1. Growth regulators
All are small organics: made in one part, affect another part
Treating a plant tissue with a hormone is like putting a dime in a vending machine. It depends on the machine, not the dime!

2. Auxin
First studied by Darwins!
Showed that a "transmissible influence" made at tips caused bending lower down
No tip, no curve!

3. Auxin
1919: Paal showed that if tip was replaced asymmetrically, plant grew asymmetrically even in dark
Uneven amounts of "transmissible influence" makes bend
1926: Went showed that a chemical that diffused from tips into blocks caused growth
If placed asymmetrically get bending due to asymmetrical growth
Amount of bending depends on [auxin]
1934: Indole-3-Acetic acid (IAA) from the urine of pregnant women was shown to cause bending

4. IAA Auxin IAA is the main auxin in vivo.
Many synthetic auxins have been identified
No obvious structural similarity, yet all work!
IAA

5. IAA Auxin IAA is the main auxin in vivo.
Many synthetic auxins have been identified
No obvious structural similarity, yet all work!
Widely used in agriculture
to promote growth (flowering, cuttings)
IAA

6. IAA Auxin weed killers! Agent orange was 1:1 2,4-D and 2,4,5-T
2,4,5-T was contaminated with dioxin
2,4-D is still widely used: selectively kills dicots
Controls weeds in monocot crops (corn, rice, wheat)
Mech unclear: may cause excess ethylene
or ABA production.
IAA

7. Auxin
>90%of IAA is conjugated to sugars in vivo!

8. Auxin
>90%of IAA is conjugated to sugars in vivo!
Inactive, but readily activated!

9. Auxin
>90%of IAA is conjugated to sugars in vivo!
Inactive, but readily activated!
Best way to measure [auxin] is bioassay!

10. Auxin
>90%of IAA is conjugated to sugars in vivo!
Inactive, but readily activated!
Best way to measure [auxin] is bioassay!
Critical concentration varies between tissues

11. Auxin
>90%of IAA is conjugated to sugars in vivo!
Inactive, but readily activated!
Best way to measure [auxin] is bioassay!
Critical concentration varies between tissues
Roots are much more sensitive
than leaves!

12. Auxin
Critical concentration varies between tissues
Roots are much more sensitive than leaves!
Made in leaves & transported to roots so [IAA] decreases going down the plant
Most cells are IAA sinks!

13. Auxin Synthesis
Made in leaves & transported to roots so [IAA] decreases going down the plant
Most is made from trp

14. Auxin Synthesis
Most is made from trp
Also made by trp-independent pathway: exits before trp

15. Auxin Synthesis
Most is made from trp
Also made by trp-independent pathway: exits before trp
Path used varies
between tissues

16. Auxin Synthesis
Most is made from trp
Also made by trp-independent pathway: exits before trp
Path used varies
between tissues
No way to run
out of IAA

17. Auxin Levels
No way to run out of IAA! [IAA] depends on metabolism

18. Auxin Levels
No way to run out of IAA!
[IAA] depends on metabolism
Most cells are IAA sinks!

19. Auxin Levels
No way to run out of IAA!
[IAA] depends on metabolism
Most cells are IAA sinks!
IAA is made at shoot apex &
transported down: basipetal

20. Auxin Levels
No way to run out of IAA!
[IAA] depends on metabolism
Most cells are IAA sinks!
IAA is made at shoot apex &
transported down: basipetal
IAA transport therefore affects
growth & development

21. Auxin Transport
IAA transport therefore affects growth & development
is polar and basipetal: New roots form at base of stem even if stored upside-down

22. Auxin Transport
IAA transport therefore affects development: is polar and basipetal. New roots form at base of stem even if stored upside-down.
Stem sections
only move IAA
basipetally

23. Chemiosmotic Auxin Transport
Apoplastic IAAH diffuses
into cell
IAAH due to low pH

24. Chemiosmotic Auxin Transport
Apoplastic IAAH diffuses
into cell
IAAH due to low pH
AUX1 pumps in IAA- -

25. Chemiosmotic Auxin Transport
Apoplastic IAAH diffuses
into cell
IAAH due to low pH
AUX1 pumps in IAA-
2. In cell IAAH-> IAA- due
to pH 7.2 -

26. Chemiosmotic Auxin Transport
Apoplastic IAAH diffuses
into cell
IAAH due to low pH
AUX1 pumps in IAA-
2. In cell IAAH-> IAA- due
to pH 7.2, , draws more IAAH -

27. Chemiosmotic Auxin Transport
Apoplastic IAAH diffuses
into cell
IAAH due to low pH
AUX1 pumps in IAA-
2. In cell IAAH-> IAA- due
to pH 7.2, draws more IAAH
3. IAA- is pumped out by PIN
proteins in basal part of cell -

28. Chemiosmotic Auxin Transport
Apoplastic IAAH diffuses
into cell
IAAH due to low pH
AUX1 pumps in IAA-
2. In cell IAAH-> IAA- due
to pH 7.2, draws more IAAH
3. IAA- is pumped out by PIN
proteins in basal part of cell
4. In apoplast IAA- ->
Cycle repeats

29. Chemiosmotic Auxin Transport
Supporting evidence
Some chemicals specifically
block import or export

30. Chemiosmotic Auxin Transport
Supporting evidence
Some chemicals specifically
block import or export
Export blockers stop efflux
into block, no effect on uptake

31. Chemiosmotic Auxin Transport
Supporting evidence
Some chemicals specifically
block import or export
Export blockers stop efflux
into block, no effect on uptake
Import blockers stop uptake

32. Chemiosmotic Auxin Transport
Supporting evidence
Some chemicals specifically block import or export
Export blockers stop efflux , no effect on uptake
Import blockers stop uptake
Both mess up development!

33. Chemiosmotic Auxin Transport
Supporting evidence
Some chemicals specifically block import or export
Export blockers stop efflux , no effect on uptake
Import blockers stop uptake
Both mess up development!
Natural transport inhibitors have anti-cancer activity!

34. Chemiosmotic Auxin Transport
Supporting evidence
Some chemicals specifically block import or export
Export blockers stop efflux , no effect on uptake
Import blockers stop uptake
Both mess up development!
Natural transport inhibitors have anti-cancer activity!
Genistein binds estrogen receptors

35. Chemiosmotic Auxin Transport
Supporting evidence
Some chemicals specifically block import or export
Both mess up development!
2.AUX1 encodes an IAA-H+ symporter found at top of cell

36. Chemiosmotic Auxin Transport
Supporting evidence
Some chemicals specifically block import or export
Both mess up development!
2.AUX1 encodes an IAA-H+ symporter found at top of cell
aux1 resemble
plants treated with
import blockers

37. Chemiosmotic Auxin Transport
Supporting evidence
Some chemicals specifically block import or export
2.AUX1 encodes an IAA-H+ symporter found at top of cell
aux1 resemble plants treated with import blockers
3. PINs encode IAA
exporters found at cell base

38. Chemiosmotic Auxin Transport
Supporting evidence
Some chemicals specifically block import or export
2.AUX1 encodes an IAA-H+ symporter found at top of cell
aux1 resemble plants treated with import blockers
3. PINs encode IAA
exporters found at cell base
pin1 resemble plants treated
with export blockers

39. Auxin Action
Two models:
Acid growth: IAA starts H+ pumping that loosens cell wall

40. Auxin Action
Two models:
Acid growth: IAA starts H+ pumping that loosens cell wall
Low pH is sufficient to cause elongation

41. Auxin Action
Two models:
Acid growth: IAA starts H+ pumping that loosens cell wall
Low pH is sufficient to cause elongation
H+ pump activators cause elongation

42. Auxin Action
Two models:
Acid growth: IAA starts H+ pumping that loosens cell wall
Gene activation

43. Auxin Action
IAA activates cell elongation & transcription in targets

44. Auxin Action
IAA activates cell elongation & transcription in targets
Elongation has lag of 10'

45. Auxin Action
IAA activates cell elongation & transcription in targets
Elongation has lag of 10'
IAA induces PM H+ pump with 10' lag

46. Auxin Action
IAA induces PM H+ pump with 10' lag
Acid- growth: IAA-induced pH drop
activates expansins & glucanases

47. Auxin Action
IAA induces PM H+ pump with 10' lag
Acid- growth: IAA-induced pH drop activates expansins & glucanases
Lag may represent time needed to move H+ pump to PM

48. Active transport
H+ pumps
lower pH in lysosomes, stomach

49. Auxin Action
IAA induces PM H+ pump with 10' lag
Acid- growth: IAA-induced pH drop activates expansins & glucanases
Lag may represent time needed to move H+ pump to PM
Gnom mutants stop transport of PIN1 to PM = links GTP exchange factor & development

50. Auxin Action
IAA induces PM H+ pump with 10' lag
Acid- growth: IAA-induced pH drop activates expansins & glucanases
Lag may represent time needed to move H+ pump to PM
Also have SAUR genes expressed w/in 10'!

51. Auxin Action
Acid- growth: IAA-induced pH drop activates expansins & glucanases
Phototropism is due to more elongation on shaded side

52. Auxin Action
Acid- growth: IAA-induced pH drop activates extensins & glucanases
Phototropism is due to more elongation on shaded side due to lateral IAA redistribution

53. Auxin Action
Acid- growth: IAA-induced pH drop activates extensins & glucanases
Phototropism is due to more elongation on shaded side due to lateral IAA redistribution
IAA export blockers
stop phototropism

54. Auxin Action
Phototropism is due to more elongation on shaded side due to lateral IAA redistribution
IAA export blockers stop phototropism
PIN1 goes away in cells on
light side & PIN3 on cell
sides takes over

55. Auxin Action
Phototropism is due to more elongation on shaded side due to lateral IAA redistribution
IAA export blockers stop phototropism
PIN1 goes away in cells on
light side & PIN3 on cell
sides takes over
IAA moves sideways

56. Auxin Action
Phototropism is due to more elongation on shaded side due to lateral IAA redistribution
IAA export blockers stop phototropism
PIN1 goes away in cells on
light side & PIN3 on cell
sides takes over
IAA moves sideways
Lower pH on shaded side
enhances IAA uptake

57. Auxin Action
Gravitropism
Shoots bend up!

58. Auxin Action
Gravitropism
Shoots bend up!
Roots bend down!

59. Auxin Action
Gravitropism
Shoots bend up!
Roots bend down!
Both effects are due to IAA redistribution to lower side!

60. Auxin Action
Gravitropism
Shoots bend up, Roots bend down
Both effects are due to IAA
redistribution to lower side!
[IAA] stimulates shoots
& inhibits roots!

61. Apical dominance
Auxin inhibits lateral bud formation
decapitate plant and lateral buds develop

62. Apical dominance
Auxin inhibits lateral bud formation
decapitate plant and lateral buds develop
apply IAA to cut tip & lateral buds do not develop

63. Apical dominance
Auxin induces lateral & adventitious roots

64. Apical dominance
Auxin induces lateral & adventitious roots
Promotes cell division at initiation site

65. Apical dominance
Auxin induces lateral & adventitious roots
Promotes cell division at initiation site
Promotes cell elongation & viability as root grows

66. Auxin signaling
Used "auxin-resistant" mutants to find genes involved in auxin signaling

67. Auxin signaling
Used "auxin-resistant" mutants to find genes involved in auxin signaling
Many are involved in selective protein
degradation!

68. Auxin signaling
Used "auxin-resistant" mutants to find genes involved in auxin signaling
Many are involved in selective protein degradation!
Some auxin receptors, eg TIR1 are E3 ubiquitin ligases!

69. Auxin signaling
Auxin receptors eg TIR1 are E3 ubiquitin ligases!
Upon binding auxin they activate complexes targeting AUX/IAA proteins for degradation!

70. Auxin signaling
Auxin receptors eg TIR1 are E3 ubiquitin ligases!
Upon binding auxin they activate complexes targeting AUX/IAA proteins for degradation!
AUX/IAA inhibit ARF
transcription factors,
so this turns on
"early genes"

71. Auxin signaling
Auxin receptors eg TIR1 are E3 ubiquitin ligases!
Upon binding auxin they activate complexes targeting AUX/IAA proteins for degradation!
AUX/IAA inhibit ARF
transcription factors,
so this turns on
"early genes"
Some early genes turn on
'late genes" needed for
development

72. Auxin signaling
ABP1 is a different IAA receptor localized in ER
Activates PM H+ pump by sending it to PM & keeping it there

73. Auxin signaling
ABP1 is a different IAA receptor localized in ER
Activates PM H+ pump by sending it to PM & keeping it there
Does not affect gene expression!

74. Auxin & other growth regulators
ABP1 is a different IAA receptor localized in ER
Stimulates PM H+ pump by sending it to PM & keeping it there.
Does not affect gene expression!
Some "late genes" synthesize ethylene (normally a wounding response): how 2,4-D kills?

75. Auxin & other growth regulators
Some "late genes" synthesize ethylene (normally a wounding response): how 2,4-D kills?
Auxin/cytokinin determines
whether callus forms roots or shoots

76. Cytokinins
Discovered as factors which induce cultured cells to divide
Haberlandt (1913): phloem chemical stimulates division

77. Cytokinins
Discovered as factors which induce cultured cells to divide
Haberlandt (1913): phloem chemical stimulates division
van Overbeek (1941): coconut milk stimulates division

78. Cytokinins
Discovered as factors which induce cultured cells to divide
Haberlandt (1913): phloem chemical stimulates division
van Overbeek (1941): coconut milk stimulates division
Miller… Skoog (1955): degraded DNA stimulates division!

79. Cytokinins
Discovered as factors which induce cultured cells to divide
Haberlandt (1913): phloem chemical stimulates division
van Overbeek (1941): coconut milk stimulates division
Miller… Skoog (1955): degraded DNA stimulates division!
Kinetin was the breakdown product

80. Cytokinins
Discovered as factors which induce cultured cells to divide
Haberlandt (1913): phloem chemical stimulates division
van Overbeek (1941): coconut milk stimulates division
Miller… Skoog (1955): degraded DNA stimulates division!
Kinetin was the breakdown product
Derived from adenine

81. Cytokinins
Discovered as factors which induce cultured cells to divide
Haberlandt (1913): phloem chemical stimulates division
van Overbeek (1941): coconut milk stimulates division
Miller… Skoog (1955): degraded DNA stimulates division!
Kinetin was the breakdown product
Derived from adenine
Requires auxin to stimulate division

82. Cytokinins
Requires auxin to stimulate division
Kinetin/auxin determines tissue formed (original fig)

83. Cytokinins
Requires auxin to stimulate division
Kinetin/auxin determines tissue formed
Inspired search for natural cytokinins
Miller& Letham (1961) ± simultaneously found zeatin in corn
Kinetin trans- Zeatin

84. Cytokinins
Miller& Letham (1961) ± simultaneously found zeatin
Later found in many spp including coconut milk
Kinetin trans-Zeatin

85. Cytokinins
Miller& Letham (1961) ±
simultaneously found zeatin
Later found in many spp
including coconut milk
Trans form is more active,
but both exist (& work)
Many other natural &
synthetics have been identified

86. Cytokinins
Many other natural & synthetics have been identified
Like auxins, many are bound to sugars or nucleotides

87. Cytokinins
Many other natural & synthetics have been identified
Like auxins, many are bound to sugars or nucleotides
Inactive, but easily converted

88. Cytokinin Synthesis
Most cytokinins are made at root
apical meristem & transported to
sinks in xylem

89. Cytokinin Synthesis
Most cytokinins are made at root
apical meristem & transported to
sinks in xylem
Therefore have inverse gradient
with IAA

90. Cytokinin Synthesis
Most cytokinins are made at root
apical meristem & transported to
sinks in xylem
Therefore have inverse gradient
with IAA
Why IAA/CK affects
development

91. Cytokinin Synthesis
Most cytokinins are made at root
apical meristem & transported to
sinks in xylem
Therefore have inverse gradient
with IAA
Why IAA/CK affects development
Rapidly metabolized by sink

92. Cytokinin Effects
Regulate cell division
Need mutants defective in CK metabolism or signaling to detect this in vivo

93. Cytokinin Effects
Regulate cell division
Need mutants defective in CK metabolism or signaling to detect this in vivo
SAM & plants are smaller when
[CK]

94. Cytokinin Effects
SAM & plants are smaller when [CK]
Roots are longer!

95. Cytokinin Effects
Usually roots have too much CK: inhibits division!
Cytokinins mainly root & shoot meristems