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Charles and Francis Darwin (1880)

Plant Hormones. Charles and Francis Darwin (1880) There is an ‘influence’ which moves from the tip to the cells below. Went purified the ‘influence’ and identified Indole-3-acetic acid (IAA). Very small molecules – can move across cell walls.

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Charles and Francis Darwin (1880)

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  1. Plant Hormones Charles and Francis Darwin (1880) There is an ‘influence’ which moves from the tip to the cells below.

  2. Went purified the ‘influence’ and identified Indole-3-acetic acid (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

  3. PLANT RESPONSES CYTOPLASM CELL WALL 3 Response   1 Reception 2 Transduction Activation of cellular responses Relay molecules Receptor Hormone or environmental stimulus Plasma membrane Figure 39.3

  4. 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

  5. Plant Hormones (growth regulators) • Auxin or IAA • Gibberellins • Cytokinins • Ethene • Abscisic acid

  6. Auxin

  7. Meristem Auxins are produced in meristematic tissue Growing point – part of plant which grows most

  8. Auxin will migrate to the dark side of an illuminated stem

  9. Geotropism Movement of dense molecules in sensitive cells. AMYLOPLASTS (statoliths - starch granules) Cause redistribution of auxin to lower parts Auxinsact as inhibitors in roots

  10. Cytokinins • Often have opposite effect to auxin • Stimulate lateral buds  bushiness

  11. Giberellins • Produced at growing tips  longer internodes • promote seed germination • stem thickening

  12. Other Hormones • Ethene ripens fruit • Abscisic acid (ABA) inhibits auxins, cytokinins and giberellin

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