How Photoperiodism and Vernalisation Affect Plant Growth
Vernalisation in Plants
Photoperiodism is the reaction of animals and plants to the length of a dark period or especially night. Plants show developmental response to photoperiodism, particularly with the delayed beginning of flowering. In plants, the effects of photoperiodism are classified in short-day plants, long-day plants and day-neutral plants. The short-day plants examples are cotton, marijuana, rice, sorghum, soya beans and green gram. The long-day plants examples are oat, pea, wheat, barley and lettuce. The day neutral plants examples are cucumber, tomato, rose and auto-flowering cannabis (Ruderalis). The process of flowering in these plants does not depend on photoperiodism. Therefore, unlike the short day and long day plants, they initiate the flowering process after reaching a certain developmental stage. In some cases, the process of flowering is in response to some other environmental stimuli such as vernalisation.
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Photoperiodism in Animals
Just like plants, there are certain birds and animals that too show certain behaviour in response to the photoperiod effect. These behaviours include reproduction, migration, shedding of the skin, changing the fur colour, hibernation, aestivation, changing the size of reproductive organs etc. E.g., the canary bird changes the singing frequency depending on the photoperiod.
Also, during the spring season, as there is more daylight, the male bird’s testicles grow in size, which allows more production of androgens which increases the frequency of their song. Whereas, during the autumn season, when there is less daylight, the male canary’s testes regress in size dropping down the production of male hormones and it reduces the frequency of song.
The effect of photoperiodism can be artificially induced on an organism which is practically advantageous to human beings. When an animal is stimulated by light, its pituitary glands release a hormone. This hormone affects the reproduction rate of the organism. Therefore, with the manipulation of daylight, the animals can be made to reproduce even outside its mating season.
In the poultry industry, the application of photoperiodism has proven very effective. It has, therefore, enabled better success in mating, thus increasing the weight and volume of eggs in chicken.
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Vernalisation
This process is the induction of a plant’s blossoming process with exposure to the long duration of cold temperatures of the winter season. The process can be manipulated with the help of an artificial equivalent to the cold season. After the vernalisation process, plants do acquire the ability to blossom flowers; however, they need weeks of growth or additional seasonal cues in order to blossom flowers.
Vernalisation is, at times, used to mean non-woody plants’ requirements of cold dormancy to generate new leaves or shoots. It shows the unfolding of biological events that depend on external factors like a prolonged cold period. However, this use should only be done in coherence with the process of blossoming.
Many plants that grow in the tepid climates depend on vernalisation. They, therefore, must undergo some period of low winter temperature to accelerate or even begin the process of flowering. This process is important from the evolutionary point of view as it ensures that the production of seeds and the subsequent reproductive development takes place in spring and winter. Many species of henbane and thale cress are examples of plants depending on vernalisation.
Similarities Between Photoperiodism and Vernalisation
Both the processes are characterised but the accelerated or scheduled unfolding of certain plants’ and animals’ species. Both these processes affect or positively influence the process of flowering in plants. Photoperiodism influences some physiological processes in animals. Due to the practicality of the processes, they can be induced artificially for the desired outcome; e.g., strawberry plants can be artificially vernalised to grow during seasons that are otherwise non-productive. Similarly, the Suffolk X sheep and young male red deer, when kept on an artificial photoperiod like two cycles of daylength in one calendar year, showed two cycles of intake, gonadal activity and growth.
FAQs on Photoperiodism and Vernalisation: Key Concepts & Exam Tips
1. What is photoperiodism in plants?
Photoperiodism is the physiological response of plants to the length of day or night. It is a developmental process that regulates specific seasonal activities like flowering. This response is crucial for plants to flower at the correct time of year, ensuring reproductive success. The perception of light and dark duration is managed by a specialised photoreceptor pigment called phytochrome in the leaves.
2. What are the different types of plants based on their photoperiodic response?
Plants are generally classified into three main categories based on their photoperiodic requirements for flowering:
- Short-Day Plants (SDP): These plants flower when the day length is shorter than a critical period. Examples include soybean, rice, and chrysanthemum.
- Long-Day Plants (LDP): These plants require a light period longer than a critical length to induce flowering. Examples include spinach, lettuce, and wheat.
- Day-Neutral Plants (DNP): These plants flower irrespective of the day length; their flowering is dependent on other factors like age or temperature. Examples include tomato, cucumber, and sunflower.
3. What is vernalisation and what is its significance?
Vernalisation is the process of inducing a plant's ability to flower by exposing it to a prolonged period of low temperature. Its primary significance is to prevent precocious reproductive development late in the growing season, allowing the plant to survive the winter and flower during favourable conditions in the spring. This is common in biennial plants like cabbage and carrot, and some varieties of wheat.
4. What is the fundamental difference between photoperiodism and vernalisation?
The fundamental difference lies in the environmental stimulus that triggers the response. Photoperiodism is a response to the relative length of light and dark periods (the photoperiod). In contrast, vernalisation is a response to a prolonged period of cold temperature. While both can influence flowering, the stimuli are light duration and cold treatment, respectively.
5. How do plants perceive the stimulus for photoperiodism?
Plants perceive the photoperiodic stimulus through their leaves. A pigment called phytochrome, which exists in two interconvertible forms (Pr and Pfr), acts as the photoreceptor. The duration of light and dark periods determines the ratio of these two forms. This ratio triggers the synthesis of a flowering hormone, believed to be florigen, in the leaves. This hormone is then transported to the shoot apical meristems to initiate the formation of floral buds.
6. How does vernalisation differ from seed dormancy?
While both processes can be influenced by cold and prevent growth, they are fundamentally different. Vernalisation is a specific process that induces flowering competency in a vegetative plant after a cold treatment; it is a developmental switch. In contrast, seed dormancy is a general state of metabolic arrest in a seed that prevents germination even when conditions are favourable. Its purpose is survival over harsh periods, and it can be broken by various factors, not just cold.
7. What is the agricultural importance of understanding photoperiodism and vernalisation?
Understanding these phenomena has significant agricultural applications. By manipulating light exposure in greenhouses, farmers can control the flowering of short-day and long-day plants to meet market demands year-round. Similarly, treating seeds or young plants with cold (vernalisation) can help in growing crops in regions they are not native to and can induce early flowering, shortening the crop cycle and increasing the number of harvests per year.
