Vernalization

Process of Vernalization

Vernalization is derived from the Latin word “vernus”, meaning “of spring”. It is the process of inducing flowering in a plant by exposing it to extended periods of cold temperatures or similar conditions. Once this process has occurred, the plant will become capable of flowering, though it may require additional weeks of growth before it actually blooms.

In the process of vernalization, a cold treatment is provided to a completely hydrated seed or a growing plant, which facilitates flowering. This process restricts the vegetative phase of the plant, resulting in early flowering. Without the cold treatment, plants requiring vernalization will either flower later or remain in the vegetative phase.

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Types of Vernalization

Vernalization can be of the following types:

Obligate Vernalization

Plants must be exposed to lower temperatures for a specified period of time. Example – Biennial plants (cabbage)

Facultative Vernalization

Flowering in plants appears earlier when exposed to lower temperatures. For example, winter annual triticale.

Mechanism of Vernalization

Two main hypotheses have been proposed to explain the mechanism of vernalization:

  1. Advancement in the process of blooming due to a delayed period of low temperatures, such as those experienced in winter
  2. Other hypotheses that have yet to be identified

Phasic Development Theory

Hormonal Theories

Phasic Development Theory

As per this hypothesis, there is an organization of stages in the plant’s improvement. These stages are impacted by environmental elements such as light, temperature, etc. There are two main stages in this process:

Thermostage is the vegetative phase that depends on temperature, wherein vernalization accelerates the thermostat. It requires low heat, aeration, and enough dampness.

Vernalin assists in producing florigen, which is necessary for Photostage to function at a high temperature.

Hormonal Theories

The hypothesis states that freezing treatment can cause the development of a hormone called vernalin, which is then dispersed to different parts of the plant. This hormone, vernalin, is then able to diffuse from vernalized plants to unvernalized plants, leading to flowering.

Vernalization in Plants: Site of Vernalization

The metabolically active apical meristems are the sites of perception of temperature to initiate flowering. The younger leaves are more susceptible to the process of vernalization. The shoot apex of mature stems or embryo of seeds receives low temperature stimulus. Consequently, the stimulus of this process is perceived by meristematic cells only such as the shoot tips, root apex, developing leaves, embryo tips, etc.

Vernalization Examples:

  • Wheat
  • Barley
  • Oats
  • Rye

Some food plants have a spring or winter variety, wherein the spring variety is typically planted in the spring. Hence, flowers produce grains towards the end of this season. However, the winter variety is planted in autumn wherein it germinates in winter, grows in the spring and is harvested the following summer. Biennial plants require two years for flowering as they grow stem, leaves and roots in the first year and for the cold months enter into dormancy. In the subsequent months, it requires a period of cold or vernalization for the process of flowering. Gradually, biennial plants flower producing fruits and in the following summer/spring, they die. Some examples are cabbages, carrots, and sugarbeets.

Predominantly, garlic is planted during winter, as it requires cold temperatures (vernalization). If the temperature is not low enough for a sufficient amount of time, garlic will not form bulbs, and winter wheat will not flower and produce grain in the following season.

Devernalization

Devernalization is the reversal of the process of vernalization due to exposure to higher temperatures. This process can be affected by treating vernalized buds or seeds with a high range of temperature. In 1957, Lang et al. demonstrated that applying gibberellins can substitute the cold treatment for vernalization in some biennial plants.

Factors Affecting Vernalization

The following factors affect the process of vernalization:

Age of the Plants

Site of Vernalization

Provision of suitable low temperature

Oxygen

Duration of Exposure

Water

Also See:

What Are The Requirements For Vernalization?

Where Does Vernalization Take Place?

Significance of Vernalization

This process can help to reduce the length of the vegetative phase of a plant and facilitate early flowering, which is suitable for temperate and some tropical plants.

Through vernalization, Kernel wrinkles of Triticale can be eliminated.

It increases the yield and resistance of plants to fungal diseases.

It enhances the cold tolerance of plants

Aids in the improvement of crops

Vernalization in biennials can induce early flowering and early fruit setting

Grafting, which is used in horticulture, can induce the process of flowering.

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