Phytohormones

In plants nervous system is absent. So, plants control and coordinate their activities by the action of chemical substances called plant hormones or phytohormones present in them.

The main phytohormones present in plants are:

1. Auxins
2. Gibberellins
3. Cytokinin
4. Ethylene and
5. Abscisic acid

Functions of Auxins

The main functions of auxins are:

1. It promotes formation of root on stem cuttings.
2. It promotes elongation of cells of shoots.
3. It promotes parthanocarpy and growth of fruits.

Functions of Gibberellins

The main functions of gibberellins are:

1. It helps in cell growth of stem, leaves and other parts of a plant.
2. It promotes internodal growth in dwarf plants such as maize and pea.
3. It helps in breaking dormancy of buds and seeds.
4. It promotes seed germination.

Functions of Cytokinin

The main functions of cytokinin are:

1. Like gibberellins, cytokinin also helps in breaking dormancy of buds and seeds.
2. It delays the ageing of leaves and other organs of plants.
3. It promotes cell division and cell elongation in plants.

Functions of Ethylene (or Ethene)

The main functions of ethylene are:

1. It helps in ripening of fruits in plants.
2. It promotes flowering in plants and breaks bud dormancy.
3. It promotes falling of leaves, flowers and fruits in plants.

Functions of Abscisic Acid (A.B.A.)

Abscisic acid is also known as stress hormone because it is produced in plants during adverse conditions such as draught, water logging, cold conditions etc. The main functions of abscisic acid are:

1. It promotes falling of fruits and flowers.
2. It induces dormancy in seeds and buds.
3. It increases resistance of plants to cold, drought, water logging and other adverse environmental conditions.

Test Your Understanding and Answer These Questions:

1. What are functions of auxins in plants?
2. What are functions of ethylene in plants?
3. Mention names of various phytohormones.
4. What are functions of cytokinin in plants?
5. What are functions of gibberellins in plants?
6. What are functions of abscisic acid in plants?
7. How does control and coordination take place in plants?
8. What are phytohormones? Name any two phytohormones.
9. Which hormone is known as stress hormone in plants and why?