1. © 2012 Pearson Education, Inc. Lecture by Edward J. Zalisko PowerPoint Lectures for Campbell Biology: Concepts & Connections, Seventh Edition Reece, Taylor, Simon, and Dickey Chapter 33 Control Systems in Plants

2. Introduction  Soy protein is one of the few plant proteins that provide all of the essential amino acids.  Benefits of consuming soy include –lowered risk of heart disease, –high levels of antioxidants and fiber, –low levels of fat, and –Lowering LDL (“bad cholesterol”) levels while maintaining HDL levels. © 2012 Pearson Education, Inc.

3. Introduction  Soy contains phytoestrogens, hormones that can reduce the symptoms of menopause in women and can help –reduce the risks of heart disease and –sustain bone mass.  However, high levels of estrogens appear to increase the risk of –breast cancer and –ovarian cancer. © 2012 Pearson Education, Inc.

4. Figure 33.0_1 Chapter 33: Big Ideas Plant HormonesResponses to Stimuli

5. Figure 33.0_2

6. PLANT HORMONES © 2012 Pearson Education, Inc.

7. 33.1 Experiments on how plants turn toward light led to the discovery of a plant hormone  Any growth response that results in plant organs curving toward or away from stimuli is called a tropism.  The growth of a shoot in response to light is called phototropism. –Moving toward sunlight helps a growing plant use sunlight to drive photosynthesis. –Phototropism can result when the cells on the dark side of a plant stem elongate faster than those on the light side. © 2012 Pearson Education, Inc.

8. Video: Phototropism Use window controls to play

9. Figure 33.1A

10. Figure 33.1B Illuminated side of shoot Light Shaded side of shoot

11. 33.1 Experiments on how plants turn toward light led to the discovery of a plant hormone  Studies of plant responses to light led to the first evidence of plant hormones, a chemical signal –produced in one part of the body and –transported to other parts, –where it acts on target cells to change their functioning.  Charles Darwin and his son Francis conducted experiments that showed that the shoot tips of plants controlled their ability to grow toward light. © 2012 Pearson Education, Inc.

12.  The Darwins’ experiments –When plant tips were removed, plants did not grow toward light. –When plant tips were covered with an opaque cap, they did not grow toward light. –When plant tips were covered with a clear tip, they did grow toward light. 33.1 Experiments on how plants turn toward light led to the discovery of a plant hormone © 2012 Pearson Education, Inc.

13. Figure 33.1C Light Control Tip removed Tip covered by opaque cap Tip covered by trans- parent cap Base covered by opaque shield 12 3 4 Darwin and Darwin (1880) 5 Tip separated by gelatin block Boysen-Jensen (1913) 6 Tip separated by mica

14. Figure 33.1C_1 Light Control Tip removed Tip covered by opaque cap Tip covered by trans- parent cap Base covered by opaque shield Darwin and Darwin (1880) 12 3 4

15.  Peter Boysen-Jensen later conducted experiments that showed that chemical signals produced in shoot tips were responsible for phototropism.  Jensen’s experiment –When a gelatin block that allowed chemical diffusion was placed below the shoot tip, plants grew toward light. –When a mica block that prevented chemical diffusion was placed below the shoot tip, plants did not grow toward light. 33.1 Experiments on how plants turn toward light led to the discovery of a plant hormone © 2012 Pearson Education, Inc.

16. Figure 33.1C_2 Tip separated by gelatin block Boysen-Jensen (1913) Tip separated by mica Light 5 6

17.  A graduate student named Frits Went isolated the chemical hormone responsible for phototropism. –Plant tips were placed on an agar block to allow the chemical signal molecules to diffuse from the plant tip to the agar. –When agar blocks containing chemical signals were centered on the ends of “decapitated” plants, they grew straight. –When agar blocks were offset to one side of the “decapitated” plants, they bent away from the side with the agar block. 33.1 Experiments on how plants turn toward light led to the discovery of a plant hormone © 2012 Pearson Education, Inc.

18. –Went concluded that a chemical produced in the shoot tip was transferred down through the plant, and high concentration of that chemical increased cell elongation on the dark side of the plant.  The chemical signal responsible for phototropism is a hormone that Went called auxin. 33.1 Experiments on how plants turn toward light led to the discovery of a plant hormone © 2012 Pearson Education, Inc.

19. Figure 33.1D_s1 Control No light A chemical diffuses from the shoot tip into the agar block. Agar The block stimulates growth. 1

20. Figure 33.1D_s2 Control No light A chemical diffuses from the shoot tip into the agar block. Agar The block stimulates growth. Offset blocks stimulate curved growth. 1 2

21. Figure 33.1D_s3 Control No light A chemical diffuses from the shoot tip into the agar block. Agar The block stimulates growth. Offset blocks stimulate curved growth. Blocks with no chemical have no effect. 1 2 3

22. 33.2 Five major types of hormones regulate plant growth and development  Plant hormones –are produced in very low concentrations but –can have a profound effect on growth and development.  The binding of hormones to cell-surface receptors triggers a signal transduction pathway that –amplifies the hormonal signal and –leads to a response or responses within the cell. © 2012 Pearson Education, Inc.

23.  Plant biologists have identified five major types of plant hormones. –Other important hormones exist, but will not be discussed here. –Some of the hormones listed in Table 33.2 represent a group of related hormones. 33.2 Five major types of hormones regulate plant growth and development © 2012 Pearson Education, Inc.

24.  As indicated in Table 33.2, each hormone has multiple effects, depending on –its site of action, –its concentration, and –the developmental stage of the plant. 33.2 Five major types of hormones regulate plant growth and development © 2012 Pearson Education, Inc.

25. Table 33.2

26. 33.3 Auxin stimulates the elongation of cells in young shoots  Auxin is the term for any chemical substance that promotes seedling elongation.  Indoleacetic acid (IAA) is the –major natural auxin found in plants and –type of auxin referred to in this chapter.  Auxin is produced in apical meristems at the tips of shoots. © 2012 Pearson Education, Inc.

27. Figure 33.3A

28. 33.3 Auxin stimulates the elongation of cells in young shoots  At different concentrations, auxin –stimulates or inhibits the elongation of shoots and roots, –may act by weakening cell walls, allowing them to stretch when cells take up water, –stimulates the development of vascular tissues and cell division in the vascular cambium, promoting growth in stem diameter, and –is produced by developing seeds and promotes the growth of fruit. © 2012 Pearson Education, Inc.

29. Figure 33.3B Stems Roots Increasing auxin concentration (g/L) 10  8 10  6 10  4 10  2 1 10 2 0.9 g/L Inhibition Promotion Elongation 0  

30. Figure 33.3C 2 C ELL W ALL 4 Enzyme that separates cross-linking molecules 3 1 C YTOPLASM Proton pump (protein) Plasma membrane Cell wall Enzyme that loosens cell wall Plasma membrane Cellulose microfibril Cross-linking molecule Vacuole H2OH2O HH HH HH HH HH HH HH HH HH

31. Figure 33.3C_1 C ELL W ALL Enzyme that separates cross-linking molecules 3 C YTOPLASM Proton pump (protein) Plasma membrane Enzyme that loosens cell wall Cellulose microfibril Cross-linking molecule HH HH HH HH HH HH HH HH HH 2 1

32. 33.4 Cytokinins stimulate cell division  Cytokinins –promote cytokinesis, or cell division, –are produced in actively growing organs such as roots, embryos, and fruits, and –move upward from roots through a plant, –balancing the effects of auxin from apical meristems and –causing lower buds to develop into branches. © 2012 Pearson Education, Inc.

33. Figure 33.4 Terminal bud No terminal bud

34. 33.5 Gibberellins affect stem elongation and have numerous other effects  Gibberellins –promote cell elongation and cell division in stems and leaves and –were named for a genus of fungi that produce the same chemical and cause “foolish seedling” disease, in which rice seedlings grew so tall and spindly that they toppled over before producing grain. –There are more than 100 distinct gibberellins produced primarily in roots and young leaves. © 2012 Pearson Education, Inc.

35.  Gibberellins also promote –fruit development and –seed germination.  In some plants, gibberellins interact antagonistically with abscisic acid. 33.5 Gibberellins affect stem elongation and have numerous other effects © 2012 Pearson Education, Inc.

36. Figure 33.5A Dwarf plant (untreated) Dwarf plant treated with gibberellins

37. Figure 33.5B

38. Figure 33.5C

39. 33.6 Abscisic acid inhibits many plant processes  Abscisic acid (ABA) is a plant hormone that inhibits growth.  High concentrations of ABA promote seed dormancy. –ABA must be removed for germination to occur. –The ratio of ABA to gibberellins controls germination.  ABA also acts as a “stress hormone,” causing stomata to close when a plant is dehydrated. © 2012 Pearson Education, Inc.

40. Figure 33.6

41. 33.7 Ethylene triggers fruit ripening and other aging processes  Ethylene is a –gaseous by-product of coal combustion and –naturally occurring plant hormone.  Plants produce ethylene, which triggers –fruit ripening and –programmed cell death.  Ethylene is also produced in response to stresses such as drought, flooding, injury, or infection. © 2012 Pearson Education, Inc.

42.  A changing ratio of auxin to ethylene, triggered mainly by shorter days, probably causes –autumn color changes and –the loss of leaves from deciduous trees.  When an autumn leaf falls, the base of the leaf separates from the stem. –The separation region is called the abscission layer, and –the leaf drops off when its weight splits the abscission layer apart. 33.7 Ethylene triggers fruit ripening and other aging processes © 2012 Pearson Education, Inc.

43. Figure 33.7A

44. Figure 33.7B Leaf stalk (petiole) Stem Protective layerAbscission layer Leaf stalkStem

45. Figure 33.7B_1 Leaf stalk (petiole) Stem

46. Figure 33.7B_2 Protective layerAbscission layer Leaf stalk Stem

47. 33.8 CONNECTION: Plant hormones have many agricultural uses  Agricultural uses of plant hormones include –control of fruit production, ripening, and dropping, –production of seedless fruits, and –use as weed killers.  Agricultural uses of plant hormones –help keep food prices down and can benefit the environment in aspects such as soil erosion, but –may have dangerous side effects for humans and the environment. © 2012 Pearson Education, Inc.

48. Figure 33.8

49. Figure 33.8_UN

50. RESPONSES TO STIMULI © 2012 Pearson Education, Inc.

51. 33.9 Tropisms orient plant growth toward or away from environmental stimuli  Tropisms are responses that cause plants to grow in response to environmental stimuli. –Positive tropisms cause plants to grow toward a stimulus. –Negative tropisms cause plants to grow away from a stimulus.  Plants respond to various environmental stimuli. –Phototropism is a response to light. –Gravitropism is a response to gravity. –Thigmotropism is a response to touch. © 2012 Pearson Education, Inc.

52. Video: Gravitropism Use window controls to play

53. © 2012 Pearson Education, Inc. Video: Mimosa Leaf Use window controls to play

54. Figure 33.9A

55. Figure 33.9B

56. 33.10 Plants have internal clocks  Plants display rhythmic behavior including the –opening and closing of stomata and –folding and unfolding of leaves and flowers.  A circadian rhythm –is an innate biological cycle of about 24 hours and –may persist even when an organism is sheltered from environmental cues. © 2012 Pearson Education, Inc.

57. 33.10 Plants have internal clocks  Research on a variety of organisms indicates that circadian rhythms are controlled by internal timekeepers known as biological clocks.  Environmental cues such as light/dark cycles keep biological clocks precisely synchronized.  For most organisms, including plants, we know little about –where the clocks are located or –what kinds of cells are involved. © 2012 Pearson Education, Inc.

58. Figure 33.10 NoonMidnight

59. 33.11 Plants mark the seasons by measuring photoperiod  Biological clocks can influence seasonal events including –flowering, –seed germination, and –the onset of dormancy.  The environmental stimulus plants most often use to detect the time of year is called photoperiod, the relative lengths of day and night. © 2012 Pearson Education, Inc.

60.  Plant flowering signals are determined by night length.  Short-day plants, such as chrysanthemums and poinsettias –generally flower in the late summer, fall, or winter –when light periods shorten.  Long-day plants, such as spinach, lettuce, and many cereal grains –generally flower in late spring or early summer –when light periods lengthen. 33.11 Plants mark the seasons by measuring photoperiod © 2012 Pearson Education, Inc.

61. Figure 33.11 Short- day (long- night) plants Long- day (short- night) plants Plants bloom only with a shorter dark period. Flash of light induces flowering. Flash of light prevents flowering. Plants bloom only with a longer dark period. Darkness Flash of light Light 0 24Time (hrs) 1 2 3 4 5 6 Critical dark period

62. Figure 33.11_1 Short- day (long- night) plants Flash of light prevents flowering. Plants bloom only with a longer dark period. Darkness Flash of light Light 0 24 Time (hrs) 1 2 3

63. Figure 33.11_2 Long- day (short- night) plants Plants bloom only with a shorter dark period. Flash of light induces flowering. Critical dark period 0 24 Time (hrs) 6 5 4

64. 33.12 Phytochromes are light detectors that may help set the biological clock  Phytochromes –are proteins with a light-absorbing component and –may help plants set their biological clock and monitor photoperiod.  Phytochromes detect light in the red and far-red wavelengths. –One form of phytochrome absorbs red light (P r ). –One form detects far-red light (P fr ). –When P r absorbs light, it is converted into P fr. –When P fr absorbs light, it is converted into P r. © 2012 Pearson Education, Inc.

65. Figure 33.12A Red light Far-red light P fr PrPr R a p i d c o nv e r s i o n n i d a y l i g h t S l o w c o n v e r s i o n s s e n k r a d n i

66. –P r is naturally produced during dark hours, while P fr is broken down. –The relative amounts of P r and P fr present in a plant change as day length changes. 33.12 Phytochromes are light detectors that may help set the biological clock © 2012 Pearson Education, Inc.

67. Figure 33.12B Time (hrs)024 R RFR R R R R Critical dark period Short-day (long-night) plant Long-day (short-night) plant 1 2 3 4

68. 33.13 EVOLUTION CONNECTION: Defenses against herbivores and infectious microbes have evolved in plants  Herbivores are animals that mainly eat plants.  Plants use chemicals to defend themselves against herbivores and pathogens.  Plants counter herbivores with –physical defenses, such as thorns, and –chemical defenses, such as distasteful or toxic compounds. © 2012 Pearson Education, Inc.

69. Figure 33.13A_s1 Plant cell Damage to plant and chemical in caterpillar saliva 1

70. Figure 33.13A_s2 Plant cell Damage to plant and chemical in caterpillar saliva 1 2 Signal transduction pathway

71. Figure 33.13A_s3 Plant cell Damage to plant and chemical in caterpillar saliva 1 2 Signal transduction pathway Synthesis and release of chemical attractants 2 3

72. Figure 33.13A_s4 Plant cell Damage to plant and chemical in caterpillar saliva 1 2 Signal transduction pathway Synthesis and release of chemical attractants 3 Wasp is attracted 4

73. Figure 33.13A_s5 Plant cell Damage to plant and chemical in caterpillar saliva 1 2 Signal transduction pathway Synthesis and release of chemical attractants 3 Wasp is attracted 4 The wasp lays eggs 5

74. Figure 33.13A_2

75. 33.13 EVOLUTION CONNECTION: Defenses against herbivores and infectious microbes have evolved in plants  Plants defend themselves against pathogens at several levels. –The first line of defense against infection is the physical barrier of the plant’s epidermis. –If that fails, plant cells damaged by infection –seal off the infected areas and –release microbe-killing chemicals that signal nearby cells to mount a similar chemical defense. –In addition, hormones trigger generalized defense responses in other organs in the process of systemic acquired resistance. © 2012 Pearson Education, Inc.

76. Figure 33.13B_s1 R protein Binding of the pathogen’s Avr protein to the plant’s R protein 1 Avr protein Avirulent pathogen

77. Figure 33.13B_s2 R protein Binding of the pathogen’s Avr protein to the plant’s R protein 1 Avr protein Avirulent pathogen 2 Signal transduction pathway

78. Figure 33.13B_s3 R protein Binding of the pathogen’s Avr protein to the plant’s R protein 1 Avr protein Avirulent pathogen 3 2 Signal transduction pathway Enhanced local response Recognition between R and Avr proteins, leading to a strong local response

79. Figure 33.13B_s4 R protein Binding of the pathogen’s Avr protein to the plant’s R protein 1 Avr protein Avirulent pathogen 2 Signal transduction pathway 3 Enhanced local response Recognition between R and Avr proteins, leading to a strong local response 4 Hormones

80. Figure 33.13B_s5 R protein Binding of the pathogen’s Avr protein to the plant’s R protein 1 Avr protein Avirulent pathogen 2 Signal transduction pathway 4 Hormones 3 Enhanced local response 5 Signal transduction pathway Recognition between R and Avr proteins, leading to a strong local response

81. Figure 33.13B_s6 R protein Binding of the pathogen’s Avr protein to the plant’s R protein 1 Avr protein Avirulent pathogen 2 Signal transduction pathway 4 Hormones 3 Enhanced local response 5 Signal transduction pathway Recognition between R and Avr proteins, leading to a strong local response 6 Additional defensive chemicals Systemic acquired resistance

82. You should now be able to 1.Describe the experiments and conclusions of the phototropism research performed by the Darwins, Boysen-Jensen, and Went. 2.Describe the functions of the five major types of plant hormones. 3.Describe the uses of plant hormones in modern agriculture and the ethical issues associated with their use. 4.Define phototropism, gravitropism, and thigmotropism. © 2012 Pearson Education, Inc.

83. 5.Explain how biological clocks work and how they influence the lives of plants. 6.Distinguish between short-day plants and long-day plants. 7.Describe the roles of phytochromes in plants. 8.Explain how plants defend themselves against herbivores. You should now be able to © 2012 Pearson Education, Inc.

84. Figure 33.UN01 Light Gravity PhototropismGravitropismThigmotropism

85. Figure 33.UN02 Critical dark period Critical dark period Long-day (short-night) plants Short-day (long-night) plants

86. Figure 33.UN03 (a) stimulates (b) (e) stimulates inhibits enhances Cell elongation Axillary bud growth stimulates inhibits (c) (d) (g) opposes (h) opposes stimulates Seed dormancy Leaf abscission stimulates (f) opposes