Objective Describe the effects of various hormones on plant growth



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February 15, 2012

  • Objective
  • Homework
    • Hormones Free Response Essay

The Discovery of Plant Hormones

  • Any response resulting in curvature of organs toward or away from a stimulus is called a tropism
  • In the late 1800s, Charles Darwin and his son Francis conducted experiments on phototropism, a plant’s response to light
  • They observed that a grass seedling could bend toward light only if the tip of the coleoptile was present
  • Phototropism

They postulated that a signal was transmitted from the tip to the elongating region

  • They postulated that a signal was transmitted from the tip to the elongating region
  • In 1913, Peter Boysen-Jensen demonstrated that the signal was a mobile chemical substance
  • How would they design their experiments to test these hypothesis?
  • © 2011 Pearson Education, Inc.

Figure 39.5

  • Control
  • Light
  • Shaded side
  • Illuminated side
  • Boysen-Jensen
  • Light
  • Light
  • Gelatin (permeable)
  • Mica (impermeable)
  • Tip removed
  • Opaque cap
  • Trans- parent cap
  • Opaque shield over curvature
  • RESULTS

In 1926, Frits Went extracted the chemical messenger for phototropism, auxin, by modifying earlier experiments

  • In 1926, Frits Went extracted the chemical messenger for phototropism, auxin, by modifying earlier experiments
  • © 2011 Pearson Education, Inc.

Plant hormones

  • Auxin
  • cytokinins
  • gibberellins
  • abscisic acid
  • ethylene
  • and more…

Auxin (IAA)

  • Effects
    • controls cell division & differentiation
    • phototropism
    • apical dominance

Cytokinins

  • Cytokinins are so named because they stimulate cytokinesis (cell division)
  • Control of Cell Division and Differentiation
  • Cytokinins are produced in actively growing tissues such as roots, embryos, and fruits
  • Cytokinins work together with auxin to control cell division and differentiation
  • © 2011 Pearson Education, Inc.

Gibberellins

  • Family of hormones
  • Effects
    • stem elongation
    • fruit growth
    • seed germination
  • plump grapes in grocery stores have been treated with gibberellin hormones while on the vine

Abscisic acid (ABA)

  • Effects
    • Closure of stomata during H2O crisis
    • slows growth
    • seed dormancy
      • high concentrations of abscisic acid
        • germination only after ABA is inactivated or leeched out
      • survival value: seed will germinate only under optimal conditions

Ethylene

  • Hormone gas released by plant cells
  • Effects
    • fruit ripening
    • leaf drop
      • Senescence (cell death)
      • Abscission (drop)
  • One bad apple spoils the whole bunch…

Fruit ripening

  • Adaptation
    • hard, tart fruit protects developing seed from herbivores
    • ripe, sweet, soft fruit attracts animals to disperse seed
  • Mechanism
    • triggers ripening process
    • positive feedback system
      • ethylene triggers ripening
      • ripening stimulates more ethylene production

Etylene

  • Develop a hypothesis about what will happen to the bananas in the bags
  • Be sure to explain why you think it will happen that way.

Apoptosis in plants

  • What is the evolutionary advantage of loss of leaves in autumn?
  • Many events in plants involve apoptosis
    • response to hormones
      • ethylene
      • auxin
    • death of annual plant after flowering
      • senescence
    • differentiation of xylem vessels
      • loss of cytoplasm
    • shedding of autumn leaves

Learning Check

Plant Stress

  • Stress response
  • You will be divided into groups. Each group will research and explain how one of the following 1) causes stress to the plant, 2) effects a plants growth, and 3) how the plant over comes the stress
    • Gravity
    • Herbivory
    • Light
    • Salt
    • Drought
    • Mechanical stimuili
    • Flooding
    • Heat
    • Cold
    • Disease
  • 2007-2008
  • Don’t take this lying down…
  • Ask Questions!!


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