Generally, there are five types of plant hormones, namely, auxin, gibberellins (GAs), cytokinins, abscisic acid (ABA) and ethylene. In addition to these, there are more derivative compounds, both natural and synthetic, which also act as plant growth regulators.

2. PLANT GROWTH REGULATOR
 It is also called plant hormones.
 PGRs are small, simple organic
substances with different chemical
compositions.
 PGRs influences plant physiological
activities like promotion, inhabitation
growth, and modification.

3. TYPES OF PGR
PGR
PLANT GROWTH PROMOTOR PLANT GROWTH INHIBITOR
GIBBERLIN
AUXIN
CYTOKININ
ABA (Abscisic
acid)
ETHYLENE

4. 01
AUXIN

5. DISCOVERY OF AUXIN
Charles Darwin
 The first persons associated with the
discovery of auxins are Charles Darwin
and his son Francis in the early 1880s.
 They were working on Phototropism.

6. THE DISCOVERY OF AUXIN BY FRITZ WENT:
Solation of auxin at the tip of the oat coleoptile in the gelatin block was first
done by Dutch botanist Fritz Went in 1928.

7. TYPES OF AUXIN

8. BIO SYNTHESIS OF AUXIN
IAA (indole-3-Acetic acid) was one of the first auxins to be discovered.
It is the most abundant natural auxin.
There are two types of bio-synthesis processes:
I. TIP (Tryptophan-Independent)
II. TDP (Tryptophan-Dependent)

9. CHORISMATE
ANTHRANILATE
5-PHOSPHORIBOSYL ANTHRANILATE
IGP(INDOLE-3-GLYCEROL PHOSPHATE)
⇌
SERINE INDOLE
IPA IAA
TIP
TRYPTOPHAN
Anthranilate
synthase
Anthranilate
phosphoribosyl
transferase
IGP SYNTHASE
TIP (TRYPTOPHAN INDEPENDENT PATHWAY)
REVERSIBLE REACTION
PLASTIDS
CYTOSOL

10. TDP(TRYPTOPHAN DEPENDENT PATHWAY)
There are 4 possible pathways of TDP
A. IPA Pathway
B. TMA Pathway
C. IAN(Indole-3-acetonitrile) Pathway
D. Bacterial Pathway

11. IPA and TAM PATHWAY
PLASTIDS
TRYPTOPHAN
IPA(INDOLE PYRUVIC ACID)
INDOLE-3-ACETALDEHYDE
INDOLE-3-ACETIC ACID
TRYPTOPHAN
TRANSAMINASE
IPA DECARBOXYLASE
IALD DEHYDROGENASE
TAM (TRYPTAMINE)
CYTOSOL

12. IAN PATHWAY
PLASTIDS
TRYPTOPHAN
INDOLE-3-ACETALDOXINE
INDOLE-3-AUTONITRILE
IAA
NITRILASE ENZYME
CYTOSOL

13. IAM PATHWAY
PLASTIDS
TRYPTOPHAN
INDOLE-3-ACETAMIDE
IAA
BACTERIAL PATHWAY
CYTOSOL

14. PHYSIOLOGICAL EFFECT
1. Apical dominance:
Apical buds present inhibit the growth of lateral
buds.
if we decapitate the apical bud then the lateral
bud can grow.
2. Abscission:
Falling of plant parts/ shading of plant parts from
the plant.

15. 3. Flowering
4. Parthenocarpy
parthenocarpy is the natural or artificially induced production of fruit
without fertilization.
5. Root Initiation
6. Cell division
7. Herbicide/ weedicide
 2,4, D – is used to remove weeds among the monocot plant
 It is used by gardeners to prepare weed-free lawns.

17. INTRODUCTION
 Gibberellins (GAs) are plant hormones that regulate various developmental processes,
including stem elongation, germination, dormancy, flowering, flower development and
leaf and fruit senescence.
 GAs are one of the largest known classes of plant hormone.
 All known gibberellins are tetracyclic and diterpenoid acids that are synthesized by the
terpenoid pathway in plastids then modified in the endoplasmic reticulum and cytosol
until they reach biological active form.
 Gibberellic acid is a dehydroxylated Gibberellins
 Ethylene decreases the concentration of bioactive Gas.

18. Discovery of Gibberellin
 GA was first discovered in 1926 when Kurosawa was studying extracts
from rice plants infected by the fungus Gibberella fujikuroi (Bakanae
disease)
 Rice plants infected by Gibberella fujikuroi were very tall and hence
called foolish plants.
 Extracts from the fungus when applied to other normal plants resulted in
an increase in the plant height.
 Later, three Japanese workers, T. Yabuta, Sumiki, and T. Hayashi, 1935
and 1938 isolated the chemical and named it GA [Gibberellic acid].
 There are more than 136 gibberellins isolated from plant, fungi and
bacteria. They are GA1, GA2, GA3 and so on. GA3 Gibberellic acid is
the most widely studied plant growth regulators.

19. Bioactive GAs
 The bioactive GAs are GA1, GA3, GA4, GA7. The presence
of GA1 in various plant species suggests that it is a common
bioactive GA.
 The 19-carbon forms are in general, the biologically active
forms of gibberellins.
 There are certain structural requirement for gibberellin
activity. A carboxyl group at C-7 is a feature of all biological
active gibberellins.

20. Location of Synthesis
 Apical Tissue(Shoot apex)
 Young Leaves
 Highest level of GAs found in immature seeds and
developing fruits
 Root region

22. Gibberellin Translocation

23. BIOLOGICAL
FUNCTIONS OF
GIBBERELLINS

24. ELONGATION OF INTERNODE
1. Shows a plant lacking gibberellins and has an
internode length of “0” as well as it is a dwarf plant
2. Shows your average plant with a moderate amount
of gibberellins and an average internode length.
3. Shows a plant with a large amount of gibberellins
and so has a much longer internode length because
gibberellins promotes cell division in the stem.
 Promote the elongation of internode{the
loosening of cell wall for stretching}
 The target of the gibberellin action is at
intercalary meristem.
Eg : XGT (Xyloglucan trans glycosylase).

25. Seed Germination
Crops Concentration Method of
Application
Effects on
germination
References
Eggplant 750 mg/L Presoaking of
seed
Accelerated
seed
germination
process
(Rodrigues
and Ono,
2017)
Pea 10 ppm Seed soaking Highest
germination
rate
(Bahadur and
Singh, 2011)
Okra 200 ppm Seed priming Maximum
seed
germination,
seed vigor
index, mean
germination
rate
(Lamichhane
et al., 2021)
Tomato 0.5 ppm Soaking Enhances
germination
(Bahadur and
Singh, 2011)

26. Bolting
 Bolting is the elongation of stem in rosette plants
. Bolting is induced by plant hormones of the
gibberellin family.
 Gibberellins induce sub-apical meristem to
develop faster. This causes elongation of reduced
stem.
 Crops inclined to bolt include basil, beetroot,
spinach, onion etc
 For Cabbage, if we applied 60ppm GA3, increase
stem length, number of leaves per plant, root
length,

27. Vernalization
Vernalization or low temperature requirement of some plants can be replaced by gibberellins

28. Dormancy, Fruit development and Fruit growth

29. Delayed Ripening And Malt production

30. Effects of GA3 on sex expression
Effects of GA3 on sex expression Treatment with growth regulators has been found to change sex
expression in cucurbits, okra and pepper. Female inducing hormones are auxin and ethylene whereas
male inducing hormone is GA3. GA3 have been used for maintenance of gynoecious lines in
cucurbits.

31. CYTOKININS
Presented by : Ranit Sarkar

32. INDEX
• Discovery
• Isolation
• Occurrence
• Chemical composition
• Functions
• Uses

33. Discovery
• Discovery: Folke Skoog (F . Skoog) and colleagues in the 1950s
• Skoog observed proliferation of tobacco callus with the addition of cytokinin with extracts of vascular tissues,
yeast extracts, coconut milk, and herring sperm DNA.
• Miller et al. discovered the first cytokinin from degraded product of autoclaved herring sperm
DNA which had power full cytokinesis (division of cytoplasm) promoting effect. It is called kinetin
(N6 – furfuryl amino purine)
• it is a synthetic product does not occur naturally in plants.
test tube which
had DNA showed
maximum cell
division

34. Isolation:
• Another chemical called zeatin was identified from the maize kernel. It is also an adenine derivative
of cytokinin. It was the first identified naturally occurring cytokinin.
• Letham in 1963 isolated zeatin from immature corn kernels. He extracted zeatin from
maize endosperm.

35. Occurrence
Cytokinins occur in regions where rapid cell division occurs such as root
apices, developing shoot buds, young fruits etc.

36. Bio-synthesis
1. The levels of cytokinin in cells are regulated by its biosynthesis and degradation.
2. Isoprenoid cytokinin is formed by transferring the isopentenyl chain to AMP, ADP, or ATP using the enzyme
isopentenyl transferases (IPTs) of two different categories: adenylate IPT and tRNA-IPT.
3. Plant IPT prefers ATP or ADP, while cyanobacterial IPT prefers AMP.
4. Most cytokinin synthesis in plants is catalyzed by adenylate IPT, whereas tRNA-IPT is the enzyme catalyzing
most cytokinin synthesis in cyanobacteria.
5. Isopentenyl AMP, -ADP, and -ATP are converted to ribosides cytokinins by hydroxylation of the isopentenyl side
chain using the enzyme cytochrome P450 monooxygenase.
6. Cytokinin interconversion continues to maintain and regulate the level of active compounds, and conjugates are
formed by O and N glycosylations in the cytokinin.

37. Chemically:
Cytokinins
Natural
Kinetin
Zeatin
Synthetic Thidiazuron

38. 1. They regulate cell division.
2. Cell and organ enlargement.
3. Cytokinin modifies apical dominance and promotes lateral growth.
4. Cytokinin delays senescence.
5. It promotes nutrient mobilization.
6. It promotes chloroplast development.
7. They help to produce new leaves and adventitious shoots.
8. Promoting parthenocarpy
Functions
• Cytokinin = More mitosis
• More mitosis = More cells
• More cells = plant Growth

39. Source
Fig: Nutrient mobilisation
Fig: Lateral growth
Fig: Delays senescence
(Richmond Lang effect)
Fig: New leaves and shoots Fig: Seedless watermelon Fig: Chloroplast

40. Uses and applications
1. Overcoming Senescence: cytokinin are used to delay the senescence of intact leaves and
other plat parts
2. Tissue Culture: Cytokinins along with auxins are essential in tissue culture as they are required
for cell division and morphogenesis/ organogenesis.
Auxin concentration
Auxin concentration
Auxin concentration
Cytokinin
concentration
Cytokinin
concentration
Cytokinin
concentration
Callus
Root
Shoot

41. Cytokinin
Occurrence
Root apices
Developing
shoot buds
Young Fruits
Functions
Growth of shoot
Delay
senescence
Growth of
leaves
Cell division
Overcome apical
dominance
Uses
Overcoming
senescence
Tissue culture

42. Ethylene (C2H4) is a simple, natural, gaseous plant hormone.
It is produced by higher plants, bacteria, and fungi and influences
many aspects of plant growth and development.
Low concentration of 0.1 - 1.0 microliters is sufficient to trigger the
ripening process in climacteric fruits.
Ethylene

43. Functions
Stimulates the release of dormancy.
Stimulates shoot and root growth and differentiation (triple response)
May have a role in adventitious root formation.
Maintains apical hook in seedlings.
Stimulates leaf and fruit abscission.
Stimulates Bromeliads flower induction.
Induce femaleness in dioecious flowers.
Stimulates flower opening.
Stimulates flower and leaf senescence.
Stimulates respiration rate
Stimulates fruit ripening.

44. OCCURRENCE, DISTRIBUTIONAND TRANSPORT OF
ETHYLENE
Ethylene can easily be synthesized in all plant organs such as roots, stems, leaves, tubers,
fruits and seeds.
It is highest in senescing tissues and ripening fruits.
Within the plant organs, ethylene formation is mainly located in peripheral tissues.
Ethylene is biologically active at low concentration (less than 1 ppm)..
Being a gas, ethylene moves by diffusion from its site of synthesis.

45. PHYSIOLOGICAL EFFECTS OFETHYLENE
Stimulate Abscission
It induces abscission of leaves and fruits.
The abscission increases with ethylene concentration.
Yellowing
Separation layer
digested
Ethylene

46. PHYSIOLOGICAL EFFECTS OFETHYLENE
In addition to fruit ripening, ethylene is now known to have many other functions as
well. Ethylene;
1.Stimulates the release of dormancy.
2.Stimulates shoot and root growth and differentiation (triple response)
3.May have a role in adventitious root formation.
4.Stimulates leaf and fruit abscission.
5.Stimulates Bromeliads flower induction.
6.Stimulates flower and leaf senescence.
7.Stimulates respiration rate
8.Stimulates fruit ripening.

47. Break seed and Bud dormancy
The dormancy of many seeds such as cereals can be broken by application of
ethylene.Ethylene application increases the rate of germination.
Ethylene treatment sometimes used to promote bud sprouting in potato and other
tubers.
Fruit ripening
It stimulates fruit ripening in most plants including banana, apple, tomato etc.
Growth inhibition
Exogenous application of ethylene inhibits the plant growth. In most dicots, growth of
stem, root and leaves inhibited but the hormone enhances radial growth as a result both
stem and root swell in response to ethylene.
PHYSIOLOGICAL EFFECTS OFETHYLENE

48. Induce Flowering
In most cases ethylene inhibits flowering but in pineapple (Bromeliaceae
family) , mango and litchi it stimulates flowering.
Sex expression
Ethylene stimulate femaleness in plant like cucumber and melons (dioecious).
Normally these plants produce male flowers earlier than female flowers.
Ethylene stimulate the early production of female flowers in these plants.
Plumular Hook Formation
In etiolated dicot seedlings, the plumular tip (shoot apex) is usually bent like a
hook. This hook shape is advantageous to seedling for penetration through the
soil, protecting the tender apical growing point from being injured.
PHYSIOLOGICAL EFFECTS OFETHYLENE

49. Formation of Adventitious Root Hairs
Ethylene induces formation of adventitious roots in plants by diffusing from
different plant parts such as leaf, stem, peduncle and even other roots.
Triple response
Ethylene causes 'triple response' of etiolated seedling (such as in pea) which
consists of:
i) Inhibition of stem elongation (short shoots)
li) Stimulation of radial swelling of stems (fat shoots)
li) Increased lateral growth of roots and Horizontal growth of stems with respect to
gravity (Diageo tropism)
PHYSIOLOGICAL EFFECTS OFETHYLENE

50. ROLEOFETHYLENEIN FRUIT RIPENING
• Ripening is a process in fruits that makes it
acceptable for consumption. The fruit becomes
sweeter, and softer.
• During ripening starch is converted to sugar.
• The fruit is said to be ripe when it attains its full
flavour and aroma
• Ripening causes colour change in the fruit.
• Based on ripening behaviour, fruits are classified
as.
1.Climacteric
2.Non Climacteric

51. INTRO:
Abscisic acid (ABA) is a plant hormone that regulates
numerous aspects of plant growth, development, and stress
responses. ABA-deficient mutants from various plant species display
reduced seed dormancy and wilty phenotypes, highlighting that
these crucial ABA functions are conserved in the plant kingdom
 Abscisic acid (ABA or abscisin II) is a plant hormone.
 ABA is especially important for plants in the response to environmental stresses,
including drought, soil salinity, cold tolerance, freezing tolerance, heat stress and heavy
metal ion tolerance.
 In 1963, abscisic acid was first Identified &characterized as a plant hormone by Frederick
T. Addicott and Larry A. Davis in cotton bolls
 Abscisin II is presently called abscisic acid (ABA).

52. FUNCTIONS
ABA is a key hormone that regulates water status and stomatal
movement. Under drought conditions, plants produce and accumulate
increased amounts of ABA in the guard cells, and this induces stomatal
closure to conserve water
 Inhibits the stomatal opening.
 Act as a signal to reduce shoot growth (under water stress conditions).
 Promote leaf senescence.
 Inhibits seed germination and metabolism of the plant.
 For dropping of fruits from trees, used as a spraying agent.

53.  Fruit ripening is a complex process, which
sees dramatic changes in color, texture, flavor,
and aroma of a fruit.
 Generally, the ripening of climacteric fruit is
regulated by ethylene. However, ABA displays a
similar change as well as ethylene during fruit
maturation.
 Involvement of ABA in fruit ripening and its
relative effect on fruit quality are shown
The involvement of ABA pigment and color
changes, phenolic metabolism, and nutritional
contents, cell wall metabolism and fruit
softening, and sugar and acid
Metabolism in fruit
 The application of ABA by dipping has been used
to observe the role of ABA in mature and unripe
green bananas was greater.
 For pre-harvest spraying, the ABA solution is
sprayed directly on to the fruit surface at the
desired volume.
 It has been sprayed on to grape berries during the
onset of fruit ripening .
 In climacteric fruits such as mangos and peaches,
the ABA solution has been sprayed directly to the
fruits at the beginning of maturation .
ABA APPLICATION IN FRUITS

54.  for High air temperatures coupled with dry winds and rapid soil drying conditions can greatly
reduce stand establishment or impair early growth of vegetable transplants.
 plant growth regulators [abscisic acid (ABA) application on the growth and physiology of pepper
(Capsicum annuum), tomato (Lycopersicon esculentum) and artichoke (Cynara scolymus) seedlings
exposed to one or two cycles of desiccation.
 In pepper, root application of ABA enhanced desiccation tolerance compared to foliar application
 Leaf photosynthesis and conductance decreased upon ABA foliar application up to 2000 mg L
however, photosynthesis rates recovered within a few days of application.
 Throughout two cycles of desiccation on pepper seedlings, ABA had a stronger effect in reducing
stomatal conductance while increasing leaf water potential
 Plant water status was also significantly improved with ABA applied to tomato seedlings.
 Similar physiological responses were measured choke seedlings following foliar ABA (1000 mg L -
1) treatments.
 . Abscisic acid can be an effective physiological tool to mitigate the negative effects of transplant
shock and improve stand establishment of vegetable transplants.
 Understanding the morphological and physiological responses during the transplant shock period
can provide a basis for elucidating the complex mechanisms underlying transplant stress tolerance.
ABAAPPLICATION IN VEGETABLES

55.  Improved crop yield
 Reduced labor costs
 Improved plant health
 Consistent quality
 Cost.
 Time-consuming.
 Limited applicability
 Risk of unintended consequences
PROS CONS