Lecture 5 plant hormones 2014
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Plant hormones regulate growth and development in response to environmental and biological signals. The major plant hormones are auxin, cytokinin, abscisic acid, jasmonic acid, gibberellic acid, ethylene, and brassinosteroids. These hormones function through complex signaling cascades in the cell involving gene transcription and protein degradation. Hormone manipulation is important for tissue culture and seed germination.
Lecture 5 plant hormones 2014
- 1. Lecture 5 Plant hormones and Signal transduction PLSC 452/552 1/23/14 Department of Plant Sciences Neal Stewart Lab
- 2. Brain teaser • Little Johnny nails a sign 90 cm off the ground to a tree outside of his clubhouse that says “no girls allowed.” If the tree grows 12 cm every year, at what height will the sign be when Little Johnny returns as Big Johnny in 15 years?
- 3. Overview • Define “hormone” as a functional compound. What is the function and importance of hormones? • Know the major plant hormones • Understand real-world application of hormones • Importance of hormones for tissue culture: introduction
- 4. What is a hormone? • Biochemical which regulates growth based on biological and environmental influences • Synonyms: Plant hormones, plant growth regulators (PGRs), phytohormones • Regulate growth and development • Mobile throughout plant • Environment and stress responsive
- 5. Major plant hormones • Auxin – Greek: auxein; to grow or increase • Cytokinin – cytokinesis (cell division) • Abscisic acid – abscission • Jasmonic acid – found in jasmine oil • Gibberellic acid – pathogen Gibberella • Ethylene – chemical brother to ethanol • Brassinosteroids – derived from Brassica spp.
- 6. Finding plant hormones Observational: Darwin stumbles on auxin – Noticed grass tips grow toward light – With tip growth responded to light – Without tip growth had no response Mutation screening: (aka forward genetics) – Dwarf plants are can be hormone deficient
- 7. ABRC teaching tools website
- 8. General hormone biochemistry • Present in all cells at various levels • Classes of hormones work in signal cascades – Hormone-receptor interactions – Respond to a host of factors and biological needs • Abiotic – Water stress – Light – Nutrient deficiency • Biotic – Growth – Development – Herbivore stress
- 9. Hormone biosynthesis Made from four biosynthetic pathways: – Terpenoids • AMP + IPP (cytokinins) • Carotenoid breakdown (abscisic acid) • Diterpene (gibberellic acid) • Triterpene (brassinosteroids) – Fatty acids (jasmonic acid) – Tryptophan (auxins) – Methionine (ethylene)
- 11. Auxins • Greek: auxein; to grow or increase • Apical dominance growth • Cell elongation • Hormone level very important 2, 4-dichlorophenoxyacetic Acid http://pubchem.ncbi.nlm.nih.gov/
- 13. Taiz and Zeiger. 2002. Plant Physiology, 3rd Ed.
- 15. Cytokinin • Cytokinesis (cell division) • Accidently added degraded DNA to medium • Organization and development of xylem tissue • Response to light • Lateral growth of shoots • Open stomata http://pubchem.ncbi.nlm.nih.gov/ Kinetin
- 16. Application: cotton spraying • Adding cytokinins to young cotton increase drought- resistance • Arizona – 31% US cotton, highest yield acre-1
- 17. Auxin and cytokinin ratio importance • Auxin alone = Large cells (no division) • Cytokinin alone = Cells have no change • Auxin + Cytokinin = Normal cell growth and division • Auxin + >Cytokinin = Shoot growth • >Auxin = Cytokinin = Root growth
- 18. Auxin Cytokinin http://users.ugent.be/~p debergh/pri/pri4ez04.jpg
- 19. Abscisic acid (ABA) • Originally implicated in leaf and fruit abscission • Involved in leaf senescence • Maintains seed dormancy (opposed to GA) • Involved in stomata regulation (closes) • Single hormone unit http://pubchem.ncbi.nlm.nih.gov/
- 21. Jasmonic acid • First identified in jasmine oil • Response to biotic stress – Wounding induces JA biosynthesis – Microbial and fungal invasion • Plant growth effects similar to auxin – Specialty growth structures http://pubchem.ncbi.nlm.nih.gov/
- 22. Jasmonic acid: Plant-insect co-evolution Tri-trophic interactions Degenhardt(2009) Plant Physiology 149:96-102
- 24. Gibberellic acid • Originally found in Gibberella (rice pathogen) – Responsible for ‘foolish seedling’ phenomenon – Uninhibited growth until breaking • Involved in cell elongation • Flowering and seed germination http://pubchem.ncbi.nlm.nih.gov/
- 25. Modification of GA in rice Miyako Ueguchi-Tanaka 2005 Nature 437, 693-698
- 26. Spraying GA for increased fruit yield GA induces fruiting in absence of seed http://www.extension.org/pages/31607/using-plant-growth-regulators-to- increase-the-size-of-table-grape-berries#.Ut9EYbROmM8
- 27. Ethylene: the cell phone of PGRs • A hydrocarbon gas • Involved in fruit ripening, stress response • Inhibition of growth in dark conditions • Excess ethylene inhibits callus growth
- 28. Conversational Plants? • Ethylene production increases during stress – Drought – Heat • Perceived by neighboring plants • Unstressed plants induce stress pathways
- 29. Brassinosteroids • Stress responses – Switchgrass suspension cells have minor amounts of lignin (small amounts of H monolignols) – Addition of brassinolide induces normal lignin formation and composition • Stem elongation • Seed germination • Pollen tube growth • Cell differentiation control Brassinolide http://pubchem.ncbi.nlm.nih.gov/
- 30. Brassinosteroid mutant Bishopp A et al. Development 2006;133:1857-1869 Overview of hormone mutants Ethylene mutant grown in dark Cytokinin mutant Cytokinin mutant closer look Abscisic acid mutant
- 31. Hormones (PGR) pathways • PGRs work in complex cascades to produce signals – Synergistic – Anatognistic • Variety of actions in cell – Gene transcription – Protein degradation http://chriscarterart.wordpress.com/2010/05/09/m others-day-2/mikado-plant-watercolor-sketch-chris- carter-050910/
- 33. http://molbio.mgh.harvard.edu/sheenweb/cytokinin_signaling.html Arabidopsis histidine kinase sensing and signaling; 2) A histidine phosphotransferase protein nuclear translocation; 3) A response regulation transcription activation; and 4) a negative feedback loop through cytokinin- inducible ARR gene products.
- 34. Introduction: the importance of manipulation of hormones for tissue culture • Auxins and cytokinins are very important – Higher auxin induces root growth – Equal ratio induces callus and cell enlargement – Lower auxin induces shoot growth • Gibberellic acid germinates difficult seeds • Add brassinosteroids for cell wall induction
- 35. Lecture summary • Hormones are biochemicals that regulate plant growth based on biological and environmental cues • Auxin and cytokinin are key for plant growth • Abiotic and biotic stress response is regulated by hormones • Cell signaling is regulated by specific receptors on cell membranes
Editor's Notes
- #31: Phenotypes associated with the brassinosteroid, ethylene, cytokinin and abscisic acid receptor mutants. All images are shown against wild type for comparison. (A) The brassinosteroid receptor mutant bri1-301 (bottom) shows a dwarf phenotype. (B) The dark-grown ethylene receptor mutant ein4 (right) lacks the triple response (left; see main text). (C) The triple cytokinin receptor mutant cre1 ahk2 ahk3 (right) shows reduced growth. (D) The root vascular bundle normally consists of xylem, phloem and procambium cell files, whereas in wol (bottom), or in cre1 ahk2 ahk3 (not shown), there are fewer vascular cell lineages, all of which differentiate as protoxylem. The vascular bundle is encircled by a layer of pericycle cells (asterisks) (E) The abscisic acid receptor mutant fca (right) flowers later than wild type, as demonstrated by increased leaf number at flowering. Scale bars: in C, 2 mm; in D, 10 μm. [A is reprinted, with permission, from Cano-Delgado et al. (Cano-Delgado et al., 2004); B is reprinted, with permission, from Hua et al. (Hua et al., 1998); E is reprinted, with permission, from Amasino (Amasino, 2003).]