charles and francis darwin (1880) there is an ‘influence’ which moves from the tip to the cells...
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Charles and Francis Darwin (1880)There is an ‘influence’ which moves from the tip to the cells below.
Plant Hormones
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Went purified the ‘influence’and identified Indole-3-aceticacid (IAA)
Very small molecules – can move across cell walls
Hormone = compound produced by one part of an organism that is transported to other parts where it triggers a response in target cells
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PLANT RESPONSES
CELLWALL
CYTOPLASM
1 Reception 2 Transduction 3 Response
Receptor
Relay molecules
Activationof cellularresponses
Hormone orenvironmentalstimulus
Plasma membrane
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Functions of Hormones• Coordinate growth and development by
affecting division, elongation and differentiation of cells
• Regulate responses to environmental stimuli
• Varying concentrations affect target cells differently; and different target cells are affected differently
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Plant Hormones (growth regulators)
Auxin or IAA
Gibberellins
Cytokinins
Ethene
Abscisic acid
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Auxin
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Meristem
Growing point – part of plant which grows most
Auxins are produced in meristematic tissue
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Auxin will migrate to the dark side of an illuminated stem
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Geotropism
Movement of dense molecules in sensitive
cells.
AMYLOPLASTS (statoliths - starch granules)
Cause redistribution of auxin to lower parts
Auxins act as inhibitors in roots
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Cytokinins• Often have opposite effect to auxin• Stimulate lateral buds bushiness
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Giberellins• Produced at growing tips longer internodes• promote seed germination• stem thickening
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Other Hormones• Ethene ripens fruit• Abscisic acid (ABA) inhibits auxins,
cytokinins and giberellin
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