an outline of plant hormones, their structure, function and physiological effects

1. PHYTOHORMONES
SEMESTER VI- BOTANY
PLANT PHYSIOLOGY
PAPER VI
P.HARITHA
DL BOTANY
TTWRDC (M)
SANGAREDDY

2. What do you observe and
infer???

3. Definition
Characteristics
Classification
Functions of various
hormones

4. What are Plant
Hormones?
What are different types
of hormones and where
are they produced in
plant?

5. Plant hormones are “Organic
compounds synthesized in one
part of the plant and translocated
to another part”.
Plant hormones are also
termed as
- Phytohormones
- Plant growth bio regulators
- Growth substances

6. Endogenously
produced
In less
concentrations
Highly
diffusible
Specific in function
May be stimulatory
or inhibitory in
function
Characteristics of Growth substances

7. Classification of growth
substances
Auxins Cytokinin
Abscisic
acid
Gibberellins
Ethylene
Brassino-
steroids

8. Classes of Plant growth regulators :It is accepted
that there are two major classes of plant
hormones:
Auxins
Cytokinin
Gibberellins
Brassinosteroids
Promoters
Ethylene
ABA
Inhibitors

10. Key features of each Growth substance
Isolation Structure
Mode of
action
Physiological
aspects

11. Auxins
 F.W.Went was first to isolate
Auxins from Avena, Wheat and
Maize.
 Thimman defined Auxin as “ an
organic substance which at
low concentration promote
growth along longitudinal
axis”.
 Auxins occur in all groups of
plants.
 Auxin is made in actively
growing tissue which includes
young leaves, fruits, and
especially the shoot apex,
legume root nodules,
germinating pollen grains
 Made in cytosol of cells
 Transport of auxins is polar
through phloem & parenchyma
by active transport.
 Chemically Auxins are Indole 3
Acetic Acid (IAA)
 The Chemical formula: C10H9NO2
 Molar mass: 175.187 g·mol−1y
 An Auxin is made of
 1. Indole ring
 2. a carboxyl group and
 3. at least 1 carbon atom
between ring and carboxyl group

12. Natural auxins
Indole Acetaldehyde
Indole Ethanol
Indole Aceto Nitrate
These get oxidized to IAA by various
plant enzymes
Synthetic Auxins
Naphthalene Acetic Acid (NAA)
Indole Butyric Acid (IBA)
2,4,Dichloro Phenoxy Acetic Acid (2,4- D)
2,4,5,Trichloro Phenoxy Acetic Acid (2,4,5-
T)
2 Methyl 4 Chloro Phenoxy Acetic acid)
(MCPA)
Indole 3 Propionic Acid (IPA)IBA & IPA – used as Rooting
hormones
2,4,D & 2,4,5-T used as selective
herbicides
NAA- used in horticulture
practices

13. Cell enlargement
Cell division
Apical cell dominance and inhibition of lateral buds
Root formation
Tropisms
Flower formation
parthenocarpy
Abscission of leaves and fruits
Weed killers
Sex expression
Physiological effects of Auxins

15. Mode
of
action
DNA replication,
transcription and
translation
Through
ARC
complex –
RNA
synthesis
Loosening of
cell wall
Nucleic acid
synthesis

16. AUXINS IN AGRI AND HORTICULTURE
 Treating stem cuttings and scions for vegetative propagation.
 control of flowering
 Prevents sprouting of buds
 Defoliation of plants
 Prevent leaf fall
 Thinning of compact fruits
 Weedicide
 Development of parthenocarpic fruits
 Increasing fruit set
 Prevention of premature fruit drop

17. Gibberllins
 Gibberellins are 4 or 5 ringed
diterpenoids which is made of gibbane
carbon skeleton.
 Synthesis of gibberellins is by
Mevalonic acid pathway along with
terpenes, sterols and carotenoids.
 Formula: C19H22O6
 Molar mass: 346.37 g/mol
 Discovered by Kurosawa in Rice
which was affected by ‘Bakane’
disease caused by fungus
Gibberella fujikuroi
 They are found in all parts of
plant but abundant in seeds and
young leaves.
 50 kinds of Gibberellins are
isolated till now, out of which
GA1 & GA 3-9 common in all
plants
 Where as GA2 found only in
fungus.
 Movement of gibberellins is non
polar
 By diffusion it moves through
xylem and phloem

18. PHYSIOLOGICAL EFFECTS OF GIBBERELLINS
Effect on dwarf mutants
Bolting and flowering
Substituting cold treatment
Breaking of dormancy
parthenocarpy
Increase in size of leaves, flowers and fruits
Seed germination
Flowering and sex expression

20. Mode
of
action
Stem/cell
elongation
Affect
RNA and
Protein
synthesis
GA binding
Control
Mitotic
cycle

21. COMMERCIAL USES OF GIBBERLLINS
 GA2, GA3,GA7 used for enhancing Grape cluster and size.
 Production of seedless grapes
 Gibberellins enhance α- amylase in barley, which is used in Beer
industry.
 Promote internodal and stalk length, increase in sugar content in
Sugar cane.
 Flower initiation in certain ornamentals like Poinsettia etc.
 Preharvest spray with gibberellins delays fruit ripening which
help in increased storage period during transport of fruits.

22. CYTOKININS
 Cytokinins are 6 furfuryl aminopurine-
a derivative of Adenine.
 Synthesis by t-RNA cytokinin
synthesis/ free cytokinin synthesis/
T-DNA related CK synthesis
 Chemical formula C10H13N5O
 Molar weight 219.24 g/mol
 Haberlandt first identified a
substance which would trigger
cell divisions
 Miller isolated and named them
Kinetin.
 They occur in all non vascular
and vascular plants.
 Found in apical meristems,
developing seeds, roots, fruit
and cambial tissues.
 In few pathogenic bacteria and
fungi, influence disease process
in host-parasite relationship.
 Cytokinin occur naturally and
synthetic made too
 Synthesized in young leaves,
fruits, seeds, root tips and
translocated by xylem and sieve
tubes.

23. Cell division and morphogenesis
Cell enlargement
Breaking seed dormancy
Counter action of apical dominance effect of
enzymes
Delay in senescence
Resistance to adverse effects
Stomatal movements
Development of inflorescence/ enhance fruit set
and size
PHYSIOLOGICAL EFFECTS OF CYTOKININS

25. Mode
of
action
Nucleic acid
metabolism/
Translation
Binding
factors
Stimulate
respiration
Retard/
delay
senescence

26. ABSCISIC ACID
 ABA is a Sesquiterpenoid, it contains
an asymetric carbon atom which exists
in (+) or (-) entaiomers.
 2 CIS-ABA is active naturally occurring
ABA.
 Formula: C15H20O4
 Molar mass: 264.32 g/mol
 Addicot et al discovered ABA.
 It is a natural growth
inhibiting phytohormone.
 ABA is naturally occurring as
well as synthetic in form.
 ABA & phenolic compounds-
natural inhibitor
 Malic hydrazide, AMO-1618,
Morphactin, Chlorocholine
chloride- synthetic inhibitors.
 ABA is found in all plant
groups except Liverworts and
few algae.
 In Liverworts ABA is
substituted by Lunularic acid.

27.  ABA as a growth inhibitor controls unending
enlargement of internodes of stems, leaves or
any part of the plant.
 From leaves it gets transported to shoot and
root tips through xylem & phloem.
 Movement is Basipetal.
 ABA is also referred as Anti Auxin/ Anti
Gibberellins/ Anti Cytokinin
 Biosynthesis is by 2 ways- Indirect
Xanthophyll cleavage pathway-
higher plants
 Direct pathway – Isoprenoid pathway-
Fungi

28. PHYSIOLOGICAL EFFECTS OF ABA
Growth inhibition
Dormancy
Abscission
Seed development and germination
Fruit growth and flowering
Senescence
Stomatal movements
Root geotropism

30. Mode
of
action
Regulate
enzyme
synthesis
Proton and
Potassium
pump
Stomatal
responses
Inhibition at
translational
level

31. ETHYLENE
 Formula: C2H4
 Molar mass: 28.05 g/mol
 Auxins seem to regulate Ethylene
production.
 Both auxins and ethylene found in
similar parts of plant in high
concentrations
 Discovered by Neljuibow
 A gaseous Phytohormone
 Found in all plants in traces
 Produced in more quantities
in meristematic and growing
regions and nodal parts,
specially produced in large
quantities in fruits
 Non polar transport by
diffusion
 Biosynthetic pathway unclear
 But requires Methionine as a
Precursor.

32. PHYSIOLOGICAL ASPECTS OF ETHYLENE
Abscission
Ripening
Effect on growth
Degreening
Senescence
Flowering
Dormancy

34. Mode
of
action
Induce
Enzyme
changes
RNA
synthesis
Protein
synthesis
Enzyme –
Receptor
complex

35. PRACTICAL APPLICATIONS OF ETHYLENE
 ETHREL(2-chloroethyl-phosphonic acid) is a synthetic ethylene
used commercially
 It helps in acceleration of fruit ripening- Banana, Apples
 Induce flowering in Pineapples
 Cause senescence in Tobacco leaves
 Prolongs storage life of fruits
 Regulate fruit or leaf fall in commercial plants at appropriate
time

36. BRASSIONSTEROIDS  Chemically Polyhydroxy steroids and
has common 5 α-choleston skeleton
and show structural variation in side
chain.
 2 Biosynthetic pathways-Early C6 and
Late C6 oxidation
 Molecular Formula: C28H48O6
 Molecular Weight: 480.7 g/mol
 Regarded as Sixth group of Plant
growth regulators.
 First identified by Mitchell et al
 Discovered in Brassica napus and
later identified in 44 plants
 (37 angiosperms, 5 gymnosperms
and one each in algae and
pteridophyte)
 Show growth promoting activity
 Found in very minute quantities
 Pollen grains and immature seeds
have highest concentration of
brassinosteroids.
 Used in improving yield and growth
of many vegetable yielding plants.

37. PHYSIOLOGICAL EFFECTS OF BRASSIONSTEROIDS
Growth
Germination
Flowering
Senescence
Stress tolerance to abiotic factors

38. Resistance
to chilling
Eg. Rice
Low
temperature
stress
Eg. Maize
Tolerance to
high
temperatures
Eg. Wheat
DIFFERENT KINDS OF
ABIOTIC STRESS
COUNTERED BY
BRASSIONSTREROIDS
Resistance
to drought
stress
Eg. Sugar
beet
Normal
germination of
seeds under saline
conditions
Eg. Eucalyptus
Removal of salt
stress
Eg. Seedlings
of Groundnut

40. Mode
of
action
Signal
transduction
Regulate
gene
expression
Genes
associated
with plant
growth
Activation
of kinase
systems

41. POST GRADUATION
ENTRANCE TEST
AND
HOW TO PREPARE????

48. BOOKS TO PREPARE FOR PG ENTRANCE EXAMS

49. Thank you
Acknowlegdements
I would like to give credit to
authors and owners whose
content I used in the
presentation from the open free
internet portal