1. Plant Growth
Size & shape depends on cell # & cell size
Decide when,where and which way to divide

2. Plant Growth
Size & shape depends on cell # & cell size
Decide which way to divide & which way to elongate
Periclinal = perpendicular to surface: get longer
Anticlinal = parallel to surface: add more layers
Now must decide which way to elongate: which walls to stretch

3. Plant Cell Walls and Growth
1˚ wall made first
mainly cellulose
Can stretch! Control elongation by controlling orientation of cell wall fibers as wall is made
1˚ walls = 25% cellulose, 25% hemicellulose, 35% pectin, 5% protein (but highly variable)

4. Plant Cell Wall Proteins
HRGP: hydroxyproline-rich glycoproteins (eg extensin)
PRP: proline-rich proteins
3. GRP: Glycine-rich proteins
4. Arabinogalactan proteins
Highly glycosylated: helps bind CH2O
Anchored to PM by GPI
Help cell adhesion and cell signaling
5. Also many enzymes involved in cell wall synthesis and loosening

5. Plant Cell Walls and Growth
Lignins = polyphenolic macromolecules: 2nd most abundant on earth (after cellulose)
Bond hemicellulose: solidify & protect cell wall (nature’s cement): very difficult to digest
Monomers are made in cytoplasm & secreted

6. Plant Cell Walls and Growth
Peroxidase & laccase in cell wall create radicals that polymerise non-enzymatically
Very difficult to digest, yet major plant component!

7. Plant Cell Walls and Growth
Elongation: loosening the bonds joining the cell wall
Can’t loosen too much or cell will burst
Must coordinate with cell wall synthesis so wall stays same
Must weaken crosslinks joining cellulose fibers
Turgor then drives expansion

8. Plant Cell Walls and Growth
Expansins loosen bonds between
Hemicellulose & cellulose
Endoglucanases & transglucanases
cut & reorganize hemicellulose & pectin
XET is best-known
Cuts & rejoins hemicellulose
in new ways
Expansins, endoglucanases &
transglucanases catalyse cell
wall creepage
Activated by low pH

9. Plant Cell Walls and Signaling
Pathogens must digest cell wall to enter plant
Release cell wall fragments
Many oligosaccharides signal”HELP!”
Elicit plant defense responses

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

11. 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!

12. Auxin
First studied by Darwins!
Showed that a "transmissible influence" made at tips caused bending lower down

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

14. Auxin
First studied by Darwins!
Showed that a "transmissible influence" made at tips caused bending lower down
No tip, no curve!
1913:Boysen-Jensen showed that diffused through agar blocks but not through mica

15. Auxin
1913:Boysen-Jensen showed that diffused through agar blocks but not through mica
1919: Paal showed that if tip was replaced asymmetrically, plant grew asymmetrically even in dark

16. Auxin
1913:Boysen-Jensen showed that diffused through agar blocks but not through mica
1919: Paal showed that if tip was replaced asymmetrically, plant grew asymmetrically even in dark
Uneven amounts of "transmissible influence" makes bend

17. 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

18. 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

19. 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]

20. 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

21. 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

22. IAA Auxin IAA is the main auxin in vivo.
Many synthetic auxins have been identified
IAA

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

24. 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
IAA

25. 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

26. 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

27. 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

28. 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

29. 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

30. 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

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

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

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

34. 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

35. 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!

36. 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!

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

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

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

40. 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

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

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

43. 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

44. 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

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

46. 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

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

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

49. 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 -

50. 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 -

51. 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 -

52. 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

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

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

55. 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

56. 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!

57. 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!

58. 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

59. 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

60. 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

61. 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

62. 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