This document discusses plant hormones and plant growth regulators. It describes the main types of plant hormones - auxins, gibberellins, cytokinins, abscisic acid, and ethylene. For each hormone, it provides details on their discovery, natural and synthetic forms, sites of synthesis, and roles in plant growth and development such as cell elongation, division, dormancy, flowering, and fruit ripening. It also discusses the roles of anti-auxins and anti-gibberellins in inhibiting the effects of auxins and gibberellins, respectively.

1. Plant Hormone
Plant Growth regulator
Dr. Krishan K Singh

2. Plant Hormone
Plant hormone are organic compound other then nutrients produce by
plant which is low concentration there physiological process of the
plant.
Plant Growth Regulators
Plant Growth Regulators are chemicals synthesized artificially by
humans; they are involved in plant growth and development.

3. Type of Plant Growth regulator
1. Plant Growth promoter
Auxin (Root initiation, cell elongation)
Gibberellins (cell elongation, cell division)
Cytokinin (cell division, inhibits senescence)
2. Plant Growth inhibitors
Abscisic acid (abscission of leaves and fruits, dormancy induction of
seed and bud)
Ethylen

4. 1. Auxin
• Derived from the Greek word auxein means- to grow/increase
• F.W. Went (1928) isolated the growth substance which the name Auxin.
• Naturally occurring auxin is–IAA (Indole acetic acid).
Synthetic Auxins
1. Indole 3 butyric acid
2. Indole 3 propionic acid
3. Naphthalene acetic acid
4. 2,4 Dichloruphenoxy acetic acid
5. Malic Hydrazide

5. Natural Auxins
1. Indole acetic acid
Anti Auxins
1. Naphthythalamic acid
Active sites of Auxins: Shoot tip region, coleoptile and developing embryos etc.
• The auxins synthesis occurs rapidly in green leaves in presence of light than in the
dark.
• The site of auxin transport is located on the plasma lemma.

6. Role of Auxins
 Promote apical bud dominance.
 Promote the elongation of calls.
 Increases call division in cambium.
 IBA promotes rooting of cutting.
 Induces uniform flowering in pineapple.
 Auxins increase in root and decrease in shoot.
 Foliar spray on potato of NAA 100 ppm at 25 DAT- to increase tuber
yield.
 NAA is used to fruit thinning in apple.

7. 2. Gibberellins
Second important growth hormone found in plant.
It was first known by a Japanese farmer Konishi (1898).
The name gibberellin was used by Yabuta and Sumiki (1938).
Kurosawa working in Farmosa discovered GA in 1926.
There are about 129 gibberellins found in both higher plants and the
Gibberella fungus.
Anti-gibberellins: CCC, Phosphon D, MH, paclobutrazol.

8. Role of Gibberellins
 Enhance seed germination.
 Breaking of dormancy.
 Induction of flowering in long day plant.
 The most important effect of GA is the stem elongation.
 GA has also been used to control flower sex expression in cucumbers
and squash.
 GA induced parthenocarpic.
 Foliar spray 25-50 ppm of GA, in grape just before flowering and
during fruiting enhances the fruit size, sugar content and yield.
 GA application trends in promote maleness in these plants.

9. 3. Cytokinin
The term cytokinin proposed by Letham (1963).
Miller and Skoog identified kinetin.
The first naturally occurring hormone identified-Zeatin
Zeatin is the endogenous cytokinin of maize.
Root tip is an important site of cytokinin Synthesis.
Play a key role in higher plants and moves through xylem.

10. Role of Cytokinin
 Initiation of cell division
 Delay of senescence
 Use in tissue culture
 Induce flowering in short day plants.
 Promote femaleness.
 Promote stomatal opening

11. 4. Abscisic Acid (ABA)
ABA first identified by P.F. Weiring (1965).
ABA is naturally occurring common growth inhibitor.
Biosynthesis of ABA also takes place through mevalonic acid.
ABA is terpenoids.
Role of Abscisic acid (ABA)
 Induces bud dormancy and enhances the process of abscission.
 Stimulates the release of ethylene.
 ABA is called Anti-Gibberellins.
 Controls stomate closing.
 Inhibits other hormones produced by leaves, fruits, root caps, and
seeds.
 It accelerates the senescence phase of growth.

12. 5. Ethylene
• BURG (1962) established that ethylene is the only gaseous growth
regulators.
• It is known as ripening.
• Auxins increases ethylene level in plants and hens it has inhibitory effect
on root elongation.
• Maximum ethylene is formed in ripening fruits and senescing tissues.
• Production increased with increase in respiration rate.
Role of Ethylene
• Induces uniform flowering and ripening in pineapple.
• Responsible for fruit ripening with increase in respiration.
• Inhibits stem elongation and cause abscission of leaves.
• Ethrel/Ethephone-The chemical which releases ethylene.