1. Chapter 11 – Plant responses to hormones & environmental stimuli
Responses include
Developmental transitions
Dormancy
Germination
Flowering
Growth

2. Hormones & environmental signals involve signal transduction pathways

3. Internal and external signals

4. Hormones influence gene expression
Gene expression regulated by
microRNAs
transcription factors

5. Plant hormones & growth
(abscisic acid)

8. Hormones interact to promote/inhibit development

9. Auxins
tryptophan

10. Responses involving auxin
Phototropism
Gravitropism
Cellular elongation
Initiation of leaf primordia
Apical dominance
Root development
Fruit development

11. Tropisms
Permanent, directional growth in response to an external stimulus
Positive tropisms
Negative tropisms

12. Phototropism Stems are positively phototropic
How can plants grow towards light?

14. Auxin and cell elongation
Acidification of the cell wall increases elasticity
Acidified cell walls have increased elasticity

16. Phototropism research
Phototropin (NPH1) and phototropism
-initiates a signal transduction pathway
-nph1 mutants non-phototropic

18. Gravitropism

21. Gravitropism
How can it be demonstrated that auxin is involved in gravitropism?

23. Gravitropism and root cap amyloplasts
Gravity regulated auxin transport, Ottenschlaumlger, Iris et al. (2003) Proc. Natl. Acad. Sci. USA 100,

24. Auxin and initiation of leaf primordia
Pin mutant link

25. Responses involving auxin
Apical dominance

26. Responses involving auxin
Formation of adventitious roots

27. Auxin produced by seeds promotes ovary tissue growth

28. Plant hormones Are proteins encoded for by genes
Act individually to bring about changes in plant development
Function as receptors for environmental signals
Both 1 and 3
None of these

29. Auxin Prevents apical dominance Is produced in shoot apical meristems
Promotes seed development inside fruit
All of these
None of these

30. Phototropin Is a type of auxin Promotes apical dominance
Is involved in stem growth towards light
Is produced by seeds
All of these

31. Cytokinins – cell division and differentiation

32. Cytokinin & tissue culture

33. From callus to somatic embryos

35. Gibberellins Promotes: Germination Stem elongation Flowering
Fruit development

36. Gibberellins
Breaking dormancy
Seed germination

37. Gibberellins
Promotes cell division & elongation

39. Gibberellins
Promotes bolting in biennials

40. Gibberellins Promotes: Germination Stem elongation Flowering
Fruit development

42. Gibberellin is part of a complex signal transduction pathway
(see supplemental reading, for related information)

43. Della proteins restrain growth
GA and GID2 degrade Della proteins

44. Gibberellins and germination

45. Gibberellin promotes vegetative growth

46. Abscisic acid
Inhibits growth
Promotes dormancy
Closes stomata

47. Abscisic acid – inhibits germination
Promotes dormancy
Leached by imbibition

48. ABA and stomatal closure

49. ABA delays flowering FCA – an RNA binding protein
FY – an mRNA processing factor
Flowering Locus C – a flowering repressor

50. Ethylene (CH2=CH2) Fruit ripening (promotes) Flowering (inhibits)
Abscission (promotes)
Sex expression in monoecious species (ratio of ♀ to ♂)
Thigmomorphogenesis (reduced stem elongation in some environments)

52. Thigmomorphogenesis

53. Brassinosteroids (BRs)
60 types, brassinolide most common
Stimulates cell elongation, leaf expansion
BR mutants – extreme dwarfs, small crinkled leaves
Dark grown BR mutants – de-etiolated

54. Plant Genes on Steroids Science, Vol 307, Issue 5715, 1569-1570 , 11 March 2005
BIN2 catalyzes breakdown of BES1 & BZR2 proteins (phosphorylation)
BR regulates activity of key growth transcription factors
-BES1(activator)
-BZR1(repressor)

55. Figure (p.290)

56. Figure (p.290)

57. Plant Genes on Steroids Science, Vol 307, Issue 5715, 1569-1570 , 11 March 2005
BIN2 catalyzes breakdown of BES1 & BZR2 proteins (phosphorylation)
BR regulates activity of key growth transcription factors
-BES1(activator)
-BZR1(repressor)

58. Responses to environmental stimuli: light
Phototropism
Stomata opening
Stem elongation
Photodormancy (photoblastism)
Photoperiodism

59. Phytochrome
Phytochromes are proteins with a light absorbing pigment attached (chromophore)
Mediates stem elongation, seed germination, timing of flowering

61. Phytochrome structure

62. Two forms of phytochrome

63. Phytochrome & stem growth
Etiolation occurs in low light or dark …why?
Does Pfr inhibit or promote stem elongation?
Phytochrome and hormonal control of stem elongation

64. Phytochrome and seed germination
Photodormancy & photoblastic seeds
Germination activated by light
Some plants, by red light
Some plants, by far-red light
Negative photoblastism (tomato), Pfr inhibits germination
Positive photoblastism (lettuce), Pfr promotes germination

65. Lettuce is positively photoblastic
30-60% lettuce seed germinate in dark
85-95% lettuce seed germinate in light

66. Phytochrome, photoperiodism & flowering

68. Manipulation of photoperiod
Poinsettia industry
Chrysanthemums
Why won’t my Christmas cactus bloom?

69. Brassinosteroids Promote seed germination in response to light
Promotes flowering in response to day length
Are proteins with an attached light absorbing chromophore
Regulate transcription factors involved in growth
All of these

70. Which of the following is true of phytochrome?
Pfr absorbs red light and Pr absorbs far red light
Pr is the active form of phytochrome and Pfr is the inactive form of phytochrome
Pfr promotes germination in seeds requiring light
All of these
None of these

71. Photoperiodism
Determines seed dormancy/germination in response to light/dark
Determines flowering in response to day length
Is a protein with an attached light absorbing chromophore
Controls stem growth in response to light/dark
All of these

72. Circadian rhythms – sleep movements (nyctinasty)

73. Nyctinasty

75. Solar tracking (heliotropism)

76. Response to mechanical stimuli (seismonasty)

77. Seismonasty – Mimosa pudica

78. Seismonasty

79. Seismonasty
Venus flytrap

80. Response to environmental stimuli: Induced resistance
Herbivore attack, systemin (18aa polypeptide hormone) & jasmonic acid (1-alpha, 2-beta-3-oxo-2-(cis-2-pentenyl)-cyclopentane acetic acid)

81. Figure 1   Model for the activation of defense genes in tomato in response to wounding and insect attack. After wounding, systemin is released from its precursor prosystemin by proteolytic processing. Systemin subsequently binds a membrane-bound receptor to initiate an intracellular signaling cascade, including the activities of a MAP kinase, a phospholipase, a calcium dependent protein kinase, an extracellular alkalinization, and the release of linlenic acid from membranes. Linolenic acid is converted to jasmonic acid, a messenger for early defense gene activation. Catalytic activity of polygalaturonase, an early gene, leads to generation of hydrogen peroxide acting as a second messenger for late gene activation. R, receptor; MAPK, MAP kinase; Ca2+PK; calcium dependent protein kinase; PLA2, phospholipase A2; LA, linolenic acid; JA, jasmonic acid; pm, plasma membrane.
H2O2 prevents cell wall digestion by fungal pectinases

82. Response to environmental stimuli: Induced resistance
Pathogens & the hypersensitive response (HR)

83. HR response & systemic acquired resistance (SAR)

84. SAR responses Lignification of cell walls Antimicrobial molecules
PR-proteins (pathogen related proteins)
Chitinases
Phytoalexins (inhibit protein synthesis

85. SAR model