2Review: ABAABA 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+.
3Lecture Outline: Chemical structure of Brassinosteroids (BRs) Bioassays for BRsBiosynthesis of BRsFunction of BRs: cell elongation and cell divisionSummary
4Learning Objectives: Reading: Learn to use bioassays to distinguish BRs from other plant hormonesDefine key enzymes in BR biosynthesisDetermine the role of BRs in cell elongation and cell divisionReading:4th Ed, Plant Physiology, Taiz & Zeiger, Chapter 24: p
5The Structures of Brassinosteroids BRs are polyhydroxylated steroid hormones.Brassinolide (BL) is the most active BR.
6Bioassays for BRsBean second internode bioassay for BRs
7Bioassays for BRsDwarf rice lamina inclination bioassay for BRs
8BL Biosynthesis and Catabolism 1. DET22. DWF43. CPD4. BAS1
13BRs Promote both Cell Elongation and Cell Division Y. Gao & J. G. Chen, unpublished
14BRs Promote both Cell Elongation and Cell Division Y. Gao & J. G. Chen, unpublished
15Summary: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.