agriculture

1. Concept and Uses of Phytohormones and Their Roles in Field
Crop Production
Submitted by
Sambita Bhattacharyya
Ph.D. Scholar
Student Id- 61158
Submitted to
Dr. Sumit Chaturvedi
Recent Advances in Crop Growth and
Productivity
APA- 702

2. What are hormones
 The word hormone is derived from Greek word ‘Hormao’ , which means ‘set in motion’ or
‘to excite’
 Plant hormones are a group of naturally occurring biochemicals produced in plants
(endogenous) or synthetic substances applied to plants externally (exogenous) which cause
modification in plant growth and development. Plant growth substances produced by the
plants are known as phytohormones.
 The term phytohormones was coined by Thimann (1948).
 Plant hormones are not nutrients but chemicals that in small amount promote and
influence the growth development, and differentiation of cells and tissues.
 Phytohormones also determine the formation of flowers, stems and leaves, shedding of
leaves, and the development and ripening of fruit.

3. Classification of plant growth hormones

4. General role of hormones in plant system
 Germination
 Flowering
 Aging.
 Root growth.
 Distortion and killing of organs.
 Prevention or promotion of stem elongation.
 Colour enhancement of fruit.
 Prevention of leafing, leaf fall or both.
 Many other conditions.

5. Terminologies
Müller, M., & Munné-Bosch, S. (2021).
Hormonal impact on photosynthesis and
photoprotection in plants. Plant
Physiology, 185(4), 1500-1522.

6. Auxin
• Discovered in 1881 by CHARLES AND
FRANCIS DARWIN.
• They reported experiments on the response of
growing plants to light.
• Grass seedlings do not bend if the tip is
covered with a light proof cap.
• They do not bend when a collar is placed
below the tip.
• 30 year later, PETER BOYSEN, JENSEN
AND ARPAD PAAL demonstrated that the
influence was actually a chemical Darwin and Son’s Experiment

7. • In 1926, Frits Went
performed an
experiment that
explained all of the
previous results
• He named the
chemical messenger
auxin
• It accumulated on the
side of an oat seedling
away from light
• Promoted these cells
to grow faster than
those on the lighted
side
• Cell elongation causes
the plant to bend
towards light Went’s Experiment

8. Precursor and synthesis of auxin
• Auxin is probably synthesized from
tryptophan.
• There are 2 major pathways for auxin
biosynthesis
1.Tryptophan dependent pathway
2.Tryptophan independent pathway
Source: Unacademy

9. Classification auxins
There are 2 major classifications of auxins
1. Endogenous- indoleacetic acid, phenolacetic acid
2. Exogenous- naphthaleneacetic acid, indole-3- acetic acid, Indole -3- propionic acid 2,4-D etc
Farcot, E., Lavedrine, C., & Vernoux, T. (2015). A modular analysis of the auxin signalling network. PLoS One, 10(3), e0122231.

10. Major roles of auxin in plant growth and development
• Auxin causes several responses in plants:
• Bending toward a light source (phototropism).
• Downward root growth in response to gravity (geotropism).
• Promotion of apical dominance (the tendency of an apical bud
to produce hormones that suppress the growth of the buds
below it on the stem).
• Flower formation.
• Fruit set and growth.
• Formation of adventitious roots.
• Auxin is the active ingredient in most rooting compounds in
which cuttings are dipped during vegetative propagation.

11. Role of auxin in seed germination
Wakeel, A., Ali, I., Khan, A. R., Wu, M., Upreti, S., Liu, D., ... & Gan, Y. (2018). Involvement of histone
acetylation and deacetylation in regulating auxin responses and associated phenotypic changes in plants. Plant
cell reports, 37, 51-59.

12. Role of auxin in phototropism
Retzer, K., Korbei, B., & Luschnig, C. (2014). Auxin and tropisms. Auxin and its role in plant development, 361-387.

13. Role of auxin in geotropism
Matilla, A. J. (2020). Auxin: Hormonal signal required for seed development and dormancy. Plants, 9(6), 705.

14. Matilla, A. J. (2020). Auxin: Hormonal signal required for seed development and dormancy. Plants, 9(6)

15. Role of auxin in photosynthesis
Müller, M., & Munné-Bosch, S.
(2021). Hormonal impact on
photosynthesis and photoprotection
in plants. Plant Physiology, 185(4),
1500-1522.

16. Role of auxin in reproductive and maturity stages of plants
• AUXIN MARKS THE FLORAL MERISTEM INITIATION SITES AND IS REQUIRED FOR FLORAL
ORGAN DEVELOPMENT
• AUXIN REGULATES BOTH EARLYAND LATE STAGES OF STAMEN AND POLLEN
DEVELOPMENT
• FERTILIZATION AND POSTFERTILIZATION PROCESSES ARE DEPENDENT ON AUXIN
SIGNALING
1. Pollination
2. Seed-to-Pod Communication
3. Parthenocarpy in Crops
4. Fruit Ripening
Source: Sundberg, E., & Østergaard, L. (2009). Distinct and dynamic auxin activities during reproductive
development. Cold Spring Harbor perspectives in biology, 1(6), a001628.

17. Some commercial auxin formulations with trade names

20. CASE STUDIES

22. Grain yield of wheat as influenced by different seed treatments
Karimi, N., Goltapeh, E. M., Amini, J., Mehnaz, S., & Zarea, M. J. (2021). Effect of Azospirillum zeae and seed priming with zinc, manganese and
auxin on growth and yield parameters of wheat, under dryland farming. Agricultural Research, 10, 44-55.

23. Karimi, N., Goltapeh, E. M., Amini, J., Mehnaz, S., & Zarea, M. J. (2021). Effect of Azospirillum zeae and seed priming with zinc,
manganese and auxin on growth and yield parameters of wheat, under dryland farming. Agricultural Research, 10, 44-55.
Yield increase in different treatments as compared to hydropriming

26. Nejad, M. M., Nejad, T. S., & Shokohfar, A. R. (2014). The effects of deficit irrigation and auxin on the yield of forage
sorghum. Journal of Biodiversity and Environmental Sciences (JBES), 4(1), 167-176.

29. Negi, P., Ambhore, A. M., Bobate, S. P., & Tripathi, B. R. B. D. (2023). Response of plant growth regulators on growth
characters and yield of chickpea (Cicer arietinum L.). The Pharma Innovation Journal, 12(7), 1767-1773.

30. Negi, P., Ambhore, A. M., Bobate, S. P., & Tripathi, B. R. B. D. (2023). Response of plant growth regulators on growth
characters and yield of chickpea (Cicer arietinum L.). The Pharma Innovation Journal, 12(7), 1767-1773.

31. CYTOKININ
 The cytokinins were discovered in the search for factors that stimulate plant cells to divide
(i.e., undergo cytokinesis).
 Cytokinins are plant growth hormones/ substances which are primarily involved in inducing
cell division in parenchymatous cells by stimulating the process of mitosis
 The idea that cell division may be initiated by a diffusible factor originated with the Austrian
plant physiologist G. Haberlandt, who, in about 1913, demonstrated that vascular tissue
contains a water-soluble substance or substances that will stimulate the division of wounded
potato tuber tissue. The effort to determine the nature of this factor (or factors) led to the
discovery of the cytokinins in the 1950s.

32. HISTORY
 The idea that cell division may be initiated by a diffusible factor originated with the Austrian plant
physiologist G. Haberlandt, who, in about 1913, demonstrated that vascular tissue contains a water-soluble
substance or substances that will stimulate the division of wounded potato tuber tissue. The effort to
determine the nature of this factor (or factors) led to the discovery of the cytokinins in the 1950s.
 Johannes Van Overbeek found that milky endosperm of immature coconut also had this factor which
stimulated cell division and differentiation in very young Datura embryos.
 Jablonski and Skoog (1954) extended the work of Haberlandt and reported that a substance present in the
vascular tissue was responsible for causing cell division in the pith cells.
 Miller and his co-workers (1954) isolated and purified the cell division substance in crystallized form, from
autoclaved herring fish sperm DNA This active compound was named as Kinetin
 Miller and D.S. Lethem (1963-65) separated naturally occurring kinetin from the milky endosperm of corn
(Zea. Mays. L.) and named as Zeatin.
 Lethem ((1963) proposed the term Cytokinin for such substances.

33. Classifications of cytokinins

34. Synthesis of Cytokinins

35. Structure of Cytokinin

36. Promotion of cell division
Takahashi, Naoki, et al. "Cytokinins control endocycle onset by promoting the expression of an APC/C activator in Arabidopsis roots." Current
Biology 23.18 (2013): 1812-1817.

37. Cell enlargement
Kieber, Joseph J., and G. Eric Schaller. "Cytokinins." The Arabidopsis Book/American Society of Plant Biologists 12 (2014).

38. Role of cytokinin in seed germination

39. Role of cytokinin in chloroplast development
Cortleven, Anne, and Thomas Schmülling. "Regulation of chloroplast development and function by cytokinin." Journal of experimental botany 66.16
(2015): 4999-5013.

40. Mandal, Sayanti, et al. "Cytokinin and abiotic stress tolerance-What has been
accomplished and the way forward?." Frontiers in Genetics 13 (2022): 943025.
Role of cytokinin in abiotic stress tolerance

41. Commercial Cytokinin formulations

42. CASE STUDY

46. GIBBERELLINS
• Gibberellins (GAs) are plant growth regulators that regulate
various developmental processes, including stem elongation,
germination, dormancy, flowering and fruit senescence.
• GAs strongly promotes cell elongation of intact plants
commonly. They are concentrated in the regions like shoot
apex, young leaves, embryos, flower buds, fruits and
immature seeds.
• These include a large range of chemicals that are produced
naturally within plants and by fungi. They have also been
found in algae, mosses, ferns and gymnosperms.

47. HISTORY
• In the 1950s the second group of hormones, the gibberellins
(GAs), was characterized. The gibberellins are a large group
of related compounds (more than 125 are known) that,
unlike the auxins, are defined by their chemical structure
rather than by their biological activity
• Japanese farmers first observed that in the rice fields a few
plants were distinctly taller, seedless and pale in colour.
They called it as “Bakanae or foolish seedling” diseases
because it made the young rice plants grow ridiculously tall.
Hori (1898) worked on and suggested that the agent of this
disease was a fungal pathogen Fusarium.
• Sawada (1912) hinted that the disease might be caused by
something secreted by the fungus. Kurosawa (1926)
discovered that the disease was caused by a substance
secreted by the fungal species Gibberella fujikuroi resulting
to controversy over the true pathogen.

48. Bio synthesis and precursor of GAs
1. They are synthesized from acetate units of 2
2. acetyl coenzyme A by the mevalonic
pathway

49. STRUCTURE OF GIBBERELLINS

50. Seed germination

51. Gibberellins Stimulate Stem Growth in Dwarf and Rosette Plants
Source: Agriplex.cpm

52. Gibberellins Influence Floral Initiation and Sex Determination
Andrew R.G. Plackett, GIBBERELLINS AND PLANT REPRODUCTION, Annual Plant Reviews (2016) 49, 323–358

53. Gibberellins Promote Fruit Set
Long Lu, Effect of gibberellin (GA) and paclobutrazol (PAC) application on fruit set and sugar content in grapevin
Tree Genetics & Genomes 13(1). 2015

54. SEED DORMANCY BREAKING
Anna Collin, Phytohormones - Signaling Mechanisms and Crosstalk in Plant Development and Stress Responses
(pp.77-100) Chapter: 4 Publisher: InTech

58. •How do gibberellins affect plant height and stem elongation?
•Can gibberellins be used to induce flowering in all plant species?
•Are there any adverse effects of using gibberellins in agriculture?
•Can gibberellins be applied to improve crop yields?
•What are the environmental implications of gibberellin use?

59. ABSCISIC ACID
• While studying dormancy a compound Dormin purified from sycamore
(Acer pseudoplatanus ) leaves collected in early autumn.
• Upon discovery that dormin was chemically identical to a substance that
promotes the abscission of cotton fruits, abscisin II, the compound was
renamed abscisic acid (ABA)

60. OCCURRENCE, CHEMICAL STRUCTURE, AND MEASUREMENT OF ABA
ABA is a 15-carbon compound that resembles the terminal portion of some carotenoid molecules
The orientation of the carboxyl group at carbon 2 determines the cis and trans isomers of ABA. Nearly all the naturally occurring
ABA is in the cis form, and by convention the name abscisic acid refers to that isomer. ABA biosynthesis takes place in chloroplasts
and other plastids
Figure: The chemical structures of the S (counterclockwise array) and R (clockwise array) forms of cis-ABA, and the (S)-2-trans form of ABA. The
numbers in the diagram of (S)-cis-ABA identify the carbon atoms.

61. ABA Concentrations in Tissues Are Highly Variable
• ABA biosynthesis and concentrations can fluctuate dramatically in specific tissues
during development or in response to changing environmental conditions.
• In developing seeds, for example, ABA levels can increase 100-fold within a few days
and then decline to vanishingly low levels as maturation proceeds.
• Under conditions of water stress, ABA in the leaves can increase 50-fold within 4 to 8
hours. Upon rewatering, the ABA level declines to normal in the same amount of
time.

62. Seed dormancy
Tuan, P. A., Kumar, R., Rehal, P. K., Toora, P. K., & Ayele, B. T. (2018). Molecular mechanisms underlying abscisic
acid/gibberellin balance in the control of seed dormancy and germination in cereals. Frontiers in Plant Science, 9, 668.

63. ABA Levels in Seeds Peak during Embryogenesis
• During the first phase, which is characterized by cell divisions and tissue differentiation, the
zygote undergoes embryogenesis (ABA levels peak during mid- to late embryogenesis) and
the endosperm tissue proliferates.
• During the second phase, cell divisions cease and storage compounds accumulate.
• In the final phase, the embryo becomes tolerant to desiccation, and the seed dehydrates, losing
up to 90% of its water. As a consequence of dehydration, metabolism comes to a halt and the
seed enters a quiescent (“resting”) state. In contrast to dormant seeds, quiescent seeds will
germinate upon rehydration.

64. ABA Promotes Desiccation Tolerance in the Embryo
• An important function of ABA in the developing seed is to promote the acquisition of desiccation
tolerance.
• During the mid- to late stages of seed development, specific mRNAs accumulate in embryos at
the time of high levels of endogenous ABA. These mRNAs encode so-called late-
embryogenesis-abundant (LEA) proteins thought to be involved in desiccation tolerance.

65. ABA Closes Stomata in Response to Water Stress
The most significant and best known effect of abscisic acid is its control of stomatal closing in water stress or drought plants. It
inhibits K+ uptake by guard cells and promotes the leakage of malic acid. It results reduction of osmotically active solutes so that
the guard cells become flaccid and stomata get closed.

66. Senescence and Abscission
Many workers suggested ABA is an endogenous factor and involved in the senescence and abscission of
leaves and other plant organs. Exogenous application of ABA induces primary yellowing in leaf tissues
in a variety of species ranging from deciduous trees to herbaceous plants. ABA production increases in
senescing leaves once the photosynthetic activity of the leaves decreases below the compensation point.

67. Other activities
• Flowering: ABA acts as inhibitor of flowering in long day plants by
counteracting the effect of gibberellins on flowering in these plants. On the other
hand ABA induces flowering in short day plants
• Geotropism: There are sufficient evidences to support that ABA controls
geotropic responses of roots. Appreciable amounts of ABA have been detected in
maize root tips. The accumulation of ABA in the tip appears to require light and
gravity. It is produced in the root cap, translocate basipetally and stimulates
positive geotropic response by acting as inhibitor.

68. ETHYLENE
• Ethylene is the only plant growth regulator that occurs in
the form of a gas. It is a volatile gas present in the
atmosphere as a component of smoke and other
industrial gases. It is produced by almost all parts of
higher plants and usually present in minute quantity but
causes marked effects. Thus it is not only a gaseous
hydrocarbon but a plant metabolite. Like abscisic acid,
ethylene is usually considered as inhibitory hormone.
• It is a colorless flammable gas with a faint "sweet and
musky" odour when pure and unsaturated hydrocarbon
having double covalent bonds between and adjacent to
carbon atoms.

69. History
• triple response: reduced stem elongation, increased lateral growth (swelling), and
abnormal, horizontal growth.
• The first indication that ethylene is a natural product of plant tissues was published by H.
H. Cousins in 1910. Cousins reported that “emanations” from oranges stored in a
chamber caused the premature ripening of bananas when these gases were passed
through a chamber containing the fruit.
• In 1934, R. Gane and others identified ethylene chemically as a natural product of plant
metabolism
• For 25 years ethylene was not recognized as an important plant hormone, mainly because
many physiologists believed that the effects of ethylene were due to auxin.
• Gas chromatography was introduced in ethylene research in 1959.

70. Site of ethylene production
• Ethylene can be produced by almost all parts of higher plants, although the rate of
production depends on the type of tissue and the stage of development.
• In general, meristematic regions and nodal regions are the most active in ethylene
biosynthesis. However, ethylene production also increases during leaf abscission and
flower senescence, as well as during fruit ripening.
• Any type of wounding can induce ethylene biosynthesis, as can physiological stresses
such as flooding, chilling, disease, and temperature or drought stress.

71. PATHWAY AND PRECURSOR OF ETHYLENE
• METHIONINE is the protein which is activated by ATP and acts as the precursor of ETHYLENE
• methionine is activated with ATP and is converted to S-adenosyl methionine.
• The next step in the biosynthesis of ethylene is the conversion of SAM to 1-amino cyclopropane carboxylic
acid (ACC), which is catalyzed by the enzyme ACC synthase (ACS)
• The final step in the biosynthesis of ethylene is oxidative cleavage of 1-amino cyclopropane carboxylic
acid (ACC) to form ethylene, CO2 and HCN by the enzyme ACCoxidase (ACO).

72. FRUIT RIPENING

73. Seed germination:
Ethylene plays a significant role in breaking seed dormancy and inducing seed
germination in plants like ground nut, wheat, lettuce and cocklebur. It also causes
the increased extension growth of the seedlings in cocklebur (Xanthium
strumarium).The maximum germination however is obtained at about 40-50ppm
ethylene.

74. Epinastic Responses
Ethylene induces epinasty in leaves in flooded /water
logged roots. These roots create anaerobic conditions
and forms aminocyclopropane-1-carboxylic acid
which is transported up by the xylem to the leaf where
it is converted to ethylene in the presence of oxygen
and induce epinasty i.e. the upper side of the petiole of
the leaf grows faster than the lower side and the leaf
curves downwards, which perhaps help the plant to
lose water. Ethylene causes epinasty in tomato, potato,
pea and sunflower.

75. OTHER IMPORTANT EFFECTS
1. Ethylene Induces Lateral Cell Expansion
2. Leaf Epinasty
3. Ethylene Induces the Formation of Roots and Root Hairs
4. Ethylene Breaks Seed and Bud Dormancy in Some Species
5. Ethylene Promotes the Elongation Growth of Submerged Aquatic Species
6. Ethylene Induces Flowering in the Pineapple Family
7. Ethylene Enhances the Rate of Leaf Senescence

76. Inhibitors of ethylene synthesis.
Aminoethoxy-vinylglycine (AVG) and aminooxyacetic acid (AOA)
block the conversion of AdoMet to ACC.
The cobalt ion is also an inhibitor of the ethylene biosynthetic
pathway, blocking the conversion of ACC to ethylene by ACC
oxidase, the last step in ethylene biosynthesis.

77. NEW GENERATION HORMONES
BRASSINOSTEROID
 First discovered in the pollen of Brassica spp.
 Are structurally simillar to steroid hormones.
 Functional overlap with other plant hormones,
especially auxins and gibberellins
 Broad spectrum of physiological effects-Elongation, cell
division, stem bending, vascular tissue development,
delayed senescence, membrane polarization and
reproductive development

78. Salicylicacid
Activate genes in some plants that produce chemicals that aid
in the defense against pathogenic invader.
Jasmonates
 Are produced from fatty acids & seems to promote
the production of defense proteins that are used to
fend off invading organisms.
 Also have a role in seed germination.

79. Plant peptidehormones:-
 Involved in cell to cell signaling.
 Roles in plant growth &development , including defense mechanism.
Polyamines:-
 Are strongly basic molecule with low molecular weight that have been found in all organism studied thus far. Nitric
oxide:-
 Serves as signals in hormonal &defense response.
 E.x-nitrogen fixation , stomata closure , germination , cell death.
Karrikins:-
 Not plant hormones because they are not made by plants, but are a group of plant growth regulator found in the
smoke of burning plant materials that have the ability to stimulates the germination of seeds.
Strigolactones :-
 Implicated in the inhibition of shoot branching.
Triacontanol :-
 Afatty alcohol that acts as a growth stimulant, especially initiating new basal breaks in the rose family.
 It is found inALFALFA(Lucerne),BEE’S WAX.

84. Thank you