Plants, like humans and animals, have natural chemicals that help them grow, develop, and respond to their environment. These special chemicals are called Plant Growth Regulators (PGRs) or Phytohormones. Let’s explore their discovery, types, and importance in a simple and interesting way!
👉 Explore All Topics of NCERT Class XI, Chapter 13: Plant Growth and Development
🌱 What are Plant Growth Regulators?
Plant Growth Regulators (PGRs) are natural or artificial substances that influence plant growth and development. They control various functions like seed germination, flowering, fruit development, and even the falling of leaves.
These regulators can be classified into two types:
- Growth Promoters – Help plants grow faster (e.g., Auxins, Gibberellins, Cytokinins)
- Growth Inhibitors – Slow down growth or stop certain processes (e.g., Abscisic Acid, Ethylene)
🕵️♂️ How Were Plant Growth Regulators Discovered?
The discovery of PGRs was a fascinating journey! Scientists conducted several experiments to understand how plants respond to different stimuli like light and gravity. Let’s look at how some of the major plant hormones were discovered.
🌞 Discovery of Auxins (First Growth Hormone)
- In 1880, Charles Darwin and his son Francis Darwin studied the movement of canary grass towards light. They observed that the tip of the shoot was responsible for bending toward light.
- Later in 1926, F.W. Went extracted a chemical from oat seedlings, which he named Auxin.
- Conclusion: Auxins help in plant bending towards light (a process called Phototropism).
👉 Discover More About Auxins – The Growth Hormone from NCERT
📏 Discovery of Gibberellins
- In 1926, a Japanese scientist named Eiichi Kurosawa found that a fungus called Gibberella fujikuroi caused excessive growth in rice plants.
- Later, scientists identified the growth-promoting substance and named it Gibberellin.
- Conclusion: Gibberellins help in stem elongation and seed germination.
🍏 Discovery of Cytokinins
- In 1955, Folke Skoog and Carlos Miller discovered a substance that helped plant cells divide faster. This was named Cytokinin.
- Conclusion: Cytokinins promote cell division and delay aging in leaves.
🍂 Discovery of Abscisic Acid (ABA)
- In the 1960s, scientists discovered Abscisic Acid (ABA) while studying leaf fall and seed dormancy.
- Conclusion: ABA acts as a stress hormone and helps plants survive harsh conditions by stopping growth.
🍌 Discovery of Ethylene
- Scientists found that fruits ripen faster when exposed to a gas called Ethylene.
- In 1901, Dimitry Neljubow confirmed that ethylene is a natural plant hormone.
- Conclusion: Ethylene helps in fruit ripening and leaf fall.
📝 Summary Table of Plant Growth Regulators
| Plant Growth Regulator | Discovered By | Year | Main Function |
|---|---|---|---|
| Auxin | Charles & Francis Darwin, F.W. Went | 1880, 1926 | Helps in cell elongation, phototropism |
| Gibberellin | Eiichi Kurosawa | 1926 | Promotes stem elongation, seed germination |
| Cytokinin | Folke Skoog, Carlos Miller | 1955 | Encourages cell division, delays aging |
| Abscisic Acid (ABA) | Scientists in 1960s | 1960s | Induces seed dormancy, stress resistance |
| Ethylene | Dimitry Neljubow | 1901 | Helps in fruit ripening and leaf fall |
🎯 Why is This Important for Exams?
- Questions on plant hormones often appear in exams like SSC, RRB NTPC, UPSC, and state-level exams.
- Understanding their discovery, functions, and applications helps in solving objective-type questions easily.
- Learning about plant growth regulators also helps in understanding agriculture, biotechnology, and environmental science.
✨ Fun Facts About Plant Growth Regulators
- Bananas ripen faster when kept near apples because both release ethylene gas.
- Gibberellins help grapes grow bigger! That’s why seedless grapes are larger than normal grapes.
- Abscisic Acid (ABA) helps seeds “sleep” during unfavorable conditions so they can grow later when the environment is better.
- Auxins are used in plant cuttings to grow new roots!
🌿 Final Thoughts
Plant Growth Regulators are nature’s magic chemicals that help plants grow, flower, and survive. Scientists have worked for over a century to discover these amazing hormones, and they continue to play an essential role in agriculture and horticulture. Learning about them is not only helpful for competitive exams but also for understanding the science behind plant life.
