PLANT GROWTH REGULATORS
GROWTH PROMOTERS GROWTH INHIBITORS
AUXINS GIBBERELLINS CYTOKININS EHTYLENE ABA
DERIVATIVES Indole compound Terpenes Adenine derivatives Gaseous Carotenoids
(N⁶ furfurylamino
purine, kinetin)
DISCOVERY (Observation) (Observation) (Observation) (Confirmed) (Reported)
Charles Darwin & Kurosawa (1926) F.S SKOOG & CO H.H cousin (1910) In 1960’s
Francis Darwin Bakane (foolish WORKERS Ripe orange Independent
Canary grass seedlings) by pathogen ‐ Tobbaco callus grows to researches
(Isolation) Gibberellic fujikuroi fast by auxin & any one Unripe banana reported 3
First isolated from First discovered and of vascular tissue or different
human urine extensively studied GA‐3 yeast extract or coconut inhibitors
F.W.Went (Isolation) milk or DNA Inhibitor‐B
Coleoptile of Oat YABUTA SUMIKI (Isolation) ,Abscission II and
seedlings [NOT IN NCERT} Miller et al (1955) Dormin
Kinetin (crystallization) All are same and
from herring sperm DNA now named
Cytokinesis promoting Abscisic acid
active substances (ABA)
ZEATIN
from corn kernels
coconut milk
SITE OF Root apex & Shoot apex Root apex & Shoot apex, root apex developing Senescent parts & Ripening
SYNTHESIS and then migrate young leaves and seed shoot buds young fruits fruits
embryos [NOT IN
NCERT]
TYPES 1. Natural More than 100 KINETIN NA NA
i. IAA gibberellins reported ZEATIN
ii. IBA from widely different
2. Synthetic organisms such as fungi
i. NAA and higher plants. They
ii. 2,4‐D are denoted as GA1 ,
GA2 , GA3 and so on
EFFECTS Used extensively in Increase in length of axis Produce new leaves Most widely used PGR in General plant
agricultural and is used to increase the Chloroplasts in leaves agriculture growth inhibitor
horticultural practices length of grapes stalks Lateral shoot growth Horizontal growth of seedlings. of plant
Initiate rooting in stem Cause fruits like apple to and adventitious shoot Swelling of the axis metabolism.
cuttings elongate and improve its formation. Apical hook formation in dicot Inhibits seed
Promote flowering e.g. in shape Overcome the apical seedlings. germination.
pineapples Delay senescence. Thus, dominance. Promotes senescence and Stress hormone
prevent fruit and leaf the fruits can be left on Delay of leaf senescence abscission of plant organs by stimulates the
drop at early stages but the tree longer so as to by nutrient mobilisation especially of leaves and flowers. closure of
promote the abscission extend the market period Fruit ripening by (rising stomata and
of older mature leaves GA3 is used to speed up respiratory rate) respiratory increases the
and fruits the malting process in climactic. tolerance of
apical dominance brewing industry. Breaks seed and bud dormancy plants to various
Removal of shoot tips Increases the length of Initiates germination in Peanut
kinds of stresses.
(decapitation) usually sugarcane stem, seeds, sprouting of Potato Seed
results in the growth of increasing the yield by 20 tubers. development,
lateral buds hence widely tonnes per acre maturation and
Promotes rapid
applied in tea Early seed production in internode/petiole elongation in
dormancy. to
plantations, hedge‐ juvenile conifers by withstand
deep water Rice plants by
making. hastening the maturity desiccation and
helping leaves/ upper parts of
Parthenocarpy, e.g., in period. the shoot to remain above water.
other factors
tomatoes Promotes bolting unfavourable for
Promotes root growth and root growth.
Herbicidal ‐ . 2, 4‐D, (internode elongation hair formation.
widely used to kill dicot just prior to flowering) in In most
Initiate flowering and for situations, ABA
weeds, does not affect beet, cabbages and many synchronising fruit‐set in
mature monocot plants plants with rosette habit acts as an
Pineapples. antagonist to
Induces flowering in Mango GAs.
Ethephon (aqueous solution)
hastens fruit ripening in
Tomatoes and Apples
Accelerates abscission in flowers
and fruits (thinning of cotton,
Cherry, Walnut).
Promotes female flowers in
Cucumbers thereby increasing
the yield.
