1. Runners/walkers needed for “Relay for Heat “ on Saturday
Continues all day
Run/walk when you feel like it
Help needed for Chester Street Elementary School's STEAM Day
Science stuff with 1st – 5th graders
10-3:30 on Friday March 29
Help needed for dissecting frogs with 7th graders on Friday April 5
8:30- 10:30 in CSC223

2. Plant defense responses Hypersensitive response
Prepare a 10’ talk for Friday March 22 on plant defenses or describe interactions between plants & pathogens, pests or symbionts
Plant defense responses
Hypersensitive response
Systemic acquired resistance
Innate immunity
Phytoalexins
Defensins
Oxidative burst
Some possible pests
Nematodes
Rootworms
Aphids
Thrips
Gypsy moths
hemlock woolly adelgid
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
Burkholderia ambifaria

3. 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!

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 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

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

7. 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!

8. 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!

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

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

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

12. 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

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

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

15. 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

16. 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

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

18. 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

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

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

21. 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 -

22. 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 -

23. 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 -

24. 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

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

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

27. 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

28. 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!

29. 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!

30. 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

31. 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

32. 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

33. 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

34. 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

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

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

37. 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

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

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

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

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

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

43. 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

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

45. 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

46. 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'!

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

48. 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

49. 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

50. 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

51. 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

52. 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

53. Auxin Action
Gravitropism
Shoots bend up!

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

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

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

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

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

59. Apical dominance
Auxin induces lateral & adventitious roots

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

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

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

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

64. 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!

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

66. 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"

67. 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

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

69. 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!

70. 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?

71. 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