Lecture 5 Plant hormones and Signal transduction

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Lecture 5Plant hormonesandSignal transduction
PLSC 452/552 1/23/14 Department of Plant
Sciences Neal Stewart Lab
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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?

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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

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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

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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.

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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

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ABRC teaching tools website
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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

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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)

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KEGG database http//www.genome.jp/kegg/
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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/
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http//www.nsf.gov/news/news_images.jsp?cntn_id10
4205
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Taiz and Zeiger. 2002. Plant Physiology, 3rd Ed.
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Auxin Apical dominance
http//users.rcn.com/jkimball.ma.ultranet/BiologyP
ages/A/Auxin.html
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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

Kinetin
http//pubchem.ncbi.nlm.nih.gov/
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Application cotton spraying

• Adding cytokinins to young cotton increase
  drought-resistance
• Arizona 31 US cotton, highest yield acre-1

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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 gtCytokinin Shoot growth
• gtAuxin Cytokinin Root growth

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Auxin
Cytokinin
http//users.ugent.be/pdebergh/pri/pri4ez04.jpg
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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/
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http//www.rikenresearch.riken.jp/eng/research/612
1
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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/
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Jasmonic acid Plant-insect co-evolution

• Tri-trophic interactions

Degenhardt (2009) Plant Physiology 14996-102
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Jasmonic acid Pathogen response
http//park.itc.u-tokyo.ac.jp/biotec-res-ctr/kampo
/eng/research_plant.html
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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/
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Modification of GA in rice
Miyako Ueguchi-Tanaka 2005 Nature 437, 693-698
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Spraying GA for increased fruit yield

• GA induces fruiting
• in absence of seed

http//www.extension.org/pages/31607/using-plant-g
rowth-regulators-to-increase-the-size-of-table-gra
pe-berries.Ut9EYbROmM8
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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

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Conversational Plants?

• Ethylene production increases during stress
• Drought
• Heat
• Perceived by neighboring plants
• Unstressed plants induce stress pathways

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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/
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Overview of hormone mutants
Cytokinin mutant
Brassinosteroid mutant
Cytokinin mutant closer look
Ethylene mutant grown in dark
Abscisic acid mutant
Bishopp A et al. Development 20061331857-1869
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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/mot
hers-day-2/mikado-plant-watercolor-sketch-chris-ca
rter-050910/
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(No Transcript)
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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.
http//molbio.mgh.harvard.edu/sheenweb/cytokinin_s
ignaling.html
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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

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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