What are Plant Growth Regulators (Phytohormones)?

Plants cannot run to a doctor or send nerve signals like animals. Instead, they control their growth and response to the environment using special chemical messengers called Plant Growth Regulators (PGRs) or Phytohormones.

Question (Click to Flip)

What are plant growth regulators?

Answer

Plant Growth Regulators (PGRs) are naturally produced chemical compounds that regulate various aspects of plant growth, development, and response to the environment.

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Key Facts

Promoters: Auxins, Gibberellins, Cytokinins.

Inhibitor: Abscisic Acid (ABA).

Only Gaseous Hormone: Ethylene.

Phototropism Cause: Unequal distribution of Auxins.

The 5 Major Plant Growth Regulators

1. Auxins (IAA)

Function: Promote cell elongation, especially in shoots. Responsible for phototropism (bending toward light).
Produced in: Shoot apical meristems.
Example: Indole-3-acetic acid (IAA).

2. Gibberellins

Function: Promote stem elongation, seed germination, and fruit development. Used commercially to produce seedless grapes.
Produced in: Immature seeds.

3. Cytokinins

Function: Promote cell division (cytokinesis). Delay leaf aging (senescence).
Produced in: Root apices.

4. Abscisic Acid (ABA)

Function: The 'Stress Hormone' — causes stomata to close during drought, promotes seed dormancy, causes leaf fall.
Also called: The inhibitor/dormancy hormone.

5. Ethylene

Function: Promotes fruit ripening. The only gaseous plant hormone.
Application: Used commercially to ripen bananas during transport.

Questions and Answers

What are plant growth regulators?+

Plant Growth Regulators (PGRs) are naturally produced chemical compounds that regulate various aspects of plant growth, development, and response to the environment.

Which plant hormone is responsible for fruit ripening?+

Ethylene is the plant hormone responsible for fruit ripening. It is also the only gaseous plant hormone.

What is abscisic acid known as?+

Abscisic Acid (ABA) is called the 'Stress Hormone' because it helps plants respond to drought, cold, and other stresses.

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