Role of plant growth regulators
AUXIN:
Roles
Auxin is a growth promoter. The naturally produced auxins is Indole-3-Acetic Acid (IAA). They are
also produced by chemical synthesis, which show same physiological responses like Auxin.
Site of Auxin synthesis: Auxins are synthesized in stem tips and in young tissues and move mainly
down stem (Basipetal movement) i.e., from shoot tip to root.
1. Cell division and enlargement: IAA + GA, example - cambial growth in diameter.
2. Tissue culture: Shoot multiplications (IBA and BAP), callus growth (2, 4-D), root multiplication
IAA and IBA (1-2 mg).
3. Breaking dormancy and apical dominance (inhibition of lateral buds): NAA
4. Shortening internodes: Apple trees (NAA) dwarf branch fruit.
5. Rooting of cutting: (10-1000 ppm-NAA, IAA, Phenyl acetic acid)
6. Prevent lodging: NAA develop woody and erect stem.
7. Prevent abscission: premature leaf, fruit and flower fall (NAA, IAA and 2,4-D).
8. Parthenocarpic fruit: Grapes, Banana and Orange (IAA).
9. Flower initiations: Pineapple uniform flowering and fruit ripening (NAA) and delay flowering (2, 4-
D).
10. Weed eradication: 2, 4-D
GIBBERELLINS:
It is the active principle isolated from the soil borne fungus Gibberella fujikuroi.
The concentration of GA3 is usually the highest in immature seeds, reaching up to 18 mg/kg fresh
weight in Phaseolus species, but it decreases rapidly as the seeds mature.
In general, roots contain higher amounts of GA3 than shoots. Gibberellins have also been found
effective in overcoming both kinds of dormancy in buds as well as seeds.
Role of Gibberellins:
1. GA: Synthesis in leaf and induce shoot elongation (IAA + GA3), by effecting cell elongation or cell
division or both.
, 2. Enhance metabolic activity: Mobilization of reserved food material, promote growth and height,
increase root activity and kinetin production in root- translocate to growing bud.
3. Shoot elongation: GA3 spray increases height of seedlings.
4. Delay senescence: Increase photosynthetic and protein synthesis so decrease abscission.
5. Increase cambial growth and differentiation:
6. Induce flower and fruit set (IAA+GA3).
7. Dwarf plant (genetically) to normal height: GA3.
8. Promote flowering in Long Day Plants: Substitute for long day condition and cold treatment
(vernalization).
9. Induction of parthenocarpy in grapes: Three physiological events: Rachis cell elongation, flower
thinning and berry enlargement.
10. Breaking dormancy and leaf expansion
CYTOKININS:
First endogenous cytokinin was isolated from maize kernels named as zeatin.
Germinating seeds, roots, sap streams, developing fruits and tumor tissues are rich in cytokinins.
Cytokinins imbibed seeds germinate better in dark than unimbibed lettuce seeds.
Synthetic cytokinins are: Kinetin, Benzyladenine and Ethoxy ethyladenine.
Role of cytokinin:
1. Cell division, elongation and enlargement.
2. Tissue culture morphogenesis.
3. Induction of flowering and fruit development.
4. Parthenocarpy.
5. Apical dominance overcoming.
6. Breaking dormancy.
7. Delay senescence.
8. Improves N2 metabolism.
ETHYLENE:
AUXIN:
Roles
Auxin is a growth promoter. The naturally produced auxins is Indole-3-Acetic Acid (IAA). They are
also produced by chemical synthesis, which show same physiological responses like Auxin.
Site of Auxin synthesis: Auxins are synthesized in stem tips and in young tissues and move mainly
down stem (Basipetal movement) i.e., from shoot tip to root.
1. Cell division and enlargement: IAA + GA, example - cambial growth in diameter.
2. Tissue culture: Shoot multiplications (IBA and BAP), callus growth (2, 4-D), root multiplication
IAA and IBA (1-2 mg).
3. Breaking dormancy and apical dominance (inhibition of lateral buds): NAA
4. Shortening internodes: Apple trees (NAA) dwarf branch fruit.
5. Rooting of cutting: (10-1000 ppm-NAA, IAA, Phenyl acetic acid)
6. Prevent lodging: NAA develop woody and erect stem.
7. Prevent abscission: premature leaf, fruit and flower fall (NAA, IAA and 2,4-D).
8. Parthenocarpic fruit: Grapes, Banana and Orange (IAA).
9. Flower initiations: Pineapple uniform flowering and fruit ripening (NAA) and delay flowering (2, 4-
D).
10. Weed eradication: 2, 4-D
GIBBERELLINS:
It is the active principle isolated from the soil borne fungus Gibberella fujikuroi.
The concentration of GA3 is usually the highest in immature seeds, reaching up to 18 mg/kg fresh
weight in Phaseolus species, but it decreases rapidly as the seeds mature.
In general, roots contain higher amounts of GA3 than shoots. Gibberellins have also been found
effective in overcoming both kinds of dormancy in buds as well as seeds.
Role of Gibberellins:
1. GA: Synthesis in leaf and induce shoot elongation (IAA + GA3), by effecting cell elongation or cell
division or both.
, 2. Enhance metabolic activity: Mobilization of reserved food material, promote growth and height,
increase root activity and kinetin production in root- translocate to growing bud.
3. Shoot elongation: GA3 spray increases height of seedlings.
4. Delay senescence: Increase photosynthetic and protein synthesis so decrease abscission.
5. Increase cambial growth and differentiation:
6. Induce flower and fruit set (IAA+GA3).
7. Dwarf plant (genetically) to normal height: GA3.
8. Promote flowering in Long Day Plants: Substitute for long day condition and cold treatment
(vernalization).
9. Induction of parthenocarpy in grapes: Three physiological events: Rachis cell elongation, flower
thinning and berry enlargement.
10. Breaking dormancy and leaf expansion
CYTOKININS:
First endogenous cytokinin was isolated from maize kernels named as zeatin.
Germinating seeds, roots, sap streams, developing fruits and tumor tissues are rich in cytokinins.
Cytokinins imbibed seeds germinate better in dark than unimbibed lettuce seeds.
Synthetic cytokinins are: Kinetin, Benzyladenine and Ethoxy ethyladenine.
Role of cytokinin:
1. Cell division, elongation and enlargement.
2. Tissue culture morphogenesis.
3. Induction of flowering and fruit development.
4. Parthenocarpy.
5. Apical dominance overcoming.
6. Breaking dormancy.
7. Delay senescence.
8. Improves N2 metabolism.
ETHYLENE:
