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• 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• 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 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
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 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• apply IAA to cut tip & lateral buds do not develop
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 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?