AP Biology February 15, 2012  Objective  Describe the effects of various hormones on plant growth  Investigate how a plant respond to different stressors  Homework  Hormones Free Response Essay

AP Biology 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 Phototropism © 2011 Pearson Education, Inc.

AP Biology  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.

AP Biology Figure 39.5 Control Light Shaded side Illuminated side Boysen-Jensen Light Darwin and Darwin Gelatin (permeable) Mica (impermeable) Tip removed Opaque cap Trans- parent cap Opaque shield over curvature RESULTS

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

AP Biology Plant hormones  Auxin  cytokinins  gibberellins  abscisic acid  ethylene  and more…

AP Biology Auxin (IAA)  Effects  controls cell division & differentiation  phototropism  growth towards light  asymmetrical distribution of auxin  cells on darker side elongate faster than cells on brighter side  apical dominance

AP Biology 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.

AP Biology Gibberellins  Family of hormones  over 100 different gibberellins identified  Effects  stem elongation  fruit growth  seed germination plump grapes in grocery stores have been treated with gibberellin hormones while on the vine

AP Biology Abscisic acid (ABA)  Effects  Closure of stomata during H 2 O 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  light, temperature, moisture

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

AP Biology Fruit ripening  Adaptation  hard, tart fruit protects developing seed from herbivores  ripe, sweet, soft fruit attracts animals to disperse seed  Mechanism  triggers ripening process  breakdown of cell wall  softening  conversion of starch to sugar  sweetening  positive feedback system  ethylene triggers ripening  ripening stimulates more ethylene production

AP Biology 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.

AP Biology 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

AP Biology Learning Check  Identify the function and location of the following plant hormones  Auxin  Cytokinins  Gibberellins  Abscisic acid  Ethylene

AP Biology Plant Stress  Stress response 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

AP Biology Don’t take this lying down… Ask Questions!!