[Biology Class Notes] on Photoperiodism and Vernalisation Pdf for Exam

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. 

[]

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. 

[]

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.