Understanding Plant Hormones and Their Role in Growth and Development

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Chemicals that are made in one part of an
organism, but affect another part of the
organism
Allows a plant to respond to some stimulus in
the environment
Allows it to bloom at an appropriate time
Allows it to grow toward a light source
Allows a seed to germinate at the appropriate
time
Etc.,
 
Hormones-Organic compounds that occur in
low amount and act as chemical messengers.
Usually synthesized in one part of the plant
and transported to the another part where it
causes a physiological reaction
They influence cell differentiation, cell
elongation and cell division
 
auxin
gibberellins
abscisic acid
 
Produced in the terminal buds of the
stems(apical meristem)
Moves downwards in the phloem, from the
growing point to the rest of the plant
Small amounts produced in growth points of
roots, most produced in growth point of
stem.
 
 Stimulate:
Cell division
Cell elongation (growth in stem
length)(
The development of fruit
The abscission of leaves and
fruit
The development of
adventitious root in stem
cuttings
Tropic movement in stem and
roots
apical dominance it suppress
the growth of the lateral buds.
 
 
Gibberellins are one of the largest groups of
plant hormones and occur mainly in the
terminal buds of stems and roots, in young
leaves and in embryos
 
Stimulate:
Stem elongation
Root growth
The germination of seeds
Promotes flowering
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It is a growth inhibitor that counteract the
actions of auxins.
It occurs in leaves, stems and unripe fruit
 
Accelerate abscission in leaves and fruit. ABA
is produced in ripe fruit and induced fruit fall.
ABA stimulates the closing of stomata in most
plant species. Its synthesis is stimulated by
water deficiency (water stress) Abscisic acid;
Causes dormancy in apical and lateral buds in
winter.
Controls seed dormancy by inhibiting
germination
Causes the closing of stomata when the plant
wilts
 
 
Is a growth movement of part of the a plant in
response to an external onE sided stimulus.
Direction of the growth is determined by the
direction of the stimulus
A growth movement in the direction of the
stimulus is a positive reaction
A growth movement away for the stimulus  is a
negative reaction
Tropism takes place as a result of the unequal
distribution of auxins in the plant. Certain plant
part grow faster than others
High auxin concentration in the stems stimulates growth
High auxin concentration in the roots inhibits growth.
 
 
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Movement of plant toward a light stimulus
 
 
 
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GEOTROPISM
 
Experiment  to illustrate geotropism
 
Roots growth downwards
 
Clinostat turned –roots growth striat
Geotropism in nature
 
Apical domination is a phenomenon where
the terminal bud suppress the development
of lateral buds
 
The apical bud( tip of the main shoot) of most
plants grow more vigorously/faster then the
lateral buds( tips of the side branches) below
it
The plant therefore, grows vertically and the
growth of the side branches is inhibited
This is called Apical dominance.
It is caused by the production of auxins in the
apical buds.
These auxins move down to the lateral buds
and inhibits there growth
 
When the apical bud is removed, the
controlling influence of the apical bud over
the growth of the lateral buds is removed
The lateral branches grow out
 
 
Plant hormones are used extensively in the
production of food crops.
It Includes the following:
Root formation from cuttings
Production of seedless fruit
Ripening of fruit
Prevention of premature abscission of fruit
Increase in fruit size
Stimulation of germination
Weed control
 
Gibberellin induces growth in grapes. The
bunch on the left is an untreated control. The
bunch on the right was sprayed with GA
3
during fruit development.
 
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Use of Auxins
 
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Auxins accelerate the metabolism of
broad-leaved dicotyledonous weed
and therefore stimulate growth These
weeds grow so fast that their water
absorption and food production are
insufficient. The plants weaken and
die.
 
Application of Gibberellins cause cell elongation
 
 
In this experiment carried out on
germinating barley seeds, the
results showed that the release
of gibberellin from the embryo,
triggers the germination
 
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Plants respond to the direction
and amount of light they
receive. The seedlings on the
left grew toward the light it
received on only one side. The
plant in the center received no
light. The plant on the right was
grown in normal, all-around light
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Plant hormones are essential chemicals that enable plants to respond to environmental stimuli, regulate growth processes like cell division and elongation, and control key developmental stages such as flowering and fruit development. Key hormones include auxin, gibberellins, and abscisic acid, each with specific functions and sources within the plant. They play vital roles in stem elongation, root growth, seed germination, and fruit development. Understanding these hormones is crucial for optimizing plant growth and development in agriculture and horticulture practices.


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  1. Plant Hormones - Responding to Stimuli

  2. Chemicals that are made in one part of an organism, but affect another part of the organism Allows a plant to respond to some stimulus in the environment Allows it to bloom at an appropriate time Allows it to grow toward a light source Allows a seed to germinate at the appropriate time Etc.,

  3. Hormones-Organic compounds that occur in low amount and act as chemical messengers. Usually synthesized in one part of the plant and transported to the another part where it causes a physiological reaction They influence cell differentiation, cell elongation and cell division

  4. auxin gibberellins abscisic acid

  5. Produced in the terminal buds of the stems(apical meristem) Moves downwards in the phloem, from the growing point to the rest of the plant Small amounts produced in growth points of roots, most produced in growth point of stem.

  6. Stimulate: Cell division Cell elongation (growth in stem length)( The development of fruit The abscission of leaves and fruit The development of adventitious root in stem cuttings Tropic movement in stem and roots apical dominance it suppress the growth of the lateral buds.

  7. Gibberellins are one of the largest groups of plant hormones and occur mainly in the terminal buds of stems and roots, in young leaves and in embryos

  8. Stimulate: Stem elongation Root growth The germination of seeds Promotes flowering Stimulate: plump grapes in grocery stores have been treated with gibberellin hormones while on the vine

  9. It is a growth inhibitor that counteract the actions of auxins. It occurs in leaves, stems and unripe fruit

  10. Accelerate abscission in leaves and fruit. ABA is produced in ripe fruit and induced fruit fall. ABA stimulates the closing of stomata in most plant species. Its synthesis is stimulated by water deficiency (water stress) Abscisic acid; Causes dormancy in apical and lateral buds in winter. Controls seed dormancy by inhibiting germination Causes the closing of stomata when the plant wilts

  11. Is a growth movement of part of the a plant in response to an external onE sided stimulus. Direction of the growth is determined by the direction of the stimulus A growth movement in the direction of the stimulus is a positive reaction A growth movement away for the stimulus is a negative reaction Tropism takes place as a result of the unequal distribution of auxins in the plant. Certain plant part grow faster than others High auxin concentration in the stems stimulates growth High auxin concentration in the roots inhibits growth.

  12. Phototropism Movement of plant toward a light stimulus

  13. Auxin associated with phototropism - early experiments demonstrate tip as receptor.

  14. Geotropism

  15. GEOTROPISM

  16. Experiment to illustrate geotropism Roots growth downwards

  17. Clinostat turned roots growth striat

  18. Geotropism in nature

  19. Apical domination is a phenomenon where the terminal bud suppress the development of lateral buds

  20. The apical bud( tip of the main shoot) of most plants grow more vigorously/faster then the lateral buds( tips of the side branches) below it The plant therefore, grows vertically and the growth of the side branches is inhibited This is called Apical dominance. It is caused by the production of auxins in the apical buds. These auxins move down to the lateral buds and inhibits there growth

  21. When the apical bud is removed, the controlling influence of the apical bud over the growth of the lateral buds is removed The lateral branches grow out

  22. Plant hormones are used extensively in the production of food crops. It Includes the following: Root formation from cuttings Production of seedless fruit Ripening of fruit Prevention of premature abscission of fruit Increase in fruit size Stimulation of germination Weed control

  23. Use of gibberellins 2 Gibberellin induces growth in grapes. The bunch on the left is an untreated control. The bunch on the right was sprayed with GA3 during fruit development.

  24. Use of Auxins

  25. Auxins as herbicides Auxins accelerate the metabolism of broad-leaved dicotyledonous weed and therefore stimulate growth These weeds grow so fast that their water absorption and food production are insufficient. The plants weaken and die. http://plantandsoil.unl.edu/croptechnology2005/UserFiles/Image/siteImages/GrowthRegSMALL.jpg http://plantandsoil.unl.edu/croptechnology2005/UserFiles/Image/siteImages/GrowthRegulatorsbinjurySMALL.jpg

  26. Application of Gibberellins cause cell elongation

  27. Use of gibberellins to http://www.biyolojiegitim.yyu.edu.tr/k/Gib/images/Gibberellin_jpg.jpg stimulate seed germination In this experiment carried out on germinating barley seeds, the results showed that the release of gibberellin from the embryo, triggers the germination

  28. Plants respond to the direction and amount receive. The seedlings on the left grew toward the light it received on only one side. The plant in the center received no light. The plant on the right was grown in normal, all-around light of light they

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