Growth regulators1.Auxins2.Cytokinins3.Gibberellins4.Abscisic acid5.Ethylene6.BrassinosteroidsAll are small organics: made inone part, affectanother part

Growth regulatorsAll are small organics: made in one part, affect another partTreating a plant tissue with a hormone is like putting a dime in a vending machine. It depends on the machine, not the dime!

Auxin1919: Paal showed that if tip was replaced asymmetrically, plant grew asymmetrically even in darkUneven amounts of "transmissible influence" makes bend1926: Went showed that a chemical that diffused from tips into blocks caused growthIf placed asymmetrically get bending due to asymmetrical growthAmount of bending depends on [auxin] = assay1934: Indole-3-Acetic acid (IAA) from the urine of pregnant women was shown to cause bending

Auxin1934: Indole-3-Acetic acid (IAA) from the urine of pregnant women was shown to cause bendingIAA is the main auxin in vivo.Others include Indole-3-butyric acid (IBA), 4-Chloroindole-3-acetic acid and phenylacetic acid (PA)

IBAIBA

PAPA4-CI-IAA

IAAIAA

AuxinIAA is the main auxin in vivo.Many synthetic auxins have been identified

IAAIAA

AuxinIAA is the main auxin in vivo.Many synthetic auxins have been identifiedNo obvious structural similarity, yet all work!

IAAIAA

AuxinIAA is the main auxin in vivo.Many synthetic auxins have been identifiedNo obvious structural similarity, yet all work!Widely used in agriculture

IAAIAA

AuxinIAA is the main auxin in vivo.Many synthetic auxins have been identifiedNo obvious structural similarity, yet all work!Widely used in agriculture • to promote growth (flowering, cuttings)

IAAIAA

AuxinIAA is the main auxin in vivo.Many synthetic auxins have been identifiedNo 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

IAAIAA

Auxinweed killers!

Agent orange was 1:1 2,4-D and 2,4,5-T

2,4,5-T was contaminatedwith dioxin, a carcinogen

IAAIAA

Auxinweed killers!

Agent orange was 1:1 2,4-D and 2,4,5-T

2,4,5-T was contaminatedwith dioxin, a carcinogen2,4-D is still widely used:selectively kills dicots

IAAIAA

Auxinweed killers!2,4-D is still widely used: selectively kills dicotsControls weeds in monocot crops (corn, rice, wheat)Mech unclear: may cause excess ethylene or ABA production.

IAAIAA

Auxinweed killers!2,4-D is still widely used: selectively kills dicotsControls weeds in monocot crops (corn, rice, wheat)Mech unclear: may cause excess ethylene or ABA production.

IAAIAA

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 tissuesRoots are much more sensitive than leaves!

AuxinCritical concentration varies between tissuesRoots are much more sensitive than leaves!Made in leaves & transported to roots so [IAA] decreases going down the plantMost cells are IAA sinks!

Auxin SynthesisMade in leaves & transported to roots so [IAA] decreases going down the plantMost is made from trp

Auxin SynthesisMost is made from trpAlso made by trp-independent pathway: exits before trp

Auxin SynthesisMost is made from trpAlso made by trp-independent pathway: exits before trpPath used variesbetween tissues

Auxin SynthesisMost is made from trpAlso made by trp-independent pathway: exits before trpPath used variesbetween tissuesNo way to runout of IAA

Auxin LevelsNo way to run out of IAA! [IAA] depends on metabolism

Auxin LevelsNo way to run out of IAA! [IAA] depends on metabolismMost cells are IAA sinks!

Auxin LevelsNo way to run out of IAA! [IAA] depends on metabolismMost cells are IAA sinks! IAA is made at shoot apex & transported down: basipetal

Auxin LevelsNo way to run out of IAA! [IAA] depends on metabolismMost cells are IAA sinks! IAA is made at shoot apex & transported down: basipetalIAA transport therefore affectsgrowth & development

Auxin TransportIAA transport therefore affects growth & developmentis polar and basipetal: New roots form at base of stem even if stored upside-down

Auxin TransportIAA transport therefore affects development: is polar and basipetal. New roots form at base of stem even if stored upside-down.Stem sectionsonly move IAA basipetally