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Summary PLANT HORMONES
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PLANT HORMONES summary
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PLANT HORMONES- plants are living organisms; must grow and develop
- growth: increase in size
- development: changes during growth
GROWTH and DEVELOPMENT controlled by:
✴ genes
✴hormones
CHARACTERISTICS OF PLANT HORMONES:
1. organic chemical messengers
2. produced in one part of plant and transported in the phloem to another part
3. hormone affects growth and development of part called target organ
4. hormones work in small amounts
5. reaction to hormones is usually slow
In order to survive plants must grow in response to external stimuli.
Tropisms: growth responses to directional stimuli that are controlled by hormones.
PLANT HORMONES: 3 main groups
- GIBBERELLINS: produced in terminal buds of stem and roots, young leaves and
embryos
Function:
- stimulate stem elongation (plants grow taller)
- promote flowering
- stimulate germination of seeds
- encourage fruit development
- ABSCISSIC ACID: growth inhibiter and counteracts functioning of auxins. Helps
plant cope in stressful situations
Functions:
- slows growth down (causes dormancy of terminal buds and lateral buds in winter)
- causes dormancy of seeds (inhibits germination)
- promotes abscission of leaves and fruit (grow old and fall off)
- AUXINS: produced in apical regions of stems and roots. High concentration of
auxins in stems stimulates growth and high concentration of auxins in roots inhibits
growth.
, Functions:
- stimulate cell elongation
- stimulate development of fruit (seedless)
- control abscission of leaves and fruit
- stimulate development of adventitious roots in stem cuttings
- cause tropisims in stems and roots
- INHIBITS GROWTH OF LATERAL BRANCHES-APICAL DOMINANCE
Auxin produced at tip-high
concentration
Inhibit development
of lateral branches
Auxin concentration low
therefore lateral branches
grow well
APICAL DOMINANCE
THE USE OF PLANT HORMONES IN AGRICULTURE:
✦ root formation in cuttings
✦ production of seedless fruits
✦ ripening of fruits
✦ prevention of premature abscission of fruit
✦ increase size of fruits
✦ WEED CONTROL
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