mutants (lacking FLC), vernalization must also activate a non-FLC pathway. A day-length mechanism is also important.
Plant
Plants are living organisms belonging to the kingdom Plantae. Precise definitions of the kingdom vary, but as the term is used here, plants include familiar organisms such as trees, flowers, herbs, bushes, grasses, vines, ferns, mosses, and green algae. The group is also called green plants or...
's ability to flower
Flower
A flower, sometimes known as a bloom or blossom, is the reproductive structure found in flowering plants . The biological function of a flower is to effect reproduction, usually by providing a mechanism for the union of sperm with eggs...
or germinate
Germination
Germination is the process in which a plant or fungus emerges from a seed or spore, respectively, and begins growth. The most common example of germination is the sprouting of a seedling from a seed of an angiosperm or gymnosperm. However the growth of a sporeling from a spore, for example the...
in the spring by exposure to the prolonged cold of winter. 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.
Many plants grown in temperate
Temperate
In geography, temperate or tepid latitudes of the globe lie between the tropics and the polar circles. The changes in these regions between summer and winter are generally relatively moderate, rather than extreme hot or cold...
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. The needed cold is often expressed in chill hours
Chilling requirement
The chilling requirement of a fruit is the minimum period of cold weather after which a fruit-bearing tree will blossom. It is often expressed in chill hours, which can be calculated in different ways, all of which essentially involve adding up the total amount of time in a winter spent at certain...
. Typical vernalization temperatures are between 5 and 10 degrees Celsius (40 and 50 degrees Fahrenheit).
For many perennial plants, such as fruit tree
Fruit tree
A fruit tree is a tree which bears fruit that is consumed or used by people — all trees that are flowering plants produce fruit, which are the ripened ovaries of flowers containing one or more seeds. In horticultural usage, the term 'fruit tree' is limited to those that provide fruit for...
species, a period of cold is needed to break dormancy, prior to flowering. Many monocarpic
Monocarpic
Monocarpic plants are those that flower, set seeds and then die. Other terms with the same meaning are hapaxanth and semelparous. The term was first used by Alphonse de Candolle....
annuals
Annual plant
An annual plant is a plant that usually germinates, flowers, and dies in a year or season. True annuals will only live longer than a year if they are prevented from setting seed...
and biennials
Biennial plant
A biennial plant is a flowering plant that takes two years to complete its biological lifecycle. In the first year the plant grows leaves, stems, and roots , then it enters a period of dormancy over the colder months. Usually the stem remains very short and the leaves are low to the ground, forming...
, including some ecotype
Ecotype
In evolutionary ecology, an ecotype,Greek: οίκος = home and τύπος = type, coined by Göte Turesson in 1922 sometimes called ecospecies, describes a genetically distinct geographic variety, population or race within species , which is adapted to specific environmental conditions.Typically, ecotypes...
s of Arabidopsis thaliana
Arabidopsis thaliana
Arabidopsis thaliana is a small flowering plant native to Europe, Asia, and northwestern Africa. A spring annual with a relatively short life cycle, arabidopsis is popular as a model organism in plant biology and genetics...
and winter cereals such as wheat
Wheat
Wheat is a cereal grain, originally from the Levant region of the Near East, but now cultivated worldwide. In 2007 world production of wheat was 607 million tons, making it the third most-produced cereal after maize and rice...
, must go through a prolonged period of cold before flowering occurs.
History of vernalization research
In the history of agricultureHistory of agriculture
Agriculture was developed at least 10,000 years ago, and it has undergone significant developments since the time of the earliest cultivation. The Fertile Crescent of Western Asia, Egypt, and India were sites of the earliest planned sowing and harvesting of plants that had previously been gathered...
, farmers observed a traditional distinction between "winter cereals," whose seeds require chilling, and "spring cereals," whose seeds can be sown in spring and flower soon thereafter. The word "vernalization" is a translation of "Jarovization," a word coined by Trofim Lysenko
Trofim Lysenko
Trofim Denisovich Lysenko was a Soviet agronomist of Ukrainian origin, who was director of Soviet biology under Joseph Stalin. Lysenko rejected Mendelian genetics in favor of the hybridization theories of Russian horticulturist Ivan Vladimirovich Michurin, and adopted them into a powerful...
to describe a chilling process he used to make the seeds of winter cereals behave like spring cereals ("Jarovoe" in Russian). 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.
Lysenko's 1928 paper on vernalization and plant physiology
Plant physiology
Plant physiology is a subdiscipline of botany concerned with the functioning, or physiology, of plants. Closely related fields include plant morphology , plant ecology , phytochemistry , cell biology, and molecular biology.Fundamental processes such as photosynthesis, respiration, plant nutrition,...
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. 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.
Early research on vernalization focused on plant physiology; the increasing availability of molecular biology has made it possible to unravel its underlying mechanisms. For example, 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).
Due to plant flowering requiring the successful co-operation of several metabolic pathway
Metabolic pathway
In biochemistry, metabolic pathways are series of chemical reactions occurring within a cell. In each pathway, a principal chemical is modified by a series of chemical reactions. Enzymes catalyze these reactions, and often require dietary minerals, vitamins, and other cofactors in order to function...
s, computer models that incorporate vernalization have also been made.
Vernalization in Arabidopsis thaliana
Arabidopsis thaliana, also known as "thale cress," is a much-studied model species. In 2000, the entire genomeGenome
In modern molecular biology and genetics, the genome is the entirety of an organism's hereditary information. It is encoded either in DNA or, for many types of virus, in RNA. The genome includes both the genes and the non-coding sequences of the DNA/RNA....
of its five chromosomes was completely sequenced. Some variants, called "winter annuals", require vernalization to flower; others ("summer annuals") do not. The genes that underlie this difference in plant physiology have been intensively studied.
The reproductive phase change of A. thalliana occurs by a sequence of two related events: first, the bolting transition (flower stalk elongates), then the floral transition (first flower appears). Bolting is a robust predictor of flower formation, and hence a good indicator for vernalization research.
In arabidopsis winter annuals, the apical meristem is the part of the plant that needs to be chilled. Vernalization of the meristem
Meristem
A meristem is the tissue in most plants consisting of undifferentiated cells , found in zones of the plant where growth can take place....
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.
Before vernalization, flowering is repressed by the action of a gene called Flowering Locus Controller (FLC). Vernalization activates a gene called Frigida (FRI), which progressively turns off FLC expression over a period of six weeks. Since vernalization also occurs in flc mutants (lacking FLC), vernalization must also activate a non-FLC pathway. A day-length mechanism is also important.