Biol 352 Lecture 10

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Biol 352 Lecture 10 Brassinosteroids February
7, 2007
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• Review ABA
• ABA is the major hormone responsible for seed
  dormancy and water stress response.
• Key enzymes for biosynthesis ZEP (ABA1), NCED
  (VP14), and ABA-aldehyde oxidase (ABA3).
• ABA antagonizes the action of GA in seed
  germination.
• ABA controls stomatal guard cell closure/opening.
  
• ABA signaling in stomatal guard cells Ca2, K,
  H.

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• Lecture Outline
• Chemical structure of Brassinosteroids (BRs)
• Bioassays for BRs
• Biosynthesis of BRs
• Function of BRs cell elongation and cell
  division
• Summary

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• Learning Objectives
• Learn to use bioassays to distinguish BRs from
  other plant hormones
• Define key enzymes in BR biosynthesis
• Determine the role of BRs in cell elongation and
  cell division
• Reading
• 4th Ed, Plant Physiology, Taiz Zeiger, Chapter
  24 p617-633

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The Structures of Brassinosteroids

1. BRs are polyhydroxylated steroid hormones.
2. Brassinolide (BL) is the most active BR.

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Bioassays for BRs
Bean second internode bioassay for BRs
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Bioassays for BRs
Dwarf rice lamina inclination bioassay for BRs
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BL Biosynthesis and Catabolism
1. DET2 2. DWF4 3. CPD 4. BAS1
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BR Mutants
cpd
bri1
det2
det2
(dark)
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BRs Promotes Cell Expansion
The kinetics of BR stimulation of soybean
epicotyl elongation
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BRs increase the plastic wall extensibility of
soybean epicotyls
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BRs affect microtubule organization
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BRs Promote both Cell Elongation and Cell Division
Y. Gao J. G. Chen, unpublished
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BRs Promote both Cell Elongation and Cell Division
Y. Gao J. G. Chen, unpublished
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• Summary
• Brassinosteroids (BRs) are polyhydroxylated
  steroid hormones. Brassinolide (BL) is the most
  active BR.
• Bioassays can be used to distinguish BRs from
  other plant hormones.
• Deficiency in BR biosynthesis results in
  dwarfism.
• BRs promote both cell elongation and cell
  division.