Plant hormones

Plant Hormones (Phytohormones) or Plant Growth regulators

• As we discussed in the case of animals, plants also have hormones.
• Hormones are chemical messengers that respond to internal and external stimuli.
• They are produced in small quantities in a part of t he plant and then t ransported through xylem, phloem or by diffusion to other parts.
• They may promote or inhibit growth.

Plant growth promoters

1. Auxins

Let us consider the example of a sunflower growing towards the sunlight.

• Once the plant detects sunlight , the hormone auxin is secreted at the shoot tips .
• The secreted auxins diffuse towards the shady side of the plant
• This makes the cells on the shady side grow longer
• Thus, the plant appears to bend towards light . 

2. Gibberellins

Gibberellins also help in growth

Gibberellins in contrast to auxins help in growth of stem

3.  Cytokinin's

Cytokinin's   play an important role in cell division

They promote cell division

Usually they are present in greater concentrations in fruits and se eds.

The rate of cell division in the plant is higher in the region that has higher concentrations of cytokinins.

This simple means;

Plant growth inhibitors

4. Abscisic acid

Abscisic acid is different from other plant growth regulators as the others are responsible for promoting growth, bu t Abscisic acid stops growth.

• Wilting and yellowing of leaves is an example of the effect of Abscisic acid.

5. Ethylene

When you go to the fruit shop, have you noticed that mangoes are kept wrapped in paper bags? Why is this done?

• Mangoes wrapped in a paper bag will release ethylene .

• Ethylene is an odorless gas.It speeds up the ripening process and is also involved in production of more flowers and fruits.
• Ethylene comes under plant growth inhibitors as the process of growth is stopped and focuses on production and ripening of flowers and fruits.