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Biol 352 Lecture 10 Brassinosteroids February 7, 2007

Biol 352 Lecture 10 Brassinosteroids February 7, 2007. 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.

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Biol 352 Lecture 10 Brassinosteroids February 7, 2007

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  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 • 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 BRs Promote both Cell Elongation and Cell Division Y. Gao & J. G. Chen, unpublished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 BRs Promote both Cell Elongation and Cell Division Y. Gao & J. G. Chen, unpublished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.

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