INTRODUCTION
• The term plant growth regulators is relatively new in using
earlier these were mentioned as
hormones .which to stimulate
• Thimonn(1948)suggested
the term phytohormone in
place of hormone of plants
• he defined phytohormones
as the organic substances
which are produced
naturally in plants.
TYPES OF PGR'S
●PGRS are mainly classified into
5
types : ▪ Auxin
▪ Gibberellins
▪ Cytokinins
▪ Abscisic acid
▪ Ethylene
AUXIN
• The existence of the Auxin was proposed by
Charles darwin(1880).
• In 1920 WENT named scientist performed d
"AVENACURVATURE TEST .
• Auxin is synthesized in shoot tip region particularly
in oung leaves ,developing embryo and in
developing fruits
• The synthesis begins with the Synthesis of amino
acid tryptophan. Tryptophan is known as precursor
of IAA
• Auxin have polar movement ie.apex to downward
ROLE OF AUXIN:-
•APICAL DOMINANCE:Auxin inhibits lateral
bud formation when apical bud is
removed ,lateral buds begins to sprout. Such
phenomenon is known as"apical dominance
• CELL DIVISION &ENLARGEMENT:- are
promoted by
Auxin in shoots &coleoptiles .making the plant wall
more flexible ,which allows the plant to grow
upwards
• SHOOT&ROOT GROWTH:-Auxin increases shoot
growth at relatively higher concentration and root
growth ar a very low concentration
• ABSCISSION:- Auxin promotes the abscisson of
order leaves and fruits
• PARTHENOCARPY:- It accelerates cell
enlargement and this swelling of the ovary ,leading
to development of fruits
GIBBERELLINS
• Gibberellins was discovered by
kurosava
(1926)
• It was first extracted from fungus
Giberalla fujikuroi (Fusarium
moniliforme)
• Yabuta, hayashi and kannabe first
isolated the active principal from the
fungus which was called Gibberellin
• West and phinney (1956) discovered
GA3 as a natural product of higher
ROLE OF GIBBERELLINS :-
•Prevention of genetical
dwarfism :Genetic dwarfism in plants may be
due to gene mutation. The mutation causes a
block in thd Gibberellins synthesis. When
Gibberellins are applied these plants elongate
in comparison to their normal counterpart
•Bolting & flowering:- plants which need a
cold treatment to bolt and flower ,can be
brought into flowering following Gibberellins
treatment
•Light inhibited stem growth:- inhibition
can overcome by applying of Gibberellins the
plasticitynof young cell walls increases
•Parthenocarpy:Gibberellins have been found
very reliable in producing parthenocarpy
Gibberellin have induced parthenocarpy in
pome &stone fruits
•Germination: treatment of seedwith
Gibberellins stimulates the activity of enzymes
analysis
CYTOKININ :-
• Cytokinins are class of plant hormones
that play a crucial role in regulating cell
division , growth, and development
• In the 1950s ,Cytokinins were initially
identified as substances that promote
cell division in plant tissues
• They primarily synthesized in the roots
and transported to other parts of the
plant
• Cytokinin also known as phytokiman
ROLE OF CYTOKININ:-
•Cell division:Cytokinin in cojugation with IAA
accounts to cell division . In order for cell
division to occur ,an ordered sequence of DNA
synthesis, mitosis and Cytokinesis must take
place
•Cell &organ enlargement:cytokinin induces
cell enlargement. It is stimulated by water
uptake. Cytokinin stimulates cotyledon
enlargement by their action on physiological
processes
•Seed germination:the germination of lettuce
seed is stimulated by red light . If it's seeds
imbibe a solution of kinetin or other cytokinin
germination is higher than the dark grown
control
•Bud development &shoot growth: kinetic
potentially Involved in regulating shoot
initiation and also apical dominance ,the
apical suppresses the growth of lateral bud
•Root initiation and growth:cytokinin is able
both to inhibit root initiation and development .
ETHYLENE
•Ethylene is the only gaseous hormone
which stimulates growth
•Gane (1934) established that Ethylene
was natural product of ripening fruit
•Evidence for Ethylene production
appeared from leaves, flowers,seeds,and
roots
•Ethylene has the simplest chemical
structure (CH2=CH2) and is synthesized
from methionine β-alanine or isoamyl
alcohol
ROLE OF ETHYLENE:-
•FRUIT RIPENING:In most fruits The rate of
respiration undergoes a sharprise and the
end of ripening. this phenomenon is termed
as climacteric
•SEEDLING GROWTH &EMERGENCE:
upon type of seed the mode of seedlings
growth in the soil and during emergence is
particularly important
•LEAF ABSCISSION:-The abscisson of the
leaf is accomplished through the formation of
parenchyma cell layers
ABSCISIC ACID:-
•In 1961 ,Liu and carns isolated a
substances from cotton fruit which
stimulates the abscisson of debladed
cotton petioles
•They called this substances abscisin -
I .but the structure of this substances
was not determined
•Its detection led to the discovery of
another substances, which ohkuma and
colleagues isolated from young cotton
fruit and termed it as abscisin-II
ROLE OF ABSCISIC ACID:-
• Abscisson:As ABA was isolated as an
Abscisson accelerating substances so it has been
firmly belived that ABA has Abscisic effect
• Dormancy: Involvement of ABA in the
induction and maintenance of dormancy was
based on the observation of high ABA content in
potato tubers and resting bud of deciduous
tree .when the plants face wliting ,large amount
of ABA is synthesized in the leaves.
• Seed development and germination : ABA
builds up in embryo of developing seeds .it has
been observed that ABA in developing ovules ,
ihibits the formation of germination enzymes in
the emryo.
• Stomach closing: ABA is well known for it's
role in stomatal closing. It inhibits potassium
uptake by the guard cells .it accounts for the
loss of turgidity of guard cell
• Helps during water stress : ABA
accumulates in water stressed mesophytic
plants and it starts decreasing when the plant
is no ponger stresss.it closes the stomata and
maintains the very existence
of plants under water stress
