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: Reading:
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: p

5. The Structures of Brassinosteroids
BRs are polyhydroxylated steroid hormones.
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Y. Gao & J. G. Chen, unpublished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Y. Gao & J. G. Chen, unpublished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.