Plant hormones (also called phytohormones) are natural chemicals that control the growth and development of plants.
They act in very small amounts and help plants respond to their surroundings.
Here are the main types of plant hormones and their functions:
1. Auxins
- Promote cell elongation (help plants grow taller).
- Control root growth and phototropism (growth toward light).
- Example: Indole-3-acetic acid (IAA).
2. Gibberellins
- Stimulate stem and leaf growth.
- Help in seed germination and flowering.
- Example: Gibberellic acid (GA₃).
3. Cytokinins
- Promote cell division and growth of new tissues.
- Delay aging of leaves.
- Found in growing areas like buds and roots.
4. Abscisic acid (ABA)
- Called the stress hormone.
- Helps plants survive drought or stress by closing stomata.
- Slows down growth and helps in seed dormancy.
5. Ethylene
- A gas hormone that helps ripen fruits.
- Promotes leaf fall (abscission) and flowering in some plants.
In short:
- Auxins → growth and bending
- Gibberellins → elongation and germination
- Cytokinins → cell division
- Abscisic acid → stress and dormancy
- Ethylene → fruit ripening and aging