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

2. 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

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

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

5. 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 -

6. 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 -

7. 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 -

8. 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

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

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

11. 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

12. 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!

13. 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!

14. 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

15. 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

16. 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

17. 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

18. 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

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

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

21. 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

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

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

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

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

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

27. 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

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

29. 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

30. 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'!

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

32. 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

33. 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

34. 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

35. 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

36. 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

37. Auxin Action
Gravitropism
Shoots bend up!

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

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

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

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

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

43. Apical dominance
Auxin induces lateral & adventitious roots

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

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

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

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

48. 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!

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

50. 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"

51. 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

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

53. 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!

54. 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?

55. 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