Growth Hormones Ethylene and Abscisic Acid

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Growth HormonesEthylene and Abscisic Acid

• Course BOT 331Plant Physiology
• March 13, 2009
• Pankaj Jaiswal
• Oregon State University
• Corvallis, OR

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Ethylene response
http//www.youtube.com/watch?vKCUceQulHdw
Pineapple flowering www.pbase.com
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Ethylene production and respiration
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Ethylene and fruit ripening
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Ethylene Biosynthesis
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Role of Auxin and Ethylene during leaf abscission
formation and senescence
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The pathway summary The RAN1 protein is
essential for assembling the Cu cofactor with the
receptor for Ethylene binding. In the absence of
Ethylene, the receptor activates the downstream
kinase CTR1 that in turn inhibits the
response/gene expression. On the contrary in
the presence of Ethylene, the receptor is
inhibited so is the CTR1 kinase. The response
is now on. The kinase cascade in Ethylene
response serve as a negative regulator of the
gene expression.
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Ethylene and role in submergence
Rice SUB1 gene an ethylene response factor
provides submergence tolerance to the
plant. http//www.youtube.com/watch?vY42eWufLx5s

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Ethylene Things to Remember

• Major hormone regulating fruit ripening
• Two types of fruit based on amount of ethylene
  produced and respiration (definitions and example
  plant names mentioned in HANDOUT)
• Climacteric fruits
• Non-climacteric fruits
• Induce flowering in Pineapple
• Promotes root hair growth
• Induces triple response (inhibition and swelling
  of hypocotyl, inhibition of root elongation and
  exaggeration of the curvature of the apical hook
• S-Adenosyl Methionine derived from Methionine is
  the precursor for its biosynthesis
• ACC-Synthase and ACC-Oxidase are the two rate
  limiting enzymes in its pathway
• The Ethylene response factors contributes
  submergence tolerance in rice and Tomato
• Induce leaf senescence and abscission tissue
  formation

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Abscisic Acid (ABA)
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Vivipary
www.bio.uu.nl/mpp/images/ViviparyWheat.jpg
sparkleberrysprings.com
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ABA Biosynthesis
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Review GA promotes seed germination
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Roles of ABA in plants

• Contributes to Seed Dormancy
• Two types of dormancy
• Primary seed dormancy
• Secondary seed dormancy
• ABA accumulation in the mature seeds
• ABA promotes seed storage reserve (proteins and
  carbohydrates) and desiccation tolerance
• Seed coat and embryo can cause dormancy
• Dormancy is controlled by ABA/GA ratio
• ABA inhibits GA-induced enzymes

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Roles of ABA in plants

• Under Abiotic stress conditions such as
  drought/water stress it promotes root growth and
  suppresses shoot growth
• Plays role in closing stomata in response to
  water stress
• May play a role in flowering control
• Role in senescence and Abscission layer formation

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Grain shattering and Abscission layer formation
in rice
Genetics. 2006 June 173(2) 9951005
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ABA Things to Remember

• Regulates seed dormancy
• Seed dormancy is is of two types namely the
  primary and secondary (see handout)
• Vivipary in seeds
• ABA/GA ratio controls seed dormancy
• Induces Abscission tissue formation leading to
  senescence and shattering of leaf and fruits.
• Similar to Gibberellic Acid the precursor
  molecule for Biosynthesis is Gerany-Geranyl-pyroph
  osphate (GGPP)
• Under Abiotic stress conditions such as
  drought/water stress it promotes root growth and
  suppresses shoot growth
• Inhibits flowering by interacting with Flowering
  time control gene (FCA) in Arabidopsis