2. Vishal Agri Guru
PLANT GROWTH REGULATORS IN HORTICULTURAL CROPS
1.Plant Growth Regulators (PGR) known
as bio-stimulants or bio-inhibitors modify
physiological processes in plant.
2.These organic compounds act inside
plant cells to stimulate or inhibit
specific enzyme or enzyme systems
to regulate plant metabolism.
3.These growth regulators are naturally
produced in plants to control the growth
and other physiological functions. They
act even in very minute quantities.
6. Vishal Agri Guru
• Cell Enlargement: It stimulates cell enlargement and stem
growth.
• Cell Division: It stimulates cell division in cambium. Used in tissue
culture plant production in combination with Cytokinin.
• Vascular Tissue Differentiation: It stimulates differentiation of phloem
and xylem.
• Root Initiation: It stimulates root initiation on stem cuttings. Used in
plant propagation by tissue culture for development of roots.
• Apical Dominance: It suppresses the apical shoot growth and
promotes the growth of lateral buds.
Role of Auxins:
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• Stem growth: Gibberellic Acid (GA) causes hyper elongation of
stems by stimulating both cell division and cell elongation. This
results in taller plants.
• Bolting in long day plants: GA cause stem elongation in response
to long days.
• Induction of seed germination: GA activates germination of seeds
which otherwise require cold (stratification) or light to induce
germination.
• Enzyme production during germination: GA stimulates the
production of enzymes like amylase in germinating cereal grains.
Role of Gibberellins:
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• Stomata Closure: Water shortage brings about increase in ABA level,
leading to stomata closure as a response to water stress.
• Growth Inhibitors: ABA inhibits shoot growth but has less effect on
root growth.
• GA Counteracts: ABA counteracts the effect of gibberellins on a-
amylase synthesis in germinating cereal grains.
• Induced Dormancy: ABA affects induction or maintenance of
dormancy in seeds.
Role of Abscisic Acid (ABA):
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• Fruit Ripening: Ethylene in the form of gas helps ripens fruits under
natural conditions.
• Induction Of Femaleness: Promotes production of female flowers in
cucurbits (cucumber, squash, melon) to increase the yield.
• Flower Opening: Promotes flower initiation and controlled ripening in
pineapples.
• Leaf and Fruit Abscission: Accelerates fruit abscission for mechanical
harvesting in fruit crops such as grapes, cherries, and citrus.
Role of Ethylene:
10. Vishal Agri Guru
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