Photoperiodism and vernalization

1. Introduction

1. Plant growth and development are influenced by environmental factors like light and temperature.
2. Photoperiodism is the response of plants to the duration of light and darkness.
3. Vernalization is the process of cold treatment to induce flowering in plants.
4. Both phenomena help plants adapt to seasonal changes and optimize reproduction.

2. Photoperiodism

1. Photoperiodism is the effect of day length on flowering and other physiological processes.
2. Discovered by Garner and Allard in 1920 while studying Maryland Mammoth tobacco.
3. Plants are classified based on their response to light into Short-day plants (SDP), Long-day plants (LDP), and Day-neutral plants (DNP).

2.1 Short-Day Plants (SDP)

1. Require a light period shorter than a critical length to flower.
2. Flower in autumn and winter.
3. Examples: Rice, Tobacco, Chrysanthemum.

2.2 Long-Day Plants (LDP)

1. Require a light period longer than a critical length to flower.
2. Flower in spring and summer.
3. Examples: Wheat, Barley, Spinach.

2.3 Day-Neutral Plants (DNP)

1. Flowering is not dependent on light duration.
2. Examples: Tomato, Cotton, Sunflower.

3. Phytochrome and Photoperiodism

1. Phytochrome is a pigment responsible for sensing light duration.
2. Exists in two forms: Pr (red light absorbing) and Pfr (far-red light absorbing).
3. Pfr is the biologically active form that regulates flowering.
4. In SDPs, high Pfr inhibits flowering.
5. In LDPs, high Pfr promotes flowering.

4. Vernalization

1. Vernalization is the process of exposing plants to low temperatures to induce flowering.
2. First discovered by Lysenko in Russia.
3. It prevents premature flowering and ensures flowering in favorable conditions.
4. Cold treatment is effective in winter crops like wheat, barley, and cabbage.

5. Vernalization Mechanism

1. Occurs at 0°C to 5°C for a specific period.
2. The stimulus is perceived by meristematic tissues in seeds or shoot tips.
3. It triggers the formation of a hypothetical hormone called vernalin.
4. Vernalization can be reversed by exposing plants to high temperatures, a process called devernalization.

6. Importance of Vernalization

1. Ensures proper timing of flowering in temperate crops.
2. Prevents crops from flowering too early in unfavorable conditions.
3. Used in agriculture to improve crop yields and quality.

7. Comparison of Photoperiodism and Vernalization

8. Applications in Agriculture

1. Used to manipulate flowering time for better crop production.
2. Helps in developing cold-resistant crops for temperate regions.
3. Increases yield and quality of certain crops.

9. Conclusion

1. Photoperiodism controls flowering in response to day length.
2. Vernalization enables plants to flower after exposure to cold temperatures.
3. Both processes play a vital role in plant adaptation and crop improvement.