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Biol 352 Lecture 10

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Biol 352 Lecture 10 Brassinosteroids February 7, 2007 Review: ABA ABA is the major hormone responsible for seed dormancy and water stress response. – PowerPoint PPT presentation

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Title: Biol 352 Lecture 10


1
Biol 352 Lecture 10 Brassinosteroids February
7, 2007
2
  • 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.

3
  • Lecture Outline
  • Chemical structure of Brassinosteroids (BRs)
  • Bioassays for BRs
  • Biosynthesis of BRs
  • Function of BRs cell elongation and cell
    division
  • Summary

4
  • 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

5
The Structures of Brassinosteroids
  1. BRs are polyhydroxylated steroid hormones.
  2. Brassinolide (BL) is the most active BR.

6
Bioassays for BRs
Bean second internode bioassay for BRs
7
Bioassays for BRs
Dwarf rice lamina inclination bioassay for BRs
8
BL Biosynthesis and Catabolism
1. DET2 2. DWF4 3. CPD 4. BAS1
9
BR Mutants
cpd
bri1
det2
det2
(dark)
10
BRs Promotes Cell Expansion
The kinetics of BR stimulation of soybean
epicotyl elongation
11
BRs increase the plastic wall extensibility of
soybean epicotyls
12
BRs affect microtubule organization
13
BRs Promote both Cell Elongation and Cell Division
Y. Gao J. G. Chen, unpublished
14
BRs Promote both Cell Elongation and Cell Division
Y. Gao J. G. Chen, unpublished
15
  • 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.
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