1. Plant defense responses Hypersensitive response
Prepare a 10’talk for Friday Feb 27 on plant defense responses or describe interactions between plants & pathogens or symbionts
Plant defense responses
Hypersensitive response
Systemic acquired resistance
Innate immunity
Phytoalexin synthesis
Defensins and other proteins
Oxidative burst
Some possible pathogens
Agrobacterium tumefaciens
Agrobacterium rhizogenes
Pseudomonas syringeae
Pseudomonas aeruginosa
Viroids
DNA viruses
RNA viruses
Fungi
Oomycetes
Some possible symbionts
N-fixing bacteria
N-fixing cyanobacteria
Endomycorrhizae
Ectomycorrhizae

2. Growth regulators
Auxins
Cytokinins
Gibberellins
Abscisic acid
Ethylene
Brassinosteroids
All are small
organics: made in
one part, affect
another part

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

4. 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

5. IAA IBA 4-CI-IAA PA Auxin
1934: Indole-3-Acetic acid (IAA) from the urine of pregnant women was shown to cause bending
IAA is the main auxin in vivo.
Others include Indole-3-butyric acid (IBA), 4-Chloroindole-3-acetic acid and phenylacetic acid (PA)
IAA
IBA
4-CI-IAA PA

6. 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)
as weed killers!
Agent orange was 1:1
2,4-D and 2,4,5-T
IAA

7. 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, a carcinogen
IAA

8. 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, a carcinogen
2,4-D is still widely used:
selectively kills dicots
IAA

9. Auxin
weed killers!
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

10. Auxin
weed killers!
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

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

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

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

14. 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

15. 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!

16. 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!

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

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

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

20. 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

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

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

23. 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

24. 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

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

26. 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

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

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

29. 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 -

30. 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 -

31. 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 -

32. 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

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

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

35. 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

36. 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!

37. 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!

38. 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

39. 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

40. 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

41. 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

42. 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

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

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

45. 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

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

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

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

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

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

51. 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

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

53. 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

54. 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'!

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

56. 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

57. 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

58. 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

59. 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

60. 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

61. Auxin Action
Gravitropism
Shoots bend up!

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

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

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

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

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

67. Apical dominance
Auxin induces lateral & adventitious roots

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

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

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

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

72. 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!

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

74. 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"

75. 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

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

77. 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!

78. 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?

79. 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