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Growth regulators Auxins Cytokinins Gibberellins Abscisic acid Ethylene Brassinosteroids

Growth regulators Auxins Cytokinins Gibberellins Abscisic acid Ethylene Brassinosteroids Strigolactones All are small organics: made in one part, affect another part. Auxin First studied by Darwins! Showed that a "transmissible influence" made at tips caused bending lower down

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Growth regulators Auxins Cytokinins Gibberellins Abscisic acid Ethylene Brassinosteroids

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

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

  3. 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

  4. Auxin 1934: Indole-3-Acetic acid (IAA) from the urine of pregnant women was shown to cause bending IAA is the mainauxinin vivo. Others include Indole-3-butyric acid (IBA), 4-Chloroindole-3-acetic acid and phenylacetic acid (PA) IAA IBA PA 4-CI-IAA

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

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

  7. 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!

  8. 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- -> IAAH due to low pH Cycle repeats

  9. 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

  10. 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

  11. Auxin Action • Two models: • Acid growth: IAA starts H+ pumping that loosens cell wall

  12. Auxin Action • Two models: • Acid growth: IAA starts H+ pumping that loosens cell wall • Low pH is sufficient to cause elongation

  13. Auxin Action • Two models: • Acid growth: IAA starts H+ pumping that loosens cell wall • Low pH is sufficient to cause elongation • H+ pump activators cause elongation

  14. Auxin Action • Two models: • Acid growth: IAA starts H+ pumping that loosens cell wall • Gene activation

  15. Auxin Action • IAA activates cell elongation & transcription in targets

  16. Auxin Action IAA activates cell elongation & transcription in targets Elongation has lag of 10'

  17. Auxin Action IAA activates cell elongation & transcription in targets Elongation has lag of 10' IAA induces PM H+ pump with 10' lag

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

  19. Auxin Action • IAA 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

  20. Active transport • H+ pumps • lower pH in lysosomes, stomach

  21. Auxin Action • IAA 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

  22. Auxin Action • IAA 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'!

  23. Auxin Action • IAA 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'! • Some are light-regulated: induced in cotyledons & repressed in hypocotyls • Controlled by • PIFs

  24. Auxin Action Acid- growth: IAA-induced pH drop activates expansins & glucanases Phototropism is due to more elongation on shaded side

  25. Auxin Action Acid- growth: IAA-induced pH drop activates extensins & glucanases Phototropism is due to more elongation on shaded side due to lateral IAA redistribution

  26. Auxin Action Acid- growth: IAA-induced pH drop activates extensins & glucanases Phototropism is due to more elongation on shaded side due to lateral IAA redistribution IAA export blockers stop phototropism

  27. Auxin Action Phototropism is due to more elongation on shaded side due to lateral IAA redistribution IAA export blockers stop phototropism PIN1 goes away in cells on light side & PIN3 on cell sides takes over

  28. Auxin Action Phototropism is due to more elongation on shaded side due to lateral IAA redistribution IAA export blockers stop phototropism PIN1 goes away in cells on light side & PIN3 on cell sides takes over IAA moves sideways

  29. Auxin Action Phototropism is due to more elongation on shaded side due to lateral IAA redistribution IAA export blockers stop phototropism PIN1 goes away in cells on light side & PIN3 on cell sides takes over IAA moves sideways Lower pH on shaded side enhances IAA uptake

  30. Auxin Action Gravitropism Shoots bend up!

  31. Auxin Action • Gravitropism • Shoots bend up! • Roots bend down!

  32. Auxin Action • Gravitropism • Shoots bend up! • Roots bend down! • Both effects are due to IAA redistribution to lower side!

  33. Auxin Action • Gravitropism • Shoots bend up, Roots bend down • Both effects are due to IAA • redistribution to lower side! • [IAA] stimulates shoots • & inhibits roots!

  34. Apical dominance • Auxin inhibits lateral bud formation • decapitate plant and lateral buds develop

  35. Apical dominance • Auxin inhibits lateral bud formation • decapitate plant and lateral buds develop • apply IAA to cut tip & lateral buds do not develop

  36. Apical dominance • Auxin induces lateral & adventitious roots

  37. Apical dominance • Auxin induces lateral & adventitious roots • Promotes cell division at initiation site

  38. Apical dominance • Auxin induces lateral & adventitious roots • Promotes cell division at initiation site • Promotes cell elongation & viability as root grows

  39. Auxin signaling Used "auxin-resistant" mutants to find genes involved in auxin signaling

  40. Auxin signaling Used "auxin-resistant" mutants to find genes involved in auxin signaling Many are involved in selective protein degradation!

  41. Auxin signaling Used "auxin-resistant" mutants to find genes involved in auxin signaling Many are involved in selective protein degradation! Some auxin receptors, eg TIR1 are E3 ubiquitin ligases!

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

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

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

  45. Auxin signaling • ABP1 is a different IAA receptor localized in ER • Activates PM H+ pump by sending it to PM & keeping it there

  46. Auxin signaling • ABP1 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!

  47. Auxin & other growth regulators • ABP1 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?

  48. 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

  49. Cytokinins Discovered as factors which induce cultured cells to divide Haberlandt (1913): phloem chemical stimulates division

  50. Cytokinins Discovered as factors which induce cultured cells to divide Haberlandt (1913): phloem chemical stimulates division van Overbeek (1941): coconut milk stimulates division

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