Growth regulators
1.Auxins
2.Cytokinins
3.Gibberellins
4.Abscisic acid
5.Ethylene
6.Brassinosteroids
All are small
organics: made in
one part, affect
another part
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!
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] = assay
1934: Indole-3-Acetic acid (IAA) from the urine of
pregnant women was shown to cause bending
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
4-CI-IAA
IBA
PA
Auxin
IAA is the main auxin in vivo.
Many synthetic auxins have been identified
IAA
Auxin
IAA is the main auxin in vivo.
Many synthetic auxins have been identified
No obvious structural similarity, yet all work!
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
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
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
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
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
Auxin
IAA
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.
Auxin
IAA
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.
Auxin
>90%of IAA is conjugated to sugars in vivo!
Auxin
>90%of IAA is conjugated to sugars in vivo!
Inactive, but readily activated!
Auxin
>90%of IAA is conjugated to sugars in vivo!
Inactive, but readily activated!
Best way to measure [auxin] is bioassay!
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
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!
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!
Auxin Synthesis
Made in leaves & transported to roots so [IAA] decreases going
down the plant
Most is made from trp
Auxin Synthesis
Most is made from trp
Also made by trp-independent pathway: exits before trp
Auxin Synthesis
Most is made from trp
Also made by trp-independent pathway: exits before trp
Path used varies
between tissues
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
Auxin Levels
No way to run out of IAA! [IAA] depends on metabolism
Auxin Levels
No way to run out of IAA!
[IAA] depends on metabolism
Most cells are IAA sinks!
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
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
Auxin Transport
IAA transport therefore affects growth & development
is polar and basipetal: New roots form at base of stem even if stored
upside-down
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