Here are the key functions and uses of auxins: Functions: - Stimulates cell enlargement and elongation - Promotes cambial activity and cell division - Induces root formation - Maintains apical dominance by inhibiting bud growth - Inhibits abscission (leaf/fruit dropping) - Mediates tropic responses like phototropism Uses: - Induces rooting in cuttings (horticulture) - Induces parthenocarpy (fruit set without fertilization) - Used as weedicides/herbicides - Promotes flowering in some plants - Extends storage life of fruits and vegetables - Prevents pre-harvest

1. • Plant hormones (also known as phytohormones) are signal molecules produced
within plants, that occur in extremely low concentrations.
• Unlike in animals each plant cell is capable of producing hormones.
• The term ‘Phytohormone' was coined by Went & Thimann and used in the title of their
book in 1937.
• Phytohormones are found across the Plant kingdom , and even in algae, where they have
similar functions to those seen in Higher plant.
• Some phytohormones also occur in microorganism, such as unicellular Fungi and Bacteria,
however in these cases they do not play a hormonal role and can better be regarded
as secondary metabolites.

2. Meristematic
zone
Auxin moves
down the stem
Auxin is
made here
Auxin diffuses down
the shoot stimulating
If one side of shoot is in the
sunlight Auxin diffuses away
from the light
Due to more auxin present
at shady zone shoot to
bend towards light

4. Hormones
As a Signal molecules
Binding with
Receptor
Activated Enzyme
Second
messenger
Transcription
Effect on
cellular
function

6. Brassinosteroids are a class of polyhydroxysteroids, the only example of steroid
based hormones in plants. Brassinosteroids control cell elongation and
division, gravitropism, resistance to stress, and xylem differentiation. They
inhibit root growth and leaf abscission. Brassinolide was the first identified
brassinosteroid and was isolated from extracts of rapeseed
(Brassica napus) pollen in 1979.

7. Jasmonates (JAs) are lipid-based hormones that were originally isolated from
jasmine oil. JAs are especially important in the plant response to attack
from herbivores and necrotrophic pathogen. The most active JA in plants is
jasmonic acid. Jasmonic acid can be further metabolized into methyl-JA, which is
a volatileorganic compound. This unusual property means that methyl-JA can act
as an airborne signal to communicate herbivore attack to other distant leaves
within one plant and even as a signal to neighboring plants. In addition to their
role in defense, JAs are also believed to play roles in seed
germination, the storage of protein in seeds and
root growth.

8. Salicylic acid is a phenolic phytohormone and is found in plants with roles in plant
growth and development, photosynthesis, transpiration, ion uptake and
transport. SA is involved in endogenous signaling, mediating in plant defense
against pathogens. It plays a role in the resistance to pathogens by inducing the
production of pathogenesis-related proteins. It is involved in the systemic
acquired resistance in which a pathogenic attack on one part of the plant induces
resistance in other parts. The signal can also move to nearby
plants by salicylic acid being converted to the volatile
ester methyl salicylate.

9. (SLs) were originally discovered through studies into the germination of the
parasitic weed Striga lutea. It was found that the germination of Striga species
was stimulated by the presence of a compound exuded by the roots of its host
plant. It was later shown that SLs that are exuded into the soil promote the
growth of symbiotic arbuscular mycorrhizal (AM) fungi. More recently, another
role of SLs was identified in the inhibition of shoot branching. This discovery of
the role of SLs in shoot branching led to a dramatic
increase in the interest in these hormones, and it has
since been shown that SLs play important roles
in leaf senescence, phosphate Starvation
response, salt tolerance and light signalling.

10. A.From experiments on coleoptile phototropism, Darwin concluded
in 1880 that a growth stimulus is produced in the coleoptile tip
and is transmitted to the growth zone.
Root
Seed
coleoptile

11. In 1913, P. Boysen Jensen discovered that the growth stimulus passes
through gelatin but not through water impermeable barriers such as
mica.
Mica sheet
inserted on
dark side
Mica sheet
inserted on
light side
Tip
removed
Gelatin

12. coleoptile
Tip
Agar Block
Without
auxin
Transfer tip to agar
block and leave for
several hour
Then transfer a piece
of agar block to fleshy
decapitated coleoptile
Agar with
auxin

13. F.W. Went (1926) by simple experiments demonstrated that the tip of the
coleoptile synthesizes some growth causing substance. He cut the tips of oat
coleoptiles and replaced them in a regularly arranged manner on rectangular
blocks of 5% agar. After an hour the tips were removed and the agar block
was sliced into equal square pieces. When one of these pieces was placed on a
decapitated coleoptile, growth was resumed exactly in a similar manner as if
the coleoptile itself has been replaced. But if ordinary agar blocks were kept
on decapitated tip, growth was not resumed It was thus concluded that some
chemicals migrate down from the coleoptile to the agar blocks and when the
agar block was placed on the decapitated tip these again migrated downwards
and induced growth. He called this chemical substance as auxin.

14. CH2-CH2-CH2-COOH
N
H
CH2CH2CH2COOH
N
H
CH2COOH
CH2COOH
O-CH2COOH
Cl Cl
O-CH2COOH
ClCl
Cl

15. CH2-COOH
N
H

16. CH2-COOH
N
H
CH2-COOH
N
H
Cl
CH2-COOH
indole-3-acetic acid
4-chloroindole-3-acetic acid
phenylacetic acid

17. IsolationDiscovery Distribution Transportation
Auxin (from the Greek auxin=to grow ) is a generic name given to growth hormones produced by the tip of
the coleoptile and specifically required for elongation process
Charles
Darwin
Peter Boysen
F.W. Went
Isolate from dutch
patient suffering
from pellagra
disease (human
urine)Trihydroxy
carboxylic
acid
Auxin A Auxin B Heteroauxin
Isolated from
corn germ oil
Hydroxy-keto
carboxylic acid
Isolated from
Human urine
Beta indole
acetic acid
Found in all Parts of plant
Highest amount(in growing region)
Lowest in non meristematic region
Polar transport
Auxin Influx
(Uptake)
Auxin Efflux

18. IAAˉ
IAAˉ
IAAH
H+
H+
2H+ IAAH
IAAˉ
IAAˉ
IAAˉ
IAAH
H+
H+
H+
H+
PH 7
PH 5
ATP
ATP
ATP
Plasma
membrane
Cell wall
Cytosol
Vacuole
H+
1. IAA enters the cell either passively
in the undissociated form (IAAH) or
by secondary active cotransport in
the anionic form (IAAˉ)
3. In the cytosol which has a neutral
pH, the anionic form (IAAˉ)
predominates
2. The cell wall is maintained at an
acidic pH by the activity of the
plasma membrane H+ ATpase
4. The anions exit the cell via auxin
anion efflux carriers that are
concentrated at the basal ends of the
each cell in the longitudinal pathway
ATP
ATP
H+
influx
carrier
protein
(AUX1)
efflux
Carriers
Pin protein

19. Auxin Influx (Uptake):
According to chemiosmotic model the auxin uptake by plant cells may take place from any
direction. IAA may exist in two forms; one is protonated or un-dissociated form (IAAH) which
is highly lipophilic and can cross the plasma-membrane easily. The other form is dissociated or
anionic form (IAA–) that does not cross plasma-membrane unaided.
i. In more acidic pH (low pH), the IAAH form predominates such as that exists in cell- wall
space (apoplast). The low apoplastic pH (about 5) is maintained due to activities of ATPases
present all around in the plasma-membrane. Any IAA that may be present in cell wall, rapidly
associates with H+ to form IAAH. The latter diffuses passively across the plasma-membrane
easily.
ii. The anionic form (IAA ) may also cross the plasma-membrane from cell wall by secondary
active co-transport mechanism through 2H+/IAA– symporter (i.e., influx carrier protein) which
is uniformly distributed around the cell, These permease type of influx carrier proteins or
2H+/IAA– symporters have been called as AUX1 and were first identified in Arabidopsis roots
by Bennett et al (1996).

20. In cytosol, the pH is relatively higher or neutral (about 7) in comparison to cell wall so that
IAAH dissociates into H+ and IAA. It is in this dissociated form that auxin predominates in
cytosol. In the dissociated or anionic form, the IAA” exits the cell only through basally located
auxin efflux carriers called as PIN proteins The exit of IAA from the cell is driven by inside
negative membrane potential.
The basal location of auxin efflux carriers in each cell in longitudinal pathway establishes
polarity in auxin transport and as mentioned earlier, is one of the two main features of
chemiosmotic model of polar auxin transport.
(Geldner et al (2001) have recently shown experimentally that although PIN proteins are stable
but they do not remain permanently on plasma membrane. Instead, there is actin filaments-
dependent cycling of PIN proteins from plasma membrane to some endosomal compartment
through endocytotic vesicles and their recycling back to plasma membrane).

21. Precursor
IPA IANTAM
Indole-3-pyruvic acid
pathway
Indole-3-acetonitrile acid
pathway
Tryptamine
(Most common pathway) Eg-Tomato Brassicaceae
Poaceae
Musaceae

22. Tryptophan
Indole-3-pyruvic acid
Indole-3-acetaldehyde
Indole-3-acetic acid
(IAA)
Transaminase
IPA
Decorboxylase
Dehydrogenase
Tryptophan
Indole-3-acetaldehyde
Indole-3-acetic acid
(IAA)
Decorboxylation
Dehydrogenase
Tryptamine
Tryptophan
Indole-3-acetaldoxime
Indole-3-acetalnitrite
Tryptophan
monooxygenase
Indole-3-acetic acid
(IAA)
Nitrilase

23. Activation theory Synthesis theory
Intracellular cell
Receptor (ABP)
Intracellular cell
Receptor (ABP)
Intracellular 2nd messenger
H+ transport from cytoplasm to cell wall &P.M
Activation expensin protein
Activate cell wall loosening
Cell expension
Activate H+ pump of P.M
I.S.M
Regulatory protein
Inactive Active
Activate gene responsible for ATPase pump

24. Cell wall
Plasma membrane Expansins
Auxin
stimulates
H+
H+
pump
H+
Cell wall
Cytoplasm
Activates
Cell
elongation
H2O
Cellulose loosens
Cell can elongate
Ankit Mishra

25. Functions of Auxins:
1. Respiration:
2. Metabolism:
3. Solutes:
4. Cell Enlargement
5. Cambial Activity:
6. Cell Division:
7. Tissue Culture:
8. Root Formation:
9. Apical Dominance
10. Inhibition of Abscission:.
11. Tropic Movements:.
12. Sex:
13. Seedless Fruits:
14. Ethylene:
Uses of Auxins:
1. Rooting:
2. Parthenocarpy:.
3. Weedicides (= Herbicides):
4. Flowering:
5. Storage:
6. Pre-Harvest Fruit Drop:
7. Vegetable Crops:
8. Fruits:
9. Prevention of Lodging:
10. Dwarf Shoots: