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Biol 352 Lecture 8 Ethylene: The Gaseous Hormone January 31, 2007

Biol 352 Lecture 8 Ethylene: The Gaseous Hormone January 31, 2007. http://www.mccullagh.org/image/10d-7/carnation-flower.html. Review: Cytokinins Cytokinins are N 6 -substituted aminopurines that initiate cell proliferation together with auxin.

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Biol 352 Lecture 8 Ethylene: The Gaseous Hormone January 31, 2007

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  1. Biol 352 Lecture 8 Ethylene: The Gaseous Hormone January 31, 2007 http://www.mccullagh.org/image/10d-7/carnation-flower.html

  2. Review:Cytokinins • Cytokinins are N6-substituted aminopurines that initiate cell proliferation together with auxin. • Zeatin is the most abundant natural cytokinin. • 1st committed step in cytokinin biosynthesis is catalyzed by isopentenyl transferase (IPT) • Cytokinin oxidase degrades cytokinin • Cytokinin regulates cell division, morphogenesis, cell enlargement, senescence • Phosphorelay two-component signalling system in cytokinin signal transduction

  3. Lecture Outline: • Structure of ethylene • Biosynthesis of ethylene • Function of ethylene • Ethylene signal transduction • Summary

  4. Learning Objectives: • Determine the biosynthetic origin of ethylene • Define key enzymes in ethylene biosynthesis • Describe the action of ethylene in triple response and abscission • Distinguish climacteric and non-climacteric fruits • Establish the concept ofethylene signal transduction • Reading: • 4th Ed, Plant Physiology, Taiz & Zeiger, Chapter 22: p571-590 • (3rd Ed, Plant Physiology, Taiz & Zeiger, Chapter 22: p519-537)

  5. H H C C H H • Ethylene: • Is the only gaseous plant hormone • Is the only member of its class • Has the simplest structure • Functional features: fruit ripening, triple response

  6. Ethylene Biosynthesis

  7. Ethylene Biosynthesis: • Ethylene can be produced by almost all parts of higher plants. • Senescing tissues and ripening fruits produce more ethylene than young or mature tissues • Amino acid METHIONINE is the precursor of ethylene

  8. Ethylene Biosynthesis: • Immediate precursor: 1-aminocyclopropane-1-carboxylic acid (ACC) • Oxygen is required for the conversion from ACC to ethylene • Key enzyme: ACC synthase, ACC oxidase • Rate-limiting step: catalyzed by ACC synthase

  9. Ethylene Biosynthesis: 5) Biosynthesis inhibitor: i) AOA (aminooxyacetic acid) ii) AVG (aminoethoxy-vinyl-glycine 6) Action inhibitors: i) Silver ions (Ag+): ii) MCP 7) Biosynthesis enhancers: Fruitripening auxin flower senescence wounding drought stress

  10. Functions of Ethylene • Fruit ripening • Triple response • Abscission • Senescence • Root hair formation • Leaf epinasty • Seed germination

  11. 1. Ethylene Induces Ripening of Climacteric Fruits Climacteric fruits: Fruits that ripen in response to ethylene exhibit a characteristic respiratory rise before the ripening phase. Such fruits show a spike of ethylene production immediately before the respiratory rise. Apple, banana, peach, pear, tomato Nonclimacteric fruits: Fruits that do not exhibit the respiration and ethylene production rise. Cherry, grape, citrus, pineapple Autocatalytic effect: Ethylene induces the fruit to produce additional ethylene

  12. 2.Ethylene Induces Triple Response • Triple Response (pea): • Reduced stem elongation • Increased lateral growth (swelling) • Abnormal, horizontal growth

  13. 2.Ethylene Induces Triple Response Mutant Wild type • Triple response (Arabidopsis): • Inhibition and swelling of hypocotyl • Inhibition of root elongation • Exaggeration of the apical hook

  14. 3. Ethylene Promotes Abscission Left: wild type Right: expression of, a mutated version of ethylene receptor ETR1-1

  15. 3. Ethylene Promotes Abscission • Abscission: shedding of leaves, fruits, flowers, and other plant organs • Abscission layers: the specific layers of cells where abscission takes place • Mechanism: Cell wall breakdown because of an increase in cell wall-hydrolyzing enzymes

  16. Senescence Epinasty Root hair

  17. Ethylene Signal Transduction • Two important classes of mutants: • Ethylene-resistant or ethylene-insensitive mutants: Mutants that fail to responses to exogenous ethylene • Constitutive mutants: Mutants that display the response even in the absence of ethylene

  18. etr1 mutant: ethylene resistant 1 + ethylene

  19. ctr1 mutant: constitutive triple response 1

  20. Ethylene Receptors Two-component histidine kinase signalling system

  21. Cytokinin Signal Transduction

  22. Model of Ethylene Signalling

  23. Ethylene Receptors Concept:Functional redundant Disruption of any single gene in a given gene family results no effect, but a plant with disruptions in all genes in a given gene family exhibits phenotypes

  24. Model of Ethylene Signalling • Two-component histidine kinase signalling system. • Receptors are located on the endoplasmic reticulum (ER).

  25. Summary: • Ethylene is a gaseous plant hormone. • Precursor: amino acid methionine; immediate precursor: ACC. • Key enzymes for biosynthesis: ACC synthase, ACC oxidase. • Ethylene functions: fruit ripening, triple response, abscission, flower senescence, root hair development, etc. • Two-component signalling system in ethylene signal transduction.

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