The document discusses various plant growth regulators (PGRs) including their classification, functions, and applications. There are five major classes of natural plant hormones: auxins, gibberellins, cytokinins, ethylene, and abscisic acid. Auxins, gibberellins and cytokinins promote growth, while abscisic acid and ethylene generally inhibit growth. PGRs are used in agriculture to promote seed germination, flowering, fruit development and stress tolerance in plants.

1. Plant growth
regulators
Mandira S.Bhosale
MSc.sem-1

2. • Plant growth regulators (PGR) are plant hormones
(natural & synthetic) which influences the growth and
development of plant.
• PGR are also non nutrient chemicals when introduce to
plant regulate their growth by various stimulus .
• 5 recognized groups of natural plant growth
regulators :
1) Auxins
2) Gibberellins
3) Cytokinins
4) Ethylene
5) Abscisic acid

3. • Based on their actions, plant growth regulators are
broadly classified into two major groups:
• Plant growth promoters
• Plant growth inhibitors.
• Auxins, Gibberellins, and Cytokinins are grouped into
Plant growth promoters while Abscisic acid and
Ethylene are grouped into Plant growth inhibitors.
• Ethylene can be grouped either into the promoters or
into the plant inhibitors.

4. • Derived from the Greek word "auxein" means- "to
grow/increase".
• Auxins may be defined as growth promoting
substances which promote growth along the vertical axis
when applied in low concentration to the shoot of the
plant.
• Natural auxin: Indole acetic acid (IAA)
• Synthetic Auxins : IPA (Indole Propionic Acid)
IBA (Indole Butyric Acid)
NAA (Napthalene Acetic Acid)
2,4-D (2,4 – Dichlorophenoxy acetic acid)
2,4,5-T (2,4,5 – Trichlorophenoxy acetic acid) etc
Auxins

5. • Discovery of auxins:

6. Role of Auxins :
• Cell elongation and cell division:
• Cell division:
Auxin induces / promotes cell division within the
cambial region.
Application
of IAA in
cell
Fixes to the
binding site
Enhances
proton
pump from
cytosol to
wall
Decreases
the pH of
the cell wall
Activation
of some
enzyme and
loosen the
wall
pressure
Ultimately
decreases
the wall
pressure
H2O enters
into the wall
Increases
the cell
elongation

7. • Phototropism by auxins:

8. • Apical dominance:
higher contents of auxins in apical buds inhibits the
growth of lateral buds. Removal of this apical buds
promotes growth of lateral buds.
• Geotropism :
stem and roots accumulate IAA on lower side on
response towards gravity , but stem shows negative
gravitropism /geotropism and roots shows positive
geotropism.
• Root initiation:
accumulation of auxins in the epidermal cells of roots
causes formation of lateral or secondary roots and also
adventitious roots in some plant species.

9. • Control of abscission :
as the level of auxins are decreases in fruits and
leaves abscission layer is formed at the base of petiole
or fruit stalk and soon it’ll gets break and fruit or leaf
falls.
• Parthenocarpy:
Auxins induces Parthenocarpy.
• Callus formation:
application of IAA induces cell elongation and
adventitious roots and thus by the formation of callus.
• Sex expression:
auxin induced the changing of sex ratio of flowers
towards femaleness.

10. Application of auxin in agriculture:
1. Rooting of cuttings :
application of NAA and IBA in stem cutting causes
vegetative propagation
2. Seedless food production: ( Parthenocarpy)
IAA, IBA, NAA
3. Promotion of flowering:
application of NAA causes uniform flowering and
2.4.D causes female flowering .
4. Prevention of premature falling:
NAA & 2,4 D/ 2,4 T
5. Germination :
IAA & IBA used as soaking seed in germination.

11. • Fruit setting
• Thinning of flower ,fruit and seeds
• Weedicide
• Tissue culture

12. Cytokinin
• Cytokinin are synthesized primarily in actively growing
tissues, particular in roots, embryos and fruits and
transported to other organs, although there are many
minor sites of production as well.
• They are involved primarily in cell growth and
differentiation.
• Cytokinins were discovered by F Skoog, C Miller, and
co-workers during the 1950s as factors that promote
cell division (cytokinesis).
• The first Cytokinin was isolated from herring sperm
in 1955 by Miller. This compound was named as kinetin
because of its ability to promote cytokinesis.
kinetin

13. • Cytokinins are synthesized de novo from 5'-AMP and
diphosphorylated hemiterpene
• Cytokinins can be defined structurally as adenine
derivatives with an isopentenyle based side chain
attached to the N'amino group

14. • Cytokinin transport:
 Cytokinin is mainly synthesized in roots and then
transported passively into the shoot via xylem tissue
along with water and minerals transport stream.
 Various cellular importers and exporters are needed
for efficient mobilization and targeted translation of
coupled high-affinity purine transport

15. Roles of Cytokinin:
A. Control morphogenesis
in plant tissue cultures, Cytokinin is required for the
growth of a callus (an undifferentiated, tumor-like mass
of cells)
ratio of cytokinin and auxin are important in
determining the fate of the callus.
B. Crown Gall
• tumor-like mass of undifferentiated cells that
typically occurs near the crown (junction of root and
stem) of the plant caused by the bacterium
Agrobacterium tumefacien
• Cytokinin favors the formation of crown gall disease
by increasing pathogenicity.

17. • C. Regulates the cell division
- especially by controlling the transition from G2 to
mitosis.
• D. Delay senescence :
senescence is the programmed aging process that
occurs in plants .loss of chlorophyll, RNA, protein and
lipids. Cytokinin application to an intact leaf markedly
reduces the extent and rate of chlorophyll and protein
degradation and leaf drop

18. E. Greening Promotes the light
induced formation of chlorophyll
F. Promote lateral bud development
Cytokinin application to dormant buds will cause them
to grow and helps them to form branching.
G. Promote cell expansion
Cytokinins stimulate the expansion of cotyledons.

19. • Uses
• Agriculture :
1. crop production
2. accelerate plant growth
3. Immunity of plant
• Biotechnology :
1.artificial plant tissue culture
2.morphogenesis
3.induce cell division
• Medicine
• Cosmetics

20. Gibberellins
• Also known as Gibberellic acid .
• Gibberellins (GAS) were first isolated from the
fungus Gibberella fujikuroi in 1926 by Japanese
scientist E. Kurosawa
• G. fujikuroi causes Excessive shoot elongation,
Yellowish green leaves, taller plants with absent or
poorly developed grains.
• They are produced in the shoot apex and in the root
system.
• Stimulate cell division ,cell elongation and breaks seed
dormancy

21. • The most characteristic effects of GA on shoot
growth are increased inter-node extension, increased
leaf-growth and enhanced apical dominance
• Influence many reproductive processes
• Many forms of dormancy are broken by GA. These
include seed dormancy, dormancy of potato tubers and
dormancy of shoot internodes and buds.
• Gibberellins are involved in the natural process of
germination. Usually in germination, the breakdown of
starch to glucose in the endosperm begins just after
the seed is exposed to water. Gibberellins in the seed
embryo gives signal starch hydrolysis through
inducing the synthesis of the enzyme a-amylase.

22. • GA also breaks certain forms of dormancy broken in
natural conditions by exposure to low temperature
(vernalization).
• Retard leaf and fruit senescence.
• Exogenous GA application can induce flowering in
species that require cold treatment to bloom.

23. • Uses :
• Increasing food size of seedless grapes
• Stimulating seed germination and seedling growth
• Promoting male flowers in cucumbers for seed
production.
• Overcomes the cold condition requirements for the
seed.

24. Abscisic acid
• Abscisic acid names says that its role in the
abscission of plant leaves.
• ABA is produced in terminal buds. This slower plant
growth and directs leaf primordia to develop scales to
protect the dormant buds during the cold season.
• ABA also inhibits the division of cells in the vascular
cambium, adjusting to cold conditions in the winter by
suspending primary and secondary growth.
• Causes seed dormancy -inhibition of germination

25. • Abscisic acid is also produced in the roots in response
to decreased soil water potential and other situations
in which the plant may be under stress.
• ABA then translocates to the leaves, where it rapidly
decreases the osmotic potential of stomatal guard
cells, causing and stomata to close.
• The ABA-induced stomatal closure reduces
transpiration, thus preventing further water loss
from the leaves in times of low water availability.
• Induces seeds to synthesize storage proteins.

27. Ethylene
• Ethylene is the most commercially produced organic
compound in the world and is used in many industrial
applications.
• It is also naturally occurring.
• In 1934, Gane identified that plants could synthesise
ethylene and in 1935 Crocker proposed ethylene to be
the hormone responsible for fruit ripening and
senescence of vegetative tissues.
• Apples and pears are examples of fruit that produce
ethylene with ripening.
• Ethylene is responsible for the changes in texture,
softening, color, and other processes involved in
ripening.

28. • During the life of the plant, ethylene production is
induced during certain stages of growth such as
germination, ripening of fruits, abscission of leaves,
and senescence of flowers.
• Ethylene production can also be induced by a variety
of external aspects such as mechanical wounding,
environmental stresses, and certain chemicals
including auxin and other regulators.

29. • Ethylene induced many physiological responses like:
1) Growth effects:
inhibits longitudinal but promotes horizontal growth
2) Geotropic response regulation
3) Apical dominance, together/downstream of auxin
4) Breaks dormancy
5) Gas produced by one plant will affect nearby plants.

30. References:
• https://www.biologydiscussion.com/plant-physiology-
2/growth-regulators/plant-growth-regulators-pgrs-
botany/51722
• https://link.springer.com/article/10.1007/s00299-
020-02612-1
• https://www.slideshare.net/SabahatAli9/plant-
growth-regulators-131624130
• https://www.youtube.com/watch?v=OFwNvmRb8_Y
• https://www.youtube.com/watch?v=VEzDlfIzZCs

31. Thank you!!!

32. • Which hormone is responsible for the seed dormancy?
And which is responsible for breaking the seed
dormancy?
• State any 3 types of auxins.
• Explain how gibberellin work?
• State any 4 application of Cytokinin?
• Why ethylene is called growth regulator and also plant
growth promotor hormone?