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Plant Hormones and Response to Stimuli

Plant Hormones and Response to Stimuli. What are hormones and what do they do?. Regulate transcription by binding transcription factors to DNA: Initiated by hormones through second messengers .

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Plant Hormones and Response to Stimuli

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  1. Plant Hormones and Response to Stimuli What are hormones and what do they do?

  2. Regulate transcription by binding transcription factors to DNA: Initiated by hormones through second messengers. • Two second messenger pathways exist: One uses cyclic GMP or cGMP, the other uses Ca+Calmodulin to activate transcription. G-protein and protein kinases also involved. • The light sensitive receptor phytochrome may initiate the greening response. • Hormones are produced in one part of the body and have effects elsewhere in the body. • Very small amounts are required. • In plants, the response is often governed by the interaction of two or more hormones

  3. Early Experiments of Phototropism

  4. F. W. Went, 1926 Investigates Phototropism Agar block collected auxin, or Indole Acetic Acid (IAA) In the dark, off-center block caused grass coleoptile to bend. Proves chemical produced by the tip affects bending.

  5. Acid Growth Hypothesis

  6. Auxins (IAA)

  7. Gibberellins(Gibberellic Acids)

  8. Effect of Gibberellin Treatment on Seedless Grapes

  9. Ethylene Gas

  10. Ethylene Induces the Triple Response of Germinating Seedlings to Circumvent Obstacles in Soil

  11. Cytokinins

  12. Abscisic Acid (ABA) ABA is a growth inhibitor. Maintains dormancy in seeds. Works against many other growth hormones. Enables plants to respond to drought.

  13. Plant Responses to Stimuli • Phototropism – Response to light due to auxin: the higher auxin in the shady side of the stem, the more bending toward the light occurs. • Gravitropism (geotropism) – Response to gravity: both auxin and gibberellin are involved. • Thigmotropism – Response to touch in climbing vines.

  14. Action Spectrum For Blue-Stimulated Phototropism

  15. Photoperiodism A flash of light during the night resets the biological clock.

  16. Red light shortens the night length, and far-red restores the night length. The last flash determines the night length.

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