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. Overview: Stimuli and a Stationary Life Linnaeus noted that flowers of different species opened at different times of day and could be used as a___________________, or floral clock Plants, being rooted to the ground, must respond to _______________________that come their way –For example, the ___________________toward light begins with sensing the direction, quantity, and color of the light © 2011 Pearson Education, Inc.

3. Concept 39.1: Signal transduction pathways link signal reception to response A potato left growing in darkness produces shoots that look unhealthy, and it lacks elongated roots These are morphological adaptations for growing in darkness, collectively called _____________ After exposure to light, a potato undergoes changes called ________________, in which shoots and roots grow normally © 2011 Pearson Education, Inc.

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

5. A potato’s response to light is an example of ___________________________ The stages are _________________________ _____________________ © 2011 Pearson Education, Inc.

6. 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

7. Reception Internal and external signals are detected by ______________, proteins that change in response to specific stimuli In ___________________, the receptor is _________________ capable of detecting light © 2011 Pearson Education, Inc.

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

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 ____________________leads to regulation of one or more cellular activities In most cases, these responses to stimulation involve increased activity of _____________ This can occur by ________________ regulation or __________________________ modification © 2011 Pearson Education, Inc.

11. Post-Translational Modification of Preexisting Proteins _________________ modification involves modification of existing proteins in the signal response Modification often involves the ___________________of specific amino acids The second messengers cGMP and Ca 2+ activate ______________________directly © 2011 Pearson Education, Inc.

12. Transcriptional Regulation Specific _____________________bind directly to specific regions of DNA and control transcription of genes Some transcription factors are __________that increase the transcription of specific genes Other transcription factors are ________________that decrease the transcription of specific genes © 2011 Pearson Education, Inc.

13. De-Etiolation (“Greening”) Proteins De-etiolation activates _______________that –Function in _____________________directly –Supply the chemical precursors for ________production –Affect the levels of plant ________________________ that regulate growth © 2011 Pearson Education, Inc.

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

15. The Discovery of Plant Hormones Any response resulting in curvature of organs toward or away from a stimulus is called a _________________ In the late 1800s, Charles Darwin and his son Francis conducted experiments on _________________, a plant’s response to light They observed that a grass seedling could bend toward light only if the ________________was present © 2011 Pearson Education, Inc.

16. They postulated that a ___________ was transmitted from the tip to the elongating region © 2011 Pearson Education, Inc.

17. 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

18. In 1913, Peter Boysen-Jensen demonstrated that the signal was a mobile _______________ _______________ © 2011 Pearson Education, Inc.

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

20. Figure 39.6 Control RESULTS Excised tip on agar cube Growth-promoting chemical diffuses into agar cube Control (agar cube lacking chemical) Offset cubes

21. A Survey of Plant Hormones Plant hormones are produced in very _______ _____________________, but a minute amount can greatly affect growth and development of a plant organ In general, hormones control plant __________ _____________________by affecting the ______________________________of cells © 2011 Pearson Education, Inc.

22. Table 39.1

23. Auxin The term _______ refers to any chemical that promotes elongation of coleoptiles _____________________is a common auxin in plants; in this lecture the term auxin refers specifically to IAA Auxin is produced in ______________and is transported down the stem __________________________move the hormone from the basal end of one cell into the apical end of the neighboring cell © 2011 Pearson Education, Inc.

24. The Role of Auxin in Cell Elongation According to the ___________________, auxin stimulates proton pumps in the plasma membrane The proton pumps lower the pH in the cell wall, activating ______________, enzymes that loosen the wall’s fabric With the cellulose loosened, the cell can ______________________ © 2011 Pearson Education, Inc.

25. 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

26. Auxin also alters ____________________and stimulates a sustained growth response © 2011 Pearson Education, Inc.

27. Auxin’s Role in Plant Development ___________________of auxin plays a role in pattern formation of the developing plant Reduced auxin flow from the shoot of a branch stimulates growth in _______________________ Auxin transport plays a role in _____________, the arrangement of leaves on the stem Polar transport of auxin from leaf margins directs _______________________ pattern The activity of the _____________________is under control of auxin transport © 2011 Pearson Education, Inc.

28. Practical Uses for Auxins The auxin _____________________stimulates adventitious roots and is used in vegetative propagation of plants by cuttings An overdose of synthetic auxins can kill plants –For example ______________ is used as an herbicide on eudicots © 2011 Pearson Education, Inc.

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

30. Control of Cell Division and Differentiation Cytokinins are produced in _____________ tissues such as roots, embryos, and fruits Cytokinins work together with auxin to control cell division and differentiation © 2011 Pearson Education, Inc.

31. Control of Apical Dominance _______________________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.

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

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

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

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

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

37. 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.

38. Abscisic Acid ______________________ slows growth Two of the many effects of ABA –________________ © 2011 Pearson Education, Inc.

39. Seed Dormancy Seed dormancy ensures that the seed will germinate only in _______________________ In some seeds, dormancy is broken when ABA is ____________________ by heavy rain, light, or prolonged cold ____________________________can be caused by inactive or low levels of ABA © 2011 Pearson Education, Inc.

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

41. Strigolactones The hormones called ____________________ 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 _________________through their roots © 2011 Pearson Education, Inc.

42. Ethylene Plants produce _____________ 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.

43. The Triple Response to Mechanical Stress Ethylene induces the ________________, which allows a growing shoot to avoid obstacles The triple response consists of a __________ _________________, a ________________of the stem, and __________________________ © 2011 Pearson Education, Inc.

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

45. Senescence ________________ is the programmed death of cells or organs A burst of _________________is associated with ___________________, 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 ________________, 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 _________________ 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 ______________________________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 ___________ cues many key events in plant growth and development Effects of light on plant morphology are called _________________________ © 2011 Pearson Education, Inc.

51. Plants detect not only presence of light but also its _______________________________(color) A graph called an __________________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: ____________________and ____________________ © 2011 Pearson Education, Inc.

54. Phytochromes as Photoreceptors ___________________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.

55. Phytochromes and Seed Germination Many seeds remain dormant until ____________ conditions change In the 1930s, scientists at the U.S. Department of Agriculture determined the action spectrum for light-induced germination of lettuce seeds © 2011 Pearson Education, Inc.

56. ________ light increased germination, while far- red light inhibited germination The photoreceptor responsible for the opposing effects of red and far-red light is a phytochrome © 2011 Pearson Education, Inc.

57. Figure 39.18 Two identical subunits Chromophore Photoreceptor activity Kinase activity

58. Phytochromes exist in two ________________ _____________, with conversion of P r to P fr triggering many developmental responses _______ light triggers the conversion of P r to P fr _______ light triggers the conversion of P fr to P r The conversion to P fr is faster than the conversion to P r Sunlight increases the ratio of P fr to P r, and triggers germination © 2011 Pearson Education, Inc.

59. Figure 39.19 Synthesis PrPr P fr Red light Far-red light Slow conversion in darkness (some plants) Responses: seed germination, control of flowering, etc. Enzymatic destruction

60. Biological Clocks and Circadian Rhythms Many plant processes _________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.

61. Figure 39.20 Noon Midnight

62. __________________ 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.

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

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

65. Photoperiodism and Control of Flowering Some processes, including ______________in many species, require a certain photoperiod Plants that flower when a light period is shorter than a critical length are called ____________ Plants that flower when a light period is longer than a certain number of hours are called _______ _____________________ Flowering in __________________ is controlled by plant maturity, not photoperiod © 2011 Pearson Education, Inc.

66. Critical Night Length In the 1940s, researchers discovered that flowering and other responses to photoperiod are actually controlled by ____________, not day length © 2011 Pearson Education, Inc.

67. ______________ plants are governed by whether the critical night length sets a ______________ number of hours of darkness ________________ plants are governed by whether the critical night length sets a _____________ number of hours of darkness © 2011 Pearson Education, Inc.

68. ______ light can interrupt the nighttime portion of the photoperiod A flash of red light followed by a flash of far-red light does not disrupt night length Action spectra and photoreversibility experiments show that _______________is the pigment that receives red light © 2011 Pearson Education, Inc.

69. Some plants flower after only a _______ exposure to the required photoperiod Other plants need _____________________of the required photoperiod Still others need an ____________________ in addition to the required photoperiod –For example, ______________________ is a pretreatment with cold to induce flowering © 2011 Pearson Education, Inc.

70. A Flowering Hormone? ___________________ is detected by leaves, which cue buds to develop as flowers The flowering signal is called ____________ Florigen may be a macromolecule governed by the FLOWERING LOCUS T (FT) gene © 2011 Pearson Education, Inc.

71. Figure 39.23 24 hours Graft Short-day plant Long-day plant grafted to short-day plant Long-day plant 24 hours

72. 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 ________________________________ mechanisms © 2011 Pearson Education, Inc.

73. Gravity Response to gravity is known as ____________ __________ show positive gravitropism; __________ show negative gravitropism Plants may detect gravity by the settling of __________________, dense cytoplasmic components © 2011 Pearson Education, Inc.

74. 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)

75. Mechanical Stimuli The term ______________________ 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.

76. Figure 39.25

77. ______________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 _______________________ © 2011 Pearson Education, Inc.

78. (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

79. Environmental Stresses ________________________ have a potentially adverse effect on survival, growth, and reproduction Stresses can be ____________(nonliving) or ____________ (living) ________________stresses include drought, flooding, salt stress, heat stress, and cold stress ________________stresses include herbivores and pathogens © 2011 Pearson Education, Inc.

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

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

82. Figure 39.27 Epidermis Air tubes Vascular cylinder 100  m (a) Control root (aerated) (b) Experimental root (nonaerated)

83. Salt Stress Salt can lower the water potential of the soil solution and ____________________ Plants respond to salt stress by ____________ _____________ tolerated at high concentrations This process keeps the water potential of cells _________________ than that of the soil solution © 2011 Pearson Education, Inc.

84. Heat Stress Excessive heat can _____________ a plant’s enzymes ______________________ help protect other proteins from heat stress © 2011 Pearson Education, Inc.

85. Cold Stress Cold temperatures decrease _________________ Altering ______________________ of membranes is a response to cold stress Freezing causes _____ to form in a plant’s cell walls and intercellular spaces Many plants, as well as other organisms, have ____________________ that prevent ice crystals from growing and damaging cells © 2011 Pearson Education, Inc.

86. Concept 39.5: Plants respond to attacks by herbivores and pathogens Plants use defense systems to deter __________ ___________________, and combat __________ © 2011 Pearson Education, Inc.

87. Defenses Against Herbivores __________________, animals eating plants, is a stress that plants face in any ecosystem Plants counter excessive herbivory with physical defenses, such as ______________ ______________, and chemical defenses, such as distasteful or ___________________ Some plants even “____________” predatory animals that help defend against specific herbivores © 2011 Pearson Education, Inc.

88. Plants damaged by insects can release ______ _________________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.

89. Defenses Against Pathogens A plant’s first line of defense against infection is the barrier presented by the ______________ ______________ If a pathogen penetrates the dermal tissue, the second line of defense is a _______________ that kills the pathogen and prevents its spread This second defense system is enhanced by the plant’s ability to ___________certain pathogens © 2011 Pearson Education, Inc.

90. A _____________ pathogen is one that a plant has little specific defense against An ______________ pathogen is one that may harm but does not kill the host plant © 2011 Pearson Education, Inc. Host-Pathogen Coevolution

91. Systemic Acquired Resistance ______________________causes systemic expression of defense genes and is a long- lasting response ______________________ is synthesized around the infection site and is likely the signal that triggers systemic acquired resistance © 2011 Pearson Education, Inc.

92. Figure 39.UN03