1. LECTURE PRESENTATIONS For CAMPBELL BIOLOGY, NINTH EDITION Jane B. Reece, Lisa A. Urry, Michael L. Cain, Steven A. Wasserman, Peter V. Minorsky, Robert B. Jackson © 2011 Pearson Education, Inc. Lectures by Erin Barley Kathleen Fitzpatrick Plant Responses to Internal and External Signals Chapter 39

2. Figure 39.2 (a) Before exposure to light(b) After a week’s exposure to natural daylight

3. A potato’s response to light is an example of cell-signal processing The stages are reception, transduction, and response © 2011 Pearson Education, Inc.

4. Figure 39.3 Reception CELL WALL 2 31 Transduction CYTOPLASM Response Relay proteins and second messengers Activation of cellular responses Receptor Hormone or environmental stimulus Plasma membrane

5. Reception Internal and external signals are detected by receptors, proteins that change in response to specific stimuli In de-etiolation, the receptor is a phytochrome capable of detecting light © 2011 Pearson Education, Inc.

6. Transduction Second messengers transfer and amplify signals from receptors to proteins that cause responses Two types of second messengers play an important role in de-etiolation: Ca 2+ ions and cyclic GMP (cGMP) The phytochrome receptor responds to light by –Opening Ca 2+ channels, which increases Ca 2+ levels in the cytosol –Activating an enzyme that produces cGMP © 2011 Pearson Education, Inc.

7. Figure 39.4-1 Reception 1 CYTOPLASM Plasma membrane Phytochrome Cell wall Light

8. Figure 39.4-2 Reception 2 1 Transduction CYTOPLASM Plasma membrane Phytochrome Cell wall Light cGMP Second messenger Ca 2  Ca 2  channel Protein kinase 1 Protein kinase 2

9. Figure 39.4-3 Reception 23 1 Transduction Response CYTOPLASM Plasma membrane Phytochrome Cell wall Light cGMP Second messenger Ca 2  Ca 2  channel Protein kinase 1 Protein kinase 2 Transcription factor 1 Transcription factor 2 NUCLEUS Transcription Translation De-etiolation (greening) response proteins P P

10. Response A signal transduction pathway leads to regulation of one or more cellular activities In most cases, these responses to stimulation involve increased activity of enzymes This can occur by transcriptional regulation or post-translational modification © 2011 Pearson Education, Inc.

11. Concept 39.2: Plant hormones help coordinate growth, development, and responses to stimuli Plant hormones are chemical signals that modify or control one or more specific physiological processes within a plant © 2011 Pearson Education, Inc.

12. 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 © 2011 Pearson Education, Inc.

13. 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

14. A Survey of Plant Hormones Plant hormones are produced in very low concentration, but a minute amount can greatly affect growth and development of a plant organ In general, hormones control plant growth and development by affecting the division, elongation, and differentiation of cells © 2011 Pearson Education, Inc.

15. Table 39.1

16. Auxin The term auxin refers to any chemical that promotes elongation of coleoptiles Indoleacetic acid (IAA) is a common auxin in plants; in this lecture the term auxin refers specifically to IAA Auxin is produced in shoot tips and is transported down the stem Auxin transporter proteins move the hormone from the basal end of one cell into the apical end of the neighboring cell © 2011 Pearson Education, Inc.

17. Figure 39.7 Epidermis Cortex Phloem Xylem Pith RESULTS 100  m 25  m Cell 1 Cell 2 Basal end of cell

18. The Role of Auxin in Cell Elongation According to the acid growth hypothesis, auxin stimulates proton pumps in the plasma membrane The proton pumps lower the pH in the cell wall, activating expansins, enzymes that loosen the wall’s fabric With the cellulose loosened, the cell can elongate © 2011 Pearson Education, Inc.

19. Figure 39.8 Cross-linking polysaccharides Cell wall–loosening enzymes Cellulose microfibril Expansin CELL WALL Plasma membrane CYTOPLASM Plasma membrane Cell wall Nucleus Cytoplasm Vacuole H2OH2O HH HH HH HH HH HH HH HH HH ATP

20. Auxin also alters gene expression and stimulates a sustained growth response © 2011 Pearson Education, Inc.

21. Auxin’s Role in Plant Development Polar transport of auxin plays a role in pattern formation of the developing plant Reduced auxin flow from the shoot of a branch stimulates growth in lower branches Auxin transport plays a role in phyllotaxy, the arrangement of leaves on the stem Polar transport of auxin from leaf margins directs leaf venation pattern The activity of the vascular cambium is under control of auxin transport © 2011 Pearson Education, Inc.

22. Practical Uses for Auxins The auxin indolbutyric acid (IBA) stimulates adventitious roots and is used in vegetative propagation of plants by cuttings An overdose of synthetic auxins can kill plants –For example 2,4-D is used as an herbicide on eudicots © 2011 Pearson Education, Inc.

23. Cytokinins Cytokinins are so named because they stimulate cytokinesis (cell division) © 2011 Pearson Education, Inc.

24. 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.

25. Control of Apical Dominance Cytokinins, auxin, and strigolactone interact in the control of apical dominance, a terminal bud’s ability to suppress development of axillary buds If the terminal bud is removed, plants become bushier © 2011 Pearson Education, Inc.

26. (a) Apical bud intact (not shown in photo) (b) Apical bud removed (c) Auxin added to decapitated stem Axillary buds Lateral branches “Stump” after removal of apical bud Figure 39.9

27. Anti-Aging Effects Cytokinins slow the aging of some plant organs by inhibiting protein breakdown, stimulating RNA and protein synthesis, and mobilizing nutrients from surrounding tissues © 2011 Pearson Education, Inc.

28. Gibberellins Gibberellins have a variety of effects, such as stem elongation, fruit growth, and seed germination © 2011 Pearson Education, Inc.

29. Stem Elongation Gibberellins are produced in young roots and leaves Gibberellins stimulate growth of leaves and stems In stems, they stimulate cell elongation and cell division © 2011 Pearson Education, Inc.

30. Figure 39.10 (a) Rosette form (left) and gibberellin-induced bolting (right) (b)Grapes from control vine (left) and gibberellin-treated vine (right)

31. Fruit Growth In many plants, both auxin and gibberellins must be present for fruit to develop Gibberellins are used in spraying of Thompson seedless grapes © 2011 Pearson Education, Inc.

32. Germination After water is imbibed, release of gibberellins from the embryo signals seeds to germinate © 2011 Pearson Education, Inc.

33. Figure 39.11 Aleurone Endosperm Water Scutellum (cotyledon) Radicle  -amylase Sugar GA 1 2 3

34. Brassinosteroids Brassinosteroids are chemically similar to the sex hormones of animals They induce cell elongation and division in stem segments They slow leaf abscission and promote xylem differentiation © 2011 Pearson Education, Inc.

35. Abscisic Acid Abscisic acid (ABA) slows growth Two of the many effects of ABA –Seed dormancy –Drought tolerance © 2011 Pearson Education, Inc.

36. Seed Dormancy Seed dormancy ensures that the seed will germinate only in optimal conditions In some seeds, dormancy is broken when ABA is removed by heavy rain, light, or prolonged cold Precocious (early) germination can be caused by inactive or low levels of ABA © 2011 Pearson Education, Inc.

37. Figure 39.12 Red mangrove (Rhizophora mangle) seeds Maize mutant Coleoptile

38. Drought Tolerance ABA is the primary internal signal that enables plants to withstand drought ABA accumulation causes stomata to close rapidly © 2011 Pearson Education, Inc.

39. Strigolactones The hormones called strigolactones –Stimulate seed germination –Help establish mycorrhizal associations –Help control apical dominance Strigolactones are named for parasitic Striga plants Striga seeds germinate when host plants exude strigolactones through their roots © 2011 Pearson Education, Inc.

40. Ethylene Plants produce ethylene in response to stresses such as drought, flooding, mechanical pressure, injury, and infection The effects of ethylene include response to mechanical stress, senescence, leaf abscission, and fruit ripening © 2011 Pearson Education, Inc.

41. The Triple Response to Mechanical Stress Ethylene induces the triple response, which allows a growing shoot to avoid obstacles The triple response consists of a slowing of stem elongation, a thickening of the stem, and horizontal growth © 2011 Pearson Education, Inc.

42. Ethylene concentration (parts per million) 0.00 0.10 0.200.40 0.80 Figure 39.13

43. Ethylene-insensitive mutants fail to undergo the triple response after exposure to ethylene Other mutants undergo the triple response in air but do not respond to inhibitors of ethylene synthesis © 2011 Pearson Education, Inc.

44. Figure 39.14 (a) ein mutant (b) ctr mutant ctr mutant ein mutant

45. Senescence Senescence is the programmed death of cells or organs A burst of ethylene is associated with apoptosis, the programmed destruction of cells, organs, or whole plants © 2011 Pearson Education, Inc.

46. Leaf Abscission A change in the balance of auxin and ethylene controls leaf abscission, the process that occurs in autumn when a leaf falls © 2011 Pearson Education, Inc.

47. Figure 39.15 0.5 mm Stem Petiole Protective layer Abscission layer

48. Fruit Ripening A burst of ethylene production in a fruit triggers the ripening process Ethylene triggers ripening, and ripening triggers release of more ethylene Fruit producers can control ripening by picking green fruit and controlling ethylene levels © 2011 Pearson Education, Inc.

49. Systems Biology and Hormone Interactions Interactions between hormones and signal transduction pathways make it hard to predict how genetic manipulation will affect a plant Systems biology seeks a comprehensive understanding that permits modeling of plant functions © 2011 Pearson Education, Inc.

50. Concept 39.3: Responses to light are critical for plant success Light cues many key events in plant growth and development Effects of light on plant morphology are called photomorphogenesis © 2011 Pearson Education, Inc.

51. Plants detect not only presence of light but also its direction, intensity, and wavelength (color) A graph called an action spectrum depicts relative response of a process to different wavelengths Action spectra are useful in studying any process that depends on light © 2011 Pearson Education, Inc.

52. Figure 39.16 (a) Phototropism action spectrum (b) Coleoptiles before and after light exposures 1.0 0.8 0.6 0.4 0.2 0 436 nm 400450 500 550 600 650 700 Wavelength (nm) Phototropic effectiveness Light Time  0 min Time  90 min

53. Different plant responses can be mediated by the same or different photoreceptors There are two major classes of light receptors: blue-light photoreceptors and phytochromes © 2011 Pearson Education, Inc.

54. Blue-Light Photoreceptors Various blue-light photoreceptors control hypocotyl elongation, stomatal opening, and phototropism © 2011 Pearson Education, Inc.

55. Phytochromes as Photoreceptors Phytochromes are pigments that regulate many of a plant’s responses to light throughout its life These responses include seed germination and shade avoidance © 2011 Pearson Education, Inc.

56. Biological Clocks and Circadian Rhythms Many plant processes oscillate during the day Many legumes lower their leaves in the evening and raise them in the morning, even when kept under constant light or dark conditions © 2011 Pearson Education, Inc.

57. Figure 39.20 Noon Midnight

58. Circadian rhythms are cycles that are about 24 hours long and are governed by an internal “clock” Circadian rhythms can be entrained to exactly 24 hours by the day/night cycle The clock may depend on synthesis of a protein regulated through feedback control and may be common to all eukaryotes © 2011 Pearson Education, Inc.

59. The Effect of Light on the Biological Clock Phytochrome conversion marks sunrise and sunset, providing the biological clock with environmental cues © 2011 Pearson Education, Inc.

60. Photoperiodism and Responses to Seasons Photoperiod, the relative lengths of night and day, is the environmental stimulus plants use most often to detect the time of year Photoperiodism is a physiological response to photoperiod © 2011 Pearson Education, Inc.

61. Photoperiodism and Control of Flowering Some processes, including flowering in many species, require a certain photoperiod Plants that flower when a light period is shorter than a critical length are called short-day plants Plants that flower when a light period is longer than a certain number of hours are called long- day plants Flowering in day-neutral plants is controlled by plant maturity, not photoperiod © 2011 Pearson Education, Inc.

62. Concept 39.4: Plants respond to a wide variety of stimuli other than light Because of immobility, plants must adjust to a range of environmental circumstances through developmental and physiological mechanisms © 2011 Pearson Education, Inc.

63. Gravity Response to gravity is known as gravitropism Roots show positive gravitropism; shoots show negative gravitropism Plants may detect gravity by the settling of statoliths, dense cytoplasmic components © 2011 Pearson Education, Inc.

64. Figure 39.24 Statoliths 20  m (a) Primary root of maize bending gravitropically (LMs) (b) Statoliths settling to the lowest sides of root cap cells (LMs)

65. Mechanical Stimuli The term thigmomorphogenesis refers to changes in form that result from mechanical disturbance Rubbing stems of young plants a couple of times daily results in plants that are shorter than controls © 2011 Pearson Education, Inc.

66. Figure 39.25

67. Thigmotropism is growth in response to touch It occurs in vines and other climbing plants Another example of a touch specialist is the sensitive plant Mimosa pudica, which folds its leaflets and collapses in response to touch Rapid leaf movements in response to mechanical stimulation are examples of transmission of electrical impulses called action potentials © 2011 Pearson Education, Inc.

68. (a) Unstimulated state (b) Stimulated state (c) Cross section of a leaflet pair in the stimulated state (LM) Leaflets after stimulation Pulvinus (motor organ) Side of pulvinus with flaccid cells Side of pulvinus with turgid cells Vein 0.5  m Figure 39.26

69. Environmental Stresses Environmental stresses have a potentially adverse effect on survival, growth, and reproduction Stresses can be abiotic (nonliving) or biotic (living) Abiotic stresses include drought, flooding, salt stress, heat stress, and cold stress Biotic stresses include herbivores and pathogens © 2011 Pearson Education, Inc.

70. Drought During drought, plants reduce transpiration by closing stomata, slowing leaf growth, and reducing exposed surface area Growth of shallow roots is inhibited, while deeper roots continue to grow © 2011 Pearson Education, Inc.

71. Flooding Enzymatic destruction of root cortex cells creates air tubes that help plants survive oxygen deprivation during flooding © 2011 Pearson Education, Inc.

72. Salt Stress Salt can lower the water potential of the soil solution and reduce water uptake Plants respond to salt stress by producing solutes tolerated at high concentrations This process keeps the water potential of cells more negative than that of the soil solution © 2011 Pearson Education, Inc.

73. Heat Stress Excessive heat can denature a plant’s enzymes Heat-shock proteins help protect other proteins from heat stress © 2011 Pearson Education, Inc.

74. Cold Stress Cold temperatures decrease membrane fluidity Altering lipid composition of membranes is a response to cold stress Freezing causes ice to form in a plant’s cell walls and intercellular spaces Many plants, as well as other organisms, have antifreeze proteins that prevent ice crystals from growing and damaging cells © 2011 Pearson Education, Inc.

75. Concept 39.5: Plants respond to attacks by herbivores and pathogens Plants use defense systems to deter herbivory, prevent infection, and combat pathogens © 2011 Pearson Education, Inc.

76. Defenses Against Herbivores Herbivory, animals eating plants, is a stress that plants face in any ecosystem Plants counter excessive herbivory with physical defenses, such as thorns and trichomes, and chemical defenses, such as distasteful or toxic compounds Some plants even “recruit” predatory animals that help defend against specific herbivores © 2011 Pearson Education, Inc.

77. Figure 39.28 Wounding Signal transduction pathway Chemical in saliva Synthesis and release of volatile attractants Recruitment of parasitoid wasps that lay their eggs within caterpillars 21134

78. Plants damaged by insects can release volatile chemicals to warn other plants of the same species Arabidopsis can be genetically engineered to produce volatile components that attract predatory mites © 2011 Pearson Education, Inc.

79. Figure 39.UN03

80. Figure 39.UN05