Help needed for Chester Street Elementary School's STEAM Day Science stuff with 1st – 5th graders 10-3:30 on Friday March 29 Help needed for dissecting frogs with 7th graders on Friday April 5 8:30- 10:30 in CSC223

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 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

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- -> Cycle repeats

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

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

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

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

Apical dominance Auxin induces lateral & adventitious roots

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

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"

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

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!

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

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

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

Cytokinins Discovered as factors which induce cultured cells to divide Haberlandt (1913): phloem chemical stimulates division van Overbeek (1941): coconut milk stimulates division Miller… Skoog (1955): degraded DNA stimulates division!

Cytokinins Discovered as factors which induce cultured cells to divide Haberlandt (1913): phloem chemical stimulates division van Overbeek (1941): coconut milk stimulates division Miller… Skoog (1955): degraded DNA stimulates division! Kinetin was the breakdown product

Cytokinins Discovered as factors which induce cultured cells to divide Haberlandt (1913): phloem chemical stimulates division van Overbeek (1941): coconut milk stimulates division Miller… Skoog (1955): degraded DNA stimulates division! Kinetin was the breakdown product Derived from adenine

Cytokinins Discovered as factors which induce cultured cells to divide Haberlandt (1913): phloem chemical stimulates division van Overbeek (1941): coconut milk stimulates division Miller… Skoog (1955): degraded DNA stimulates division! Kinetin was the breakdown product Derived from adenine Requires auxin to stimulate division

Cytokinins Requires auxin to stimulate division Kinetin/auxin determines tissue formed (original fig)

Cytokinins Requires auxin to stimulate division Kinetin/auxin determines tissue formed Inspired search for natural cytokinins Miller& Letham (1961) ± simultaneously found zeatin in corn Kinetin trans- Zeatin

Cytokinins Miller& Letham (1961) ± simultaneously found zeatin Later found in many spp including coconut milk Kinetin trans-Zeatin

Cytokinins Miller& Letham (1961) ± simultaneously found zeatin Later found in many spp including coconut milk Trans form is more active, but both exist (& work) Many other natural & synthetics have been identified

Cytokinins Many other natural & synthetics have been identified Like auxins, many are bound to sugars or nucleotides

Cytokinins Many other natural & synthetics have been identified Like auxins, many are bound to sugars or nucleotides Inactive, but easily converted

Cytokinin Synthesis Most cytokinins are made at root apical meristem & transported to sinks in xylem

Cytokinin Synthesis Most cytokinins are made at root apical meristem & transported to sinks in xylem Therefore have inverse gradient with IAA

Cytokinin Synthesis Most cytokinins are made at root apical meristem & transported to sinks in xylem Therefore have inverse gradient with IAA Why IAA/CK affects development

Cytokinin Synthesis Most cytokinins are made at root apical meristem & transported to sinks in xylem Therefore have inverse gradient with IAA Why IAA/CK affects development Rapidly metabolized by sink

Cytokinin Effects Regulate cell division Need mutants defective in CK metabolism or signaling to detect this in vivo

Cytokinin Effects Regulate cell division Need mutants defective in CK metabolism or signaling to detect this in vivo SAM & plants are smaller when [CK]

Cytokinin Effects SAM & plants are smaller when [CK] Roots are longer!

Cytokinin Effects Usually roots have too much CK: inhibits division! Cytokinins mainly act @ root & shoot meristems

Cytokinin Effects Cytokinins mainly act @ root & shoot meristems Control G1-> S & G2-> M transition

Cytokinin Effects Promote lateral bud growth

Cytokinin Effects Promote lateral bud growth Delay leaf senescence

Cytokinin Effects Promote lateral bud growth Delay leaf senescence Promote cp development, even in dark

Cytokinin Receptors Receptors were identified by mutation Resemble bacterial 2-component signaling systems

Cytokinin Action 1.Cytokinin binds receptor's extracellular domain

Cytokinin Action 1.Cytokinin binds receptor's extracellular domain 2. Activated protein kinases His kinase & receiver domains

Cytokinin Action 1.Cytokinin binds receptor's extracellular domain 2. Activated protein kinases His kinase & receiver domains 3. Receiver kinases His-P transfer relay protein (AHP)

Cytokinin Action 1.Cytokinin binds receptor's extracellular domain 2. Activated protein kinases His kinase & receiver domains 3. Receiver kinases His-P transfer relay protein (AHP) 4. AHP-P enters nucleus & kinases ARR response regulators

Cytokinin Action 4. AHP-P enters nucleus & kinases ARR response regulators 5. Type B ARR induce type A

Cytokinin Action 4. AHP-P enters nucleus & kinases ARR response regulators 5. Type B ARR induce type A 6. Type A create cytokinin responses

Cytokinin Action 4. AHP-P enters nucleus & kinases ARR response regulators 5. Type B ARR induce type A 6. Type A create cytokinin responses 7. Most other effectors are unknown but D cyclins is one effect.

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 Auxin induces Gibberellins