3. Plant Hormones
• Chemicals that regulate plant growth
• Signal molecules produced within the plant,
and occur in extremely low concentrations.
• Chemical messengers that affect a plant's
ability to respond to its environment.
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4. General Plant Hormones
There are some plant hormone which are
described below:
• Auxins
• Gibberellins
• Cytokinins
• Ethylene
• Abscisic Acid
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5. Auxins
• First of the major plant hormones to be discovered.
• Indole-3-acetic acid (IAA) is the most common,
naturally-occurring, plant hormone of the auxin class.
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6. Functions of Auxins
• Frits Went (1926) determined auxin
enhanced cell elongation and Stem
elongation.
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7. Functions of Auxins
• Auxins also influences root formations.
• Responsible for apical dominance and
phototropism.
• Promotes xylem differentiation.
• Retards leaf abscission.
• Promotes fruit growth.
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8. Gibberellin
• Produce in young, developing shoots and seeds
• Gibberellin have some known actions in the development of:
• Cell division
• Cell elongation
• Stimulate seed germination
• Stimulate flowering
• Stimulate fruit development
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9. Commercial use of GA
Thompson seedless grapes (Vitis (Vitaceae fami
Without GA With GA
Larger fruits that are easier to clean are attractive in markets
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10. Cytokinins
• Produce in primarily root tips
• Cytokinins have some known actions in the
process of:
• Cell division (cytokinesis)
• Tissue culture
• Delay leaf senescence
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11. Cytokinin delays leaf senescence (ageing
and reabsorption of aged organs)
Transgenic Untreated
Genetic
modification
to increase
Cytokinin
biosynthesis
Nicotiana (Solanaceae family)
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12. Ethylene
• Produce in most tissues under stress, senescence, or
ripening
• Ethylene have some known actions in the development
of:
• Fruit ripening
• Leaf and flower senescence
• Leaf and fruit abscission (controlled separation of plant
part from the main body)
• Floral sex determination in monoecious species, promote
female
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13. Experimenting with plant response to ethylene
commercial uses
Mutated ethylene receptor Normal ethylene receptor levels
Both are 100 days after picking
Lycopersicon (Solanaceae family)
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14. Abscisic Acid (ABA)
• Abscisic Acid Produce in:
• Mature leaves, especially under stress
• Roots, then transported to shoots
• Abscisic Acid have some known actions that is:
1. Stress response
2. Stimulate stomatal closure
3. Inhibit premature germination of seeds
4. Embryogenesis
5. Seed dormancy maintenance
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15. ABA induces stomatal closure
a simplified diagram
Solutes (e.g. potassium and
chloride ions) accumulate in guard
cells causing water to accumulate in
guard cells, making them turgid
ABA is one signal that causes guard cells
to release solutes and thus release
water, making them flaccid and closing
the stoma (pore) between them
Guard cell response to ABA is one topic of research in the Outlaw lab at FSU
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