What is Vernalization?
Temperature plays a crucial role in seed germination and flowering. Germination of plants at temperate zone occurs at low temperature on the other hand plants of tropical zone require much high temperature for germination.
Artificial change in temperature can control the germination of many temperate plants. Lysenko the Soviet agronomist observed that pre-treatment of winter strains wheat seeds to chilling temperature leads them to be planted in spring this phenomenon was further explained by Chourad a French botanist, as “as the acquisition of acceleration of the ability to flower by chilling treatment.
Vernalization is the process that induces early flowering in plants by exposing them to low temperatures”.
Pre-treatment of freezing temperature to seeds inhibits its reproductive development in autumn which enables plants to attain vegetative maturity before the initiation of reproduction eg. Wheat, rye, sugarbeet, chrysanthemum.
Location of Vernalization
In mature plants, stem apex or meristematic cell is the main site to receive stimulus but in some specices all dividing cells of leaves and roots can act as a signal receptor for vernalization in different plants.
Conditions for Vernalization
1. Low temperature: Vernalization is a gradual process, it takes nearly 45 to 50 days of treatment between 1 degree to six degree celcius.
2. Meristematic cells: Vernalization only occurs in actively dividing cells, it requires an active embryo, to fulfill these demands seeds are moistened before treating them with low temperature.
3. Proper nourishment
4. Water: sufficient amount of water is essentially required for the effect.
5. Aerobic respiration: metabolic energy is required for vernalization and the treatment becomes ineffective in the absence of oxygen.
Etiology of Vernalization
There are two theories to define vernalization;
1. Phasic development theory
2. Hormonal theory
1. Phasic development theory: Lysenko in 1934 proposed that environmental factors (light, temperature) affects the different developing phases of plants.
He described that plants mainly follow two phases thermophase and photophase. Thermophases are regulated by temperature and vernalization speeds up this phase.
This phase is followed by a light-regulated factor called photophase.
2. Hormonal theory: In 1939 Melchar proposed that cold treatment to seeds initiate the synthesis of a new floral hormone called “vernalin”.
In an experiment, Melchar induced flowering in un-vernalized plants by grafting it with vernalized plants, this activity is explained by the fact that hormone vernalin diffuses from vernalized plant to the un-vernalized plant and results in flowering.
In 1957 lang et al revealed that for vernalization exposure of gibberellin can be used instead of cold treatment.
Role of Epigenetic Changes in Vernalization
Some studies on LDP Arabidopsis showed that epigenetic changes played important role in the regulation of vernalization.
It has been suggested that a repressor gene Flowering LOCUS C (FLC) is found overexpressed in non vernalized shoot apical meristem, this gene deactivates epigenetically after vernalization.
Difference Between Photoperiodism and Vernalization
In photoperiodism flowering of the plant takes place following the preparation process, but vernalization only prepares plants to flower, the initiation of only happens in the presence of suitable conditions.
Application of Vernalization
• Vernalization reduces the vegetative period of plants and induces early flowering in both temperate and tropical plants for eg. Rice, wheat, cotton.
• Vernalization can remove Kernal wrinkles in the Triticale.
• Vernalization brings cold and diseases resistance in plants which subsequently increases the yield.