Plant Hormones and Growth Regulators
PLANT
HORMONES
OR
PLANT
GROWTH
REGULATOR
C
ONTE
N
T
S
•
Introduction
•
Classification
•
Auxin
•
Cytokinins
•
Gibberellins
•
Abscisic
acid
•
Ethylene
•
Previously
asked
questions
•
References
INTRODUCTION
Plant
growth
regulators
may
be
defined
as
any
organic
compounds,
which
are
active
at
low
concentrations
in
promoting,
inhibiting or
modifying
growth
and
development.
The
term
Hormone
is
derived
from
a Greek
root
‘
hormao
’
which
means
‘to
stimulate’
Thimann (1948)
suggested
using the
term
‘
Phytohormone’
for
Hormones
of
plant.
The
naturally occurring
growth substances
are commonly
known as
plant hormones, while
the
synthetic
ones
are called
growth
regulator.
Plant
hormone is an
organic
compound synthesized
in
one
part of the plant and
translocated to
another part,
where in
very
low
concentrations
it
causes
a
physiological
response.
The plant hormones are
identified
as promoters
(
auxins,
gibberellin
and
cytokinin
),
inhibitors
(
abscissic
acid
and
ethylene
).
CLASSIFICATION
There
are
five
major
plant
growth
regulators
which
includes:
1)
Auxin
2)
Cytokinins
3)
Gibberellins
4)
Abscisic
acid
(ABA)
5)
Ethylene
Growth promoters
Growth inhibitors
AU
X
IN
Types
TYPES OF
AU
X
INS
•
Indole
acids:
indole-3-propionic
acid
(
IPA
)
•
Naphthalene
acids
Naphthalene
acetic
Acid
(NAA)
β-Naphthoxyacetic
Acid
(NOA)
•
Chlorophenoxy
acids
2,4-Dichlorophenoxyacetic
acid
2,4,5-Trichlorophenoxyacetic
acid
•
Benzoic
acids
2,4,6-Trichlorobenzoic
acid
3,6-dichloro-2-methoxybenzoic
acid
ROLE OF
A
U
XIN
•
Development
of the
female sex organ
Auxins promotes development of female sex organ in flowers along
with ethylene.
•
Apical
dominance
Growth
of
the shoot
apex
(terminal
shoot)
usually
inhibits
the
development
of the lateral buds on the stem beneath. This
phenomenon is
called
apical
dominance.
•
Fruit
development
Pollination
of the
flowers
of
angiosperms
initiates the
formation
of
seeds.
As
the
seeds mature,
they release auxin to the surrounding
flower
parts,
which develop
into
the
fruit that
covers
the
seeds
Plant
B
has
apical
bud
removed
so
auxiliary
buds
grow.
A
B
•
Root
initiation
and
development
The
localized
accumulation
of auxin
in
epidermal
cells
of the
root
initiates
the
formation
of
lateral
or
secondary
roots.
Auxin
also
stimulates
the
formation
of
adventitious
roots
in
many
species.
Adventitious roots grow from
stems
or leaves rather than
from
the
regular
root
system
of
the
plant.
•
Phototropism
Plant
bend
towards
unilateral
light.
This
is
due
to
higher
concentration
of
auxin
on
the
shaded
side.
Partinocarpy
Induces parthinocarpy. i.e. direct Development of ovary in to fruit
without fertilization.
Evidence
for
the
role
of
auxin
in
adventitious
root
formation
With
synthetic
auxin
Without
synthetic
auxin
Adventitious
roots
growing
from
stem
tissue
Saintpaulia
(
Gesneriaceae
family)
(African
violets)
Phototropism
CYTOKININS
•
This
was
discovered in the course of
studies involved
in
identifying
factors
that stimulate
plant cells to
divide.
•
Cytokinins
were
discovered
by
Folke
Skoog,
Carlos
Miller
and
co-workers
in
1955.
•
F.
skoog
discovered
that
degraded
DNA
after
autoclaving
was able to
induce
cell
division
in
Tobacco
pitch
tissue.
•
After
thorough
analysis of the degeaded
product
of
DNA
it
was
found
that
the
active component was
6-fufuryl amino
–
purine
(6-furfuryladenine)
,
and it
was
named
as
kinetin.
•
The
naturally
occurring
cytokinins
are
cis-
trans-zeatin
(ZEA),
dihydrozeatin,
isopentenyladenine(IPA)
etc.
•
The
synthetic
Cytokinins
are
kinetin,
N-N
diphenylurea,
6-benzylaminoprine(BAP)
etc.
naturally
occurring
cytokinins
Synthetic
Cytokinins
ROLE
OF
CYTOKININS
•
Regulates the cell cycle/cell
division
(hence,the
name
"cytokinins)
–
especially
by
controlling
the
transition
from
G2
to
mitosis.
•
Control
morphogenesis
In plant
tissue
cultures,
cytokinin
is required
for
the
growth of
a callus (an undifferentiated, tumor-like
mass
of
cells).
•
Greening
Promotes
the
light-induced
formation
of
chlorophyll.
•
Bud
development
Direct
application
of
cytokinin
promotes
the
growth
of
axillary
buds.
•
Delay
senescence
senescence is
the
programmed aging process that occurs in
plants (and other
organisms
for
that
matter).
loss
of
chlorophyll,
RNA,
protein
and
lipids.
cytokinin
application to
an
intact leaf markedly reduces
the
extent and
rate of
chlorophyll
and
protein degradation
and
leaf
drop.
It
delays
the
ageing
of
the plant.
Transgenic
SAG12-IPT
plant
Nicotiana
(Solanaceae
family)
(Tobacco
plant)
Comparison
of
a transgenic
SAG12-IPT
plant
with
the
wild
type,
Note
the
significantly
delayed
leaf
senescence
in
the
transgenic
plant.
GIBB
E
RELLINS
•
Gibberellins (GAs) were first isolated from
the
fungus
Gibberella fujikuroi
in 1926 by Japanese scientist
E.
Kurosawa
•
G.
fujikuroi
causes
baka’nae
(foolish
seedling) disease in
rice,
causing
Excessive
shoot
elongation,
Yellowish
green
leaves
taller
plants
with
absent or
poorly
developed
grains
Frequent
lodging
due
to
long stature
•
Chemical was extracted &
purified
and
named
as
Gibberellic
A
c
id
(GA).
•
Now
80
different
Gibberellins
are
available-
GA1
to
GA80
is
available.
•
The
most
commonly
occurring
gibberellins
is
GA3.
Gibberellic
acid(GA
3
)
ROLE
OF
GIBBERELLINS
•
Promotes
stem
elongation
When
applied
to
intact
plants,
GA
usually
causes
an
increase,
unlike
auxin.
It
overcomes
dwarfism
in
mutants
.
•
Overcomes
dormancy
in
seeds
Dormancy
is a period in an
organism's
life cycle when growth,
development, and (in
animals)
physical
activity
are
temporarily
stopped.
Gibberellins also have a fundamental role in breaking seed
dormancy
and
stimulating
germination.
Many forms of dormancy are broken by
GA.
These include
seed
dormancy,
dormancy of
potato tubers
and dormancy
of
shoot
internodes
and
buds.
•
GA
can
induce
fruit enlargement
External
application
of gibberellins
can also
enlarge
fruit
size
in
grapes
•
Sex
expression
In
plants
with
separate
male
and
female
flowers,
GA
application
can
determine sex.
For
example, in
cucumber
and
spinach,
GA
treatment
increases
the
proportion
of
male
flowers.
In
maize,
GA
treatment
causes
female
flower
development.
•
Involved
in
parthenocarpic
fruit
development
Development of
fruit
without fertilization . The
fruit
resembles
a normal
fruit,
but
it
is
seedless
GA
causes
ovaries
to mature
without
fertilization
and
produces
bigger
fruits.
•
Germination
Gibberellins are
involved
in the natural process of
germination.
Before
the
photosynthetic apparatus develops sufficiently in
the
early
stages
of
germination, the
stored
energy
reserve
of starch
nourish
the
seedling.
•
Flowering
Exogenous GA
application
can
induce
flowering
in
species
that
ordinarily
require cold
treatment to
bloom.
ABS
C
ISIC
AC
I
D(
A
BA)
•
ABA plays a major role in adaptation to abiotic
environmental stresses, seed
development,
and
germination.
•
Abscisic
acid
is
an
important
growth
regulator
for
induction
of
embryogenesis.
•
This
is
a
growth
inhibitor.
ROLE
O
F
ABSCISIC
ACID
•
Seed
Dormancy
ABA
plays
a
major
role
in
seed
dormancy
D
u
ring
se
e
d mat
u
ration,
ABA
le
v
els
inc
r
e
a
se
dramatically.
This inhibits germination and turns on the
production
of
proteins
that enable
the
embryo
to
survive
dehydration
during
seed
maturation.
ABA
induces
stomatal
closure
Solutes
(
e.g.
potassium
and
chloride
ions)
accumulate
in
guard
cells
causing
water
to
accumulate
in
guard
cells,
making them
turgid(swollen
from
water
uptake.)
ABA
is
one
signal
that
causes
guard
cells
to
release
solutes
and
thus
release
water,
making
them
flaccid(compressed/shrink)
and
closing the
stoma (pore) between
them
•
Drought
resistance
•
Abscisic
acid
is
the
key internal
signal
that facilitates
drought
resistance
in
plants
•
Un
d
er
wat
e
r
st
r
ess
con
d
iti
o
n
s
,
ABA
a
c
cu
m
u
l
ates in
leaves
and
causes stomata to close
rapidly,
reducing
transpiration
and preventing
further
water
loss.
•
ABA causes the opening of
efflux
K+ channels in guard
cell plasma membranes, leading to a
huge loss
of this ion
from
the
cytoplasm.
•
The simultaneous osmotic loss of water leads to a
decrease in
guard
cell’s
turgidity,
with
consequent
closure
of
stomata.
•
Inhibition
of
bud growth
and
shoot
formation.
•
Abscisic
acid
owes
its
names
to its
role in
the
abscission
of
plant
leaves.
•
In
preparation
for
winter,
ABA
is
produced
in
terminal
buds.
•
This
slows
plant
growth
and directs leaf primordia to
develop scales to protect
the
dormant buds
during the
cold
season.
ETHYLENE
•
It is
the
only
gaseous
hormone
of
plants.
•
It is produced naturally by higher plants
and
is able to
diffuse
readily,
via intercellular spaces,
throughout
the
entire
plant
body
•
In
1934,
Gane
identified
that
plants
could
synthesise
ethylene and in 1935 Crocker
proposed
ethylene to be the
hormone
responsible for fruit
ripening and senescence of
vegetative
tissues.
•
Apples
and
pears
are
examples
of fruit
that
produce
ethylene
with
ripening.
•
Ethylene is
responsible for the
changes in texture,
softening,
color,
and
other
processes
involved
in
ripenining.
ROLE
OF
ETHYLENE
•
Fruit
ripening
•
Under natural
conditions, fruits
undergo
a series of changes,
including changes in
colour,
declines in
organic
acid
content
and
increases
in
sugar
content.
•
In
many
fruits,
these
metabolic processes
often
coincide
with a period
of
increased respiration,
the
respiratory
climacteric
.
•
During
the climacteric there is
also a
dramatic increase in
ethylene
production.
•
Ethylene
can
initiate
the climacteric in a number of
fruits
and
is used
commercially
to
ripen
tomatoes,
avocados,
melons,
kiwi
fruit
and bananas.
•
Shoot
Growth
Applied ethylene has
the
capacity to influence
shoot
growth.
Application of ethylene to
dark-grown seedlings
can
cause reduced elongation of the stem, bending of the
stem
and swelling
of
the
epicotyl
or
hypocotyl.
Ethylene
treatment
of
seedlings
promotes
hook
closure
and stem
thickening rather than
elongation. These
etiolated pea
seedlings
were
treated
with
0,
0.1
and 1 ppm ethylene
(left
to
right)
•
Flowering
The
ability
of
ethylene
to
affect
flowering
in
pineapples
has
important
commercial
applications
.
•
Growth
effects
Inhibits
logitudinal but
promotes
horizontal
growth.
•
Breaks
dormancy
REFERENCES
•
Chawla H.S(2009 ) ,
Introduction
to
plant
biotechnology(3
rd
edition), Science
publishers,
22-
23
•
Edwin
F.
George, Edwin
F.
George, Michael A.
Hall, Geert-Jan De Klerk (2007) - Plant
Propagation
by
Tissue
Culture.The
Background,
Volume
1,Springer,175-282
Thank
you
Plant growth regulators, also known as plant hormones, play a crucial role in regulating growth and development in plants. They are organic compounds that act at low concentrations to promote, inhibit, or modify growth processes. The main plant hormones include auxins, cytokinins, gibberellins, abscisic acid, and ethylene. Each hormone has specific functions such as promoting female sex organ development, influencing apical dominance, and regulating fruit development. Understanding these hormones is essential for improving plant growth and productivity.
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Presentation Transcript
PLANTHORMONES OR PLANT GROWTH REGULATOR
CONTENTS Introduction Classification Auxin Cytokinins Gibberellins Abscisic acid Ethylene Previously asked questions References
INTRODUCTION Plant growth regulators may be defined as any organic compounds, which are active at low concentrations in promoting, inhibiting or modifying growth and development. The term Hormone is derived from a Greek root hormao which means to stimulate Thimann (1948) suggested using the term Phytohormone for Hormones of plant. The naturally occurring growth substances are commonly known as plant hormones, while the synthetic ones are called growth regulator. Plant hormone is an organic compound synthesized in one part of the plant and translocated to another part, where in very low concentrations it causes a physiological response. The plant hormones are identified as promoters (auxins, gibberellin and cytokinin), inhibitors (abscissic acid and ethylene).
CLASSIFICATION There are five major plant growth regulators which includes: 1)Auxin 2) Cytokinins 3) Gibberellins 4)Abscisic acid (ABA) 5) Ethylene Growth promoters Growth inhibitors
TYPES OFAUXINS Indole acids: indole-3-propionicacid (IPA)
Naphthalene acids Naphthalene aceticAcid (NAA) -Naphthoxyacetic Acid (NOA)
Chlorophenoxy acids 2,4-Dichlorophenoxyacetic acid 2,4,5-Trichlorophenoxyacetic acid
Benzoic acids 2,4,6-Trichlorobenzoicacid 3,6-dichloro-2-methoxybenzoic acid
ROLE OFAUXIN Development of the female sex organ Auxins promotes development of female sex organ in flowers along with ethylene. Apical dominance Growth of the shoot apex (terminal shoot) usually inhibits the development of the lateral buds on the stem beneath. This phenomenon is called apical dominance. Fruit development Pollination of the flowers of angiosperms initiates the formation of seeds. As the seeds mature, they release auxin to the surrounding flower parts, which develop into the fruit that covers the seeds
A B Plant B has apical bud removed so auxiliary buds grow.
Root initiation and development The localized accumulation of auxin in epidermal cells of the root initiates the formation of lateral or secondary roots. Auxin also stimulates the formation of adventitious roots in many species. Adventitious roots grow from stems or leaves rather than from the regular root system of the plant. Phototropism Plant bend towards unilateral light. This is due to higher concentration of auxin on the shaded side. Partinocarpy Induces parthinocarpy. i.e. direct Development of ovary in to fruit without fertilization.
Evidence for the role of auxin in adventitious root formation Withsynthetic auxin Withoutsynthetic auxin Adventitious rootsgrowing from stem tissue Saintpaulia(Gesneriaceae family) (African violets)
CYTOKININS This was discovered in the course of studies involved in identifying factors that stimulate plant cells to divide. Cytokinins were discovered by Folke Skoog, Carlos Miller and co-workers in 1955. F. skoog discovered that degraded DNA after autoclaving was able to induce cell division in Tobacco pitch tissue. After thorough analysis of the degeaded product of DNA it was found that the active component was 6-fufuryl amino purine (6-furfuryladenine), and it was named as kinetin. The naturally occurring cytokinins are cis- trans-zeatin (ZEA), dihydrozeatin, isopentenyladenine(IPA) etc. The synthetic Cytokinins are kinetin, N-N diphenylurea, 6-benzylaminoprine(BAP) etc.
ROLE OF CYTOKININS Regulates the cell cycle/cell division (hence,the name "cytokinins) especially by controlling the transition from G2 to mitosis. Control morphogenesis In plant tissue cultures, cytokinin is required for the growth of a callus (an undifferentiated, tumor-like mass of cells). Greening Promotes the light-induced formation of chlorophyll. Bud development Direct application of cytokinin promotes the growth of axillary buds.
Delay senescence senescence is the programmed aging process that occurs in plants (and other organisms for that matter). loss of chlorophyll, RNA, protein and lipids. cytokinin application to an intact leaf markedly reduces the extent and rate of chlorophyll and protein degradation and leaf drop. It delays the ageing of the plant.
Transgenic SAG12-IPT plant Nicotiana (Solanaceae family) (Tobaccoplant) Comparison of a transgenic SAG12-IPTplant with the wild type, Note the significantly delayed leaf senescence in the transgenic plant.
GIBBERELLINS Gibberellins (GAs) were first isolated from the fungus Gibberella fujikuroi in 1926 by Japanese scientist E. Kurosawa G. fujikuroi causes baka nae (foolish seedling) disease in rice, causing Excessive shoot elongation, Yellowish green leaves taller plants with absent or poorly developed grains Frequent lodging due to long stature Chemical was extracted & purified and named as GibberellicAcid (GA). Now 80 different Gibberellins are available- GA1 to GA80 is available. The most commonly occurring gibberellins is GA3.
ROLE OF GIBBERELLINS Promotes stem elongation When applied to intact plants, GAusually causes an increase, unlike auxin. It overcomes dwarfism in mutants .
Overcomes dormancy in seeds Dormancy is a period in an organism's life cycle when growth, development, and (in animals) physical activity are temporarily stopped. Gibberellins also have a fundamental role in breaking seed dormancy and stimulating germination. Many forms of dormancy are broken by GA. These include seed dormancy, dormancy of potato tubers and dormancy of shoot internodes and buds. GAcan induce fruit enlargement External application of gibberellins can also enlarge fruit size in grapes
Sex expression In plants with separate male and female flowers, GA application can determine sex. For example, in cucumber and spinach, GAtreatment increases the proportion of male flowers. In maize, GAtreatment causes female flower development. Involved in parthenocarpic fruit development Development of fruit without fertilization . The fruit resembles a normal fruit, but it is seedless GAcauses ovaries to mature without fertilization and produces bigger fruits.
Germination Gibberellins are involved in the natural process of germination. Before the photosynthetic apparatus develops sufficiently in the early stages of germination, the stored energy reserve of starch nourish the seedling. Flowering Exogenous GAapplication can induce flowering in species that ordinarily require cold treatment to bloom.
ABSCISICACID(ABA) ABA plays a major role in adaptation to abiotic environmental stresses, seed development, and germination. Abscisic acid is an important growth regulator for induction of embryogenesis. This is a growth inhibitor.
ROLE OFABSCISICACID Seed Dormancy ABAplays a major role in seed dormancy During seed maturation,ABAlevels increase dramatically. This inhibits germination and turns on the production of proteins that enable the embryo to survive dehydration during seed maturation.
ABA induces stomatal closure ABA is one signal that causes guard cells to release solutes and thus release water, makingthem flaccid(compressed/shrink) and closing the stoma (pore) between them Solutes (e.g. potassium and chloride ions) accumulate in guard cells causing water to accumulate in guard cells, making them turgid(swollen from water uptake.)
Drought resistance Abscisic acid is the key internal signal that facilitates drought resistance in plants Under water stress conditions, ABA accumulates in leaves and causes stomata to close rapidly, reducing transpiration and preventing further water loss. ABA causes the opening of efflux K+ channels in guard cell plasma membranes, leading to a huge loss of this ion from the cytoplasm. The simultaneous osmotic loss of water leads to a decrease in guard cell s turgidity, with consequent closure of stomata.
Inhibition of bud growth and shoot formation. Abscisic acid owes its names to its role in the abscission of plant leaves. In preparation for winter, ABA is produced in terminal buds. This slows plant growth and directs leaf primordia to develop scales to protect the dormant buds during the cold season.
ETHYLENE It is the only gaseous hormone of plants. It is produced naturally by higher plants and is able to diffuse readily, via intercellular spaces, throughout the entire plant body In 1934, Gane identified that plants could synthesise ethylene and in 1935 Crocker proposed ethylene to be the hormone responsible for fruit ripening and senescence of vegetative tissues. Apples and pears are examples of fruit that produce ethylene with ripening. Ethylene is responsible for the changes in texture, softening, color, and other processes involved in ripenining.
ROLE OF ETHYLENE Fruit ripening Under natural conditions, fruits undergo a series of changes, including changes in colour, declines in organic acid content and increases in sugar content. In many fruits, these metabolic processes often coincide with a period of increased respiration, the respiratory climacteric . During the climacteric there is also a dramatic increase in ethylene production. Ethylene can initiate the climacteric in a number of fruits and is used commercially to ripen tomatoes, avocados, melons, kiwi fruit and bananas.
Shoot Growth Applied ethylene has the capacity to influence shoot growth. Application of ethylene to dark-grown seedlings can cause reduced elongation of the stem, bending of the stem and swelling of the epicotyl or hypocotyl. Ethylene treatment of seedlings promotes hook closure and stem thickening rather than elongation. These etiolated pea seedlings were treated with 0, 0.1 and 1 ppm ethylene (left to right)
Flowering The ability of ethylene to affect flowering in pineapples has important commercial applications . Growth effects Inhibits logitudinal but promotes horizontal growth. Breaks dormancy
REFERENCES Chawla H.S(2009 ) , Introduction to plant biotechnology(3rd edition), Science publishers, 22- 23 Edwin F. George, Edwin F. George, Michael A. Hall, Geert-Jan De Klerk (2007) - Plant Propagation by Tissue Culture.The Background, Volume 1,Springer,175-282
