role of growth hormones - Auxins in floriculture

Topic division
 Introduction to hormones
 Hormones action
 Auxin and its discovery
 Auxin transport
 Distribution in plants
 Chemical nature
 Auxin types
 Auxin structure
 Bio synthesis
 Physiological role of auxin

HORMONES
Greekword–”tostimulate”.
 Many physiological
reactions are regulated by
action of some chemical.
-“Signal molecules
produced at specific
locations, that occur in
very low concentrations,
and cause altered
processes in target cells at
other locations”

 Growth Bio regulators.
 The synthesis of plant hormones is more diffuse and not always
localized
 Theyelicit specific biochemical, physiological, or morphological
responses
 The concentration of hormones requiredfor the plant response
is very low(10 to 10 M )
-6 -5
HORMONES

It is accepted that there are two major classes of plant hormone
CLASS ACTION EXAMPLES
Promoters Cause faster
growth
Auxin
Cytokinen
Brassinoster
oids
Inhibitors Reduce
growth
Ethylene
ABA
Jasmonic
acid
Classification

• Bud formation
• Flowering time
• Fruit formation and
ripening
• Disease resistance
• Leaf fall
• Seed germination
• Roots and shoots growth
control in plants
What do hormones

o This was the first group of
plant hormones discovered.
o Term "auxin" is derived from
the Greek word "to increase or
grow".
o Auxin is a general name for a
group of hormones that are
involved with growth
responses i.e., elongate cells,
stimulate cell division in callus.

History of Auxins
1.Sachs 1882- First person to suggest that some substance
concerned to that organ formation where synthesized in
leaf and transported to downward from the leaf.

2.Charles Darwin(1880)
First scientist responsible for
conducting the research on
plant growth hormones
In his book -The Power
1st
experiment
:
Conducted on
coleoptile
of canary
grass .Took
this exposed
to
unilateral
light ,
later he
found that
the
2nd experiment :
Removed
the
coleoptile
tip , then
exposed to
unilateral

3rd experiment :
Covered the coleoptile tip with black cap then
exposed to unilateral light.Doesnot bent
towards source of light

By this experiment .He reported that some
stimulanceis transmitted from the tip to the
lowerpart, whichcause bending of coleoptile
towards the source of light.

1st -Tookoat coleoptile and
exposedto unilateral light
which cause bending towards
the sourcelight .
2nd – Removedthe tip , and then
exposed, doesnotmove or bent.
3rd – Replaced the coleoptile tip
on a cut stem. Exposed to
unilateral light causing bending
towards the source of light .
3.Boysen jensen [1910] :
Experiment on oat coleoptile

4th – Inserted a thin gelatin plate between the tip
and cut stem , exposed to unilateral sun light
By this experiment he concluded that, some
substance diffuse from the tip through the thin
gelatin to cut the stem , where cause bending
towards source of light .

 Took the aveana
coleoptile tip, this tip
placed on agar [block]for
certain period of time.
 After some time he cut
the agar block into small
pieces and placed on
avena coleoptile one side
asymmetrically, then
exposed to unilateral
light.
F. W . Went [1912]:
Experiment on oat seedlings

After sometime , it bent towards the source of the light.
Amount of bending depends on the concentrations of
substance in the block.
“
“The scientist successfully isolated the hormone called
AUXIN, Also conducted on test called Avena curvetaure
test”.

 -Isolated a substance from
human urine called it as
Auxin A / Axuinniolic acid .
 -Isolated another substance
in urine 1934 in corn germ
oil , called it as Auxin B /
Auxinolenic acid .
 -Late found that , all this
substance are chemically
similar , hence named as ,
Indoel Acetic acid [IAA] ,true
natural auxin .
Kogl and Haegen
Smith [1931]:
Named it as “auxin”

Where do Auxins exists
• Auxin is made in actively
growing tissue which includes
young leaves, fruits, and
especially the shoot apex.
• Made in cytosol of cells

Transport
 Auxin is transported in a basipetal
direction.
 In other words, auxin moves from
the shoot tip towards the roots and
from the roottip towards theshoot.

Distribution of Auxins:
Distributed throughout theplant ,buthigher concentrationfoundinshoottip , root tip,
Youngleaves andauxillary buds.
 FREE FORM
•Extracted by organic solvents like diethyl
ether and ethyl ether
•Easily diffusible , physiologically active
•E.g. : IAA , indole 3 acetaldehyde, indole 3
pyruvic acid.
 BOUND FORM
•Difficult to extract, need special technique called
autolysis and enzymollysis .
•Not diffusible , physiologically inactive.
•Bound with glucose , proteins amino acid hence
called bound form.
•E.g.: auxin glycosyl ester, ascorbigin..
Within theplants it is found in two forms

Chemical Nature Of Auxin
 It should have one unsaturated ring.
 It should have 1 carboxylic group.
 It should have at least 1 carbon atom between
ring and the carboxylic group.
 It should have both positive and negative ions
and distance between these two is 5.5 A.
O
o

Types of auxin
1. Natural auxin : Synthesized with in the in the plant.
ex: IAA, IBA
2. Synthetic auxin : synthesized in laboratory.
ex: 2,4 –D, 2,4,5 –T, MCPA, PCPA, 2,3,6,-T

Biosynthesis of auxin :
 In 1965 scientist Thiemann demonstrated that a fungus
Rhizopus synius would convert Tryptophan into Indole -3-
acetic acid.
 Tryptophan is a called as primary precursor pf auxin and
synthesized in two steps
 1.Deamination(IPA pathway)
 2.Decarboxylation(TAM pathway)

1.Cell Elongation and Cell Division
 Auxin promotes cell division within the cambial
region.
 The main causes of cell elongation-
– By increasing the osmotic content,
permeability of cell to water, wall synthesis.
– By reducing wall pressure.
– By inducing the synthesis of RNA

Auxin promotes differentiation of vascular
tissue (i.e., xylem and phloem
 Auxin and sugar ----: Vascular tissue
 Auxin and low sugar (1.5 - 2.5%) -----
Xylem
 Auxin and high sugar (4%) ------- Phloem
 Auxin and moderate levels of sugar (2.5 -
3.0%) --- Xylem & Phloem
2.Cell differentiation

 Apical or terminal buds of many vascular
plants are very active while the lateral buds
remain inactive.
 Removal of apical buds promotes lateral buds
to grow.
 Apical dominance is due to much higher auxin
content in the apical buds than lateral buds
Apical Dominance

 Plant bend towards unilateral light.
 This is due to higher concentration of auxin on the
shaded side.
Phototropism

Geotropism
 Movement of a plant’s
organ in response to
gravity is known as
Geotropism/
Gravitropism.
 Stem and roots
accumulate IAA on the
lower side in response to
gravity.

Positive gravitropism:
• Upper side of roots grow more rapidly than the lower
side.
• Roots ultimately grow downward

Negative gravitropism
• Increased auxin concentration on the lower side
in stems causes those cells to grow more than
cells on the upper side.
• Stem bends up against the force of gravity

Parthenocarpy
 Auxin induces Parthenocarpy.
 Spray of hormones on flowers cause
development of seedless fruits specially in case
of fruit and vegetable crops.
 Application of IAA, IBA, and NAA show 100%
success.

• Abscission does not occur when auxin content is
high on distal end and low in the proximal end of
abscission zone.
Control of Abscission
Abscission layer

Root initiation :
 Application of IAA to cut end of a stem promotes
root formation.
Ex : IAA , IBA , NAA
 Most cuttings at-
1000-3000ppm
 Maximum-10,000ppm

Callus Formation
 Undifferentiated mass of parenchymatous tissue is
known as callus.
 Application of IAA causes cells to elongate

Sex Expression
 Auxin induced the changing of sex ratio of
flowers towards femaleness, i.e. increase the
number of female flowers.

Promotion of Flowering
 Application NAA causes uniform flowering,
leading to development of uniform sized fruits.
 2, 4 -D is also used to increase the femaleness in
monoecious flowers.

Germination
 IAA, IBA, is most
widely used in
soaking seeds for
germination

Prevention of Premature Dropping of
Fruits
 In case of Apple and Cotton - NAA
 In case of Citrus fruits – 2,4–D/ 2,4,5-T .
Fruit Setting
• 2, 4, 5-T is used for improved fruit setting in
berries.

Thinning of Flower, Fruit and
Leaves
 2, 4-D is used for defoliation of Cotton plant
before boll harvesting. NAA is used for fruit
thinning in Apple.

Weedicide
 2, 4-D, MCPA (Methyl Chloro-Phenoxy Acetic
Acid) are weed killer.
 2,4-D is highly toxic to broad leaved plants or
dicotyledons.

Tissue Culture
 Auxins along with cytokinin shows successful
callus formation, root-shoot differentiation etc.

Effect of different concentrations of auxins on the
regeneration of chrysanthemum morifolium plantlets.
Kalia.,2015 (Amritsar)

Sl.
no
Treatment
IBA(mg/l)
Shoot
initiation
percentage
Average
length of
shoots(cm)
Average
shoots per
explant
Average
nodes per
explant
1 Control(0.0) 25.3 1.2 1.4 1.9
2 0.2 48.6 1.8 2.6 2.8
3 0.5 30.2 1.3 2.1 2.2
4 0.8 19.7 1.2 1.5 1.7
5 1.0 - - - -
Table1. Effect of different concentrations of IBA on the regeneration
of chrysanthemum from nodal segments.

Sl.
no
Treatment
NAA(mg/l)
Shoot
initiation
percentage
Average
length of
shoots(cm)
Average
shoots per
explant
Average
nodes per
explant
1 Control(0.0) 25.3 1.2 1.4 1.9
2 0.2 42.4 1.6 1.9 2.3
3 0.5 68.9 2.3 2.1 2.9
4 0.8 38.6 1.9 2.0 2.6
5 1.0 29.9 1.8 1.7 2.3
Table2. Effect of different concentrations of NAA on the
regeneration of chrysanthemum from nodal segments.

Influence of indole-3-butyric acid (IBA) on sprouting
and Rooting potential of bougainvillea spectabilis
cuttings.
Mehraj et al.,2013(Bangladesh)

Table 3. Influence of different treatments on the different attributes of
bougainvillea stem cuttings.

Plate 1. Pictorial presentation of the performance of bougainvillea
against different treatments at 45 days after establishment of stem
cuttings (a) Sprouting (b) Rooting

Fig. 1. Effect of different treatments on number on rooting percentage and
survival percentage of rooted cuttings

Effect of Some Auxins on Growth of Damask
Rose Cuttings in Different Growing Media.
Khan et al.,2006 (Pakistan)

PGR (mg/l) Days to
bud sprout
Bud sprout
%
Bud
spread(m)
No. of
leaves
Shoot
length(cm)
T1-control 9.1c 38.1f 6.51g 5.35e 6.30f
T2-25IAA 10.9b 46.1e 7.77f 5.57e 7.35ef
T3-50IAA 11.8ab 49.6e 8.44ef 5.84de 7.773de
T4-75IAA 12.1ab 56.8d 10.19bc 6.52bd 8.78d
T5-100IAA 11.9ab 72.8d 8.33ef 6.94ab 10.53
T6-25NAA 12.0ab 64.1c 11.32a 6.10ce 8.95d
T7-50NAA 11.9ab 78.8a 10.71ab 7.28ab 13.68
T8-75NAA 13.1a 77.5a 9.59cd 7.37a 12.03b
T9-75NAA 12.8a 68.0c 1.03 6.86ac 10.61c
LSD at
P<0.05
1.39 4.52 1.03 0.79 1.39
Table 4. Effect of Growth Regulator Treatments on Plant
Growth Parameters

Table 5. Effect of Different Growing Media on Plant Growth
Parameters

Table 6. Effect of Interaction (Growth Regulator Treatments x Growing Media)
on Plant Growth Parameters.

role of growth hormones - Auxins in floriculture

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