Definition process types and differences between photoperiodism vernalisation and seed dormancy
Photoperiodism in Plants
As you all know that the plant growth regulators are simple organic molecules that play a vital role in the growth and development of the plants. Apart from these plant hormones or phytohormones, the plant growth is also influenced by certain external factors such as the temperature, the length of a day, light and dark exposures, etc.
From the observations of W. W. Garner and H. A. Allard, it was noticed that every plant does not require the same intensity of light and darkness for their flowering. Plants require only a specific phase of the light and the darkness for their flowering and this term is known to be the critical period. Based on these observations, they classified plants into three different categories which are:
Long Day Plants: The plants that require longer exposure to the light than their critical period. For eg: oats, and wheat
Short Day Plants: The plants that require a shorter period than their critical period. For eg: Chrysanthemum, and tobacco
Day-Neutral Plants: The plants in which the flowering is unaffected by the photoperiod. For eg. maize, and sunflower.
In this article, we will learn about photoperiodism, dormancy and vernalization in plants in detail. Let us first take a look at what is photoperiodism in plants.
Photoperiodism Definition
Photoperiodism refers to the phenomenon that is seen in most of the plants. It is the developmental responses of the plants wherein they are exposed either more towards the day or night for a specific length of day for inducing the flowering.
The continuation of the dark period is equally important. Hence, it can be said that in several plants, the flowering depends on the duration of the light and the darkness exposures. This specific response to the light and dark is known as photoperiodism.
Importance of Photoperiodism in Plants
The plants that require more exposure to the light are known as the long-day plants while those that require less exposure to the light are known as short-day plants. The length of day or night depends on plants to plants.
Examples of the long-day plants are irises, lettuce, radishes, spinach, etc. Christmas cactus and poinsettias chrysanthemums are a few examples of the short-day plants.
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Vernalization Process
The term vernalization is used to describe the dependence of specific plants on exposure to low temperature for the flowering qualitatively or quantitatively. It inhibits the development of the reproductive organs during the growing season and permits the plant to have adequate time for reaching its maturity stage.
Importance of Vernalization
Vernalization is the phenomenon that is practised for the production of the earlier crops. They are usually cultivated in the places wherein they naturally do not grow. Vernalization helps in the acceleration of the plant breeding.
For example: the wheat plants that have two varieties, winter and spring. Beet, cabbage, turnips and onions are examples of vernalization.
The winter variety is planted in the autumn season. They get time for germination and come out as small seedlings in the winter, then continue to grow in the spring and are harvested in the mid-summer.
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Seed Dormancy Definition
Seed dormancy is defined as the state or a condition in which the seeds are prevented from germination even under the favourable environmental conditions for germination which includes temperature, water, gas, light, seed coats, and several other mechanical restrictions.
The main reason behind the occurrence of these conditions is that they require the period of rest before being capable of the germination. This condition varies from several days to months and even years. These conditions are the combination of light, water, gases, heat, seed coats and the hormone structures.
Types of Seed Dormancy
The seed dormancy is of the following different types:
Innate Dormancy
It is the condition of the seeds that are incapable of germinating even if the conditions suitable for the seedling growth are supplied. This inability to germinate can be due in some certain species to the embryo being immature during the time of the dispersal.
Enforced Dormancy
It is the condition of the seeds that are incapable of germinating because of an environmental restraint that includes an adequate amount of moisture, light, oxygen, and a suitable temperature.
Induced Dormancy
This type of seed dormancy occurs when the seed has imbibed water but it has been placed under extremely unfavourable conditions for germinating. Finally, the seed fails to germinate even when it is kept under more favourable conditions.
Causes of Seed Dormancy
There are certain major causes of seed dormancy. Here are the few reasons for the seed dormancy that are mentioned below:
Temperature
Light
Hard seed coat
Germinating inhibitors
Period after ripening
Immaturity of seed embryo
Impermeable seed coat to the oxygen
Impermeable seed coat to the water
Mechanical resistance of the seed coat
Presence of the higher concentrate solutes
FAQs on Understanding Photoperiodism Vernalisation and Seed Dormancy in Plants
1. What is photoperiodism in plants?
Photoperiodism is the response of plants to the relative length of day and night, especially in regulating flowering. It enables plants to detect seasonal changes through the duration of light and darkness.
- It is controlled by the pigment phytochrome.
- Plants measure the length of the night, not just the day.
- It influences flowering, seed germination, and dormancy.
2. What are the types of photoperiodism?
The main types of photoperiodism are short-day plants, long-day plants, and day-neutral plants. These categories are based on how plants respond to day length for flowering.
- Short-day plants (SDP): Flower when the night is longer than a critical length (e.g., rice, chrysanthemum).
- Long-day plants (LDP): Flower when the night is shorter than a critical length (e.g., wheat, spinach).
- Day-neutral plants: Flowering is independent of day length (e.g., tomato, cotton).
3. How does photoperiodism control flowering?
Photoperiodism controls flowering by regulating the production of a flowering signal called florigen in response to day and night length. The process involves:
- Detection of light by phytochrome in leaves.
- Measurement of critical night length.
- Synthesis of florigen in leaves.
- Transport of florigen to the shoot apical meristem to initiate flowering.
4. What is vernalisation in plants?
Vernalisation is the induction of flowering by exposing plants or seeds to a prolonged period of low temperature. It allows certain plants to flower after experiencing winter conditions.
- Common in winter wheat, barley, and cabbage.
- Occurs at temperatures typically between 0–10°C.
- Takes place in the shoot apical meristem or embryo.
5. Why is vernalisation important for flowering?
Vernalisation is important because it prevents premature flowering and ensures plants bloom after winter under favorable conditions. It provides seasonal timing control.
- Prevents flowering during autumn.
- Synchronizes flowering in spring.
- Enhances agricultural yield in crops like wheat and rye.
6. What is seed dormancy?
Seed dormancy is a temporary state in which viable seeds do not germinate even under favorable environmental conditions. It acts as a survival strategy.
- Prevents germination during unsuitable seasons.
- Ensures species survival in adverse climates.
- Can be caused by embryo immaturity or seed coat barriers.
7. What are the types of seed dormancy?
The main types of seed dormancy are innate dormancy, induced dormancy, and enforced dormancy. These types differ based on their cause.
- Innate dormancy: Present at the time of seed dispersal due to internal factors.
- Induced dormancy: Develops after dispersal due to unfavorable conditions.
- Enforced dormancy: Caused by absence of suitable environmental conditions like water or oxygen.
8. How can seed dormancy be broken?
Seed dormancy can be broken by treatments that remove physical or physiological barriers to germination. Common methods include:
- Scarification: Breaking or softening the seed coat.
- Stratification: Exposing seeds to cold, moist conditions.
- Light exposure in photoblastic seeds.
- Treatment with growth regulators like gibberellins.
9. What is the difference between photoperiodism and vernalisation?
The main difference between photoperiodism and vernalisation is that photoperiodism depends on day length, while vernalisation depends on low temperature exposure. Key differences include:
- Photoperiodism: Triggered by light and dark duration.
- Vernalisation: Triggered by prolonged cold.
- Photoperiodism mainly involves phytochrome.
- Vernalisation affects the shoot apical meristem.
10. What is the relationship between seed dormancy and vernalisation?
The relationship between seed dormancy and vernalisation is that both involve exposure to low temperature to regulate plant development. However, they act at different stages.
- Seed dormancy: Cold treatment (stratification) promotes germination.
- Vernalisation: Cold treatment induces flowering in mature plants or embryos.
- Both ensure seasonal adaptation and survival.
