Title: Biol 352 Lecture 10
1Biol 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
5The Structures of Brassinosteroids
- BRs are polyhydroxylated steroid hormones.
- Brassinolide (BL) is the most active BR.
6Bioassays for BRs
Bean second internode bioassay for BRs
7Bioassays for BRs
Dwarf rice lamina inclination bioassay for BRs
8BL Biosynthesis and Catabolism
1. DET2 2. DWF4 3. CPD 4. BAS1
9BR Mutants
cpd
bri1
det2
det2
(dark)
10BRs Promotes Cell Expansion
The kinetics of BR stimulation of soybean
epicotyl elongation
11BRs increase the plastic wall extensibility of
soybean epicotyls
12BRs affect microtubule organization
13BRs Promote both Cell Elongation and Cell Division
Y. Gao J. G. Chen, unpublished
14BRs 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Y. Gao J. G. Chen, unpublished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.