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

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

Chemiosmotic Auxin Transport1. Apoplastic IAAH diffuses into cell• IAAH due to low pH

Chemiosmotic Auxin Transport1. Apoplastic IAAH diffuses into cell• IAAH due to low pH• AUX1 pumps in IAA-

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Chemiosmotic Auxin Transport1. Apoplastic IAAH diffuses into cell• IAAH due to low pH• AUX1 pumps in IAA-2. In cell IAAH-> IAA- due to pH 7.2

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Chemiosmotic Auxin Transport1. 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

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Chemiosmotic Auxin Transport1. 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 IAAH3. IAA- is pumped out by PIN proteins in basal part of cell

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Chemiosmotic Auxin Transport1. 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 IAAH3. IAA- is pumped out by PIN proteins in basal part of cell4. In apoplast IAA- -> IAAH due to low pHCycle repeats

Chemiosmotic Auxin TransportSupporting evidence1. Some chemicals specifically block import or export

Chemiosmotic Auxin TransportSupporting evidence1.Some chemicals specifically block import or export• Export blockers stop efflux into block, no effect on uptake

Chemiosmotic Auxin TransportSupporting evidence1.Some chemicals specifically block import or export• Export blockers stop efflux into block, no effect on uptake• Import blockers stop uptake

Chemiosmotic Auxin TransportSupporting evidence1.Some chemicals specifically block import or export• Export blockers stop efflux , no effect on uptake• Import blockers stop uptake• Both mess up development!

Chemiosmotic Auxin TransportSupporting evidence1.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!

Chemiosmotic Auxin TransportSupporting evidence1.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

Chemiosmotic Auxin TransportSupporting evidence1.Some chemicals specifically block import or export• Both mess up development!2.AUX1 encodes an IAA-H+ symporter found at top of cell

Chemiosmotic Auxin TransportSupporting evidence1.Some chemicals specifically block import or export• Both mess up development!2.AUX1 encodes an IAA-H+ symporter found at top of cellaux1 resemble plants treated withimport blockers

Chemiosmotic Auxin TransportSupporting evidence1.Some chemicals specifically block import or export2.AUX1 encodes an IAA-H+ symporter found at top of cell• aux1 resemble plants treated with import blockers3. PINs encode IAAexporters found at cell base

Chemiosmotic Auxin TransportSupporting evidence1.Some chemicals specifically block import or export2.AUX1 encodes an IAA-H+ symporter found at top of cell• aux1 resemble plants treated with import blockers3. PINs encode IAAexporters found at cell base• pin1 resemble plants treatedwith export blockers

Auxin ActionTwo models:1.Acid growth: IAA starts H+

pumping that loosens cell wall

Auxin ActionTwo models:1.Acid growth: IAA starts H+

pumping that loosens cell wall• Low pH is sufficient to cause

elongation

Auxin ActionTwo models:1.Acid growth: IAA starts H+

pumping that loosens cell wall• Low pH is sufficient to cause

elongation• H+ pump activators cause

elongation

Auxin ActionTwo models:1.Acid growth: IAA starts H+

pumping that loosens cell wall2.Gene activation

Auxin ActionIAA activates cell elongation &

transcription in targets

Auxin ActionIAA activates cell elongation &

transcription in targetsElongation has lag of 10'

Auxin ActionIAA activates cell elongation & transcription in targetsElongation has lag of 10'IAA induces PM H+ pump with 10' lag

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

Auxin ActionIAA 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

Active transportH+ pumps

lower pH in lysosomes, stomach

Auxin ActionIAA 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

Auxin ActionIAA 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'!

Auxin ActionAcid- growth: IAA-induced pH drop activates expansins &

glucanasesPhototropism is due to more elongation on shaded side

Auxin ActionAcid- growth: IAA-induced pH drop activates extensins &

glucanasesPhototropism is due to more elongation on shaded side due to lateral

IAA redistribution

Auxin ActionAcid- growth: IAA-induced pH drop activates extensins & glucanasesPhototropism is due to more elongation on shaded side due to lateral IAA redistributionIAA export blockersstop phototropism

Auxin ActionPhototropism is due to more elongation on shaded side due to lateral IAA redistributionIAA export blockers stop phototropismPIN1 goes away in cells on light side & PIN3 on cell sides takes over

Auxin ActionPhototropism is due to more elongation on shaded side due to lateral IAA redistributionIAA export blockers stop phototropismPIN1 goes away in cells on light side & PIN3 on cell sides takes overIAA moves sideways

Auxin ActionPhototropism is due to more elongation on shaded side due to lateral IAA redistributionIAA export blockers stop phototropismPIN1 goes away in cells on light side & PIN3 on cell sides takes overIAA moves sideways Lower pH on shaded sideenhances IAA uptake

Auxin ActionGravitropismShoots bend up!

Auxin ActionGravitropism • Shoots bend up!• Roots bend down!

Auxin ActionGravitropism • Shoots bend up!• Roots bend down!Both effects are due to IAA redistribution to lower side!

Auxin ActionGravitropism• Shoots bend up, Roots bend downBoth effects are due to IAA redistribution to lower side! [IAA] stimulates shoots& inhibits roots!

Apical dominanceAuxin inhibits lateral bud formation• decapitate plant and lateral buds develop

Apical dominanceAuxin inhibits lateral bud formation• decapitate plant and lateral buds develop• apply IAA to cut tip & lateral buds do not develop

Apical dominanceAuxin induces lateral & adventitious roots

Apical dominanceAuxin induces lateral & adventitious roots• Promotes cell division at initiation site

Apical dominanceAuxin induces lateral & adventitious roots• Promotes cell division at initiation site• Promotes cell elongation & viability as root grows

Auxin signalingUsed "auxin-resistant" mutants to find genes involved in auxin signaling

Auxin signalingUsed "auxin-resistant" mutants to find genes involved in auxin signalingMany are involved in selective protein degradation!

Auxin signalingUsed "auxin-resistant" mutants to find genes involved in auxin signalingMany are involved in selective protein degradation!Some auxin receptors, eg TIR1 are E3 ubiquitin ligases!

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

Auxin signalingAuxin receptors eg TIR1 are E3 ubiquitin ligases!Upon binding auxin they activate complexes targeting AUX/IAA proteins for degradation!AUX/IAA inhibit ARFtranscription factors,so this turns on "early genes"

Auxin signalingAuxin receptors eg TIR1 are E3 ubiquitin ligases!Upon binding auxin they activate complexes targeting AUX/IAA proteins for degradation!AUX/IAA inhibit ARFtranscription factors,so this turns on "early genes"Some early genes turn on'late genes" needed for development

Auxin signalingABP1 is a different IAA receptor localized in ER•Activates PM H+ pump by sending it to PM & keeping it there

Auxin signalingABP1 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!

Auxin & other growth regulatorsABP1 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?

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