CHAPTER 22 :: Study Questions 1. What is the function of the Yang cycle during ethylene biosynthesis? 2. Which two key enzymes are rate-limiting for ethylene biosynthesis, and what reactions do they catalyze? 3. Which intermediate of ethylene biosynthesis builds up in roots during flooding, and why? What are the developmental consequences of this build-up? 4. Discuss the regulation, by various environmental factors, of the two enzymes listed in Question 3. 5. How is ethylene biosynthesis promoted by other hormones, such as auxin and cytokinin? 6. What are some specific inhibitors of ethylene biosynthesis and ethylene action, and how do they work? 7. Describe the "triple response" to ethylene in Arabidopsis. 8. Discuss how a mutant of Arabidopsis led to the identification of the ethylene receptor? What was the nature of the receptor? 9. Discuss the domain structures of the five known ethylene receptor proteins. To which general class of receptors do they belong? 10.Explain why disruptions in the regulatory domains of three or more of the ethylene receptors results in a constitutive ethylene response. 11. Using a labeled diagram, discuss the current model for the ethylene signal transduction pathway. 12. Discuss five different physiological responses regulated by ethylene. 13.Discuss the interaction of auxin and ethylene during leaf abscission
CHAPTER 23 :: Study Questions 1. Where in the cell is ABA synthesized? What are the major biochemical steps that occur in each cellular compartment? 2. Does the level of ABA in plant tissues fluctuate or remain constant under changing environmental conditions? Discuss the effect of water stress on ABA levels. 3. How do changes in the pH of the xylem sap regulate the uptake of ABA in leaf mesophyll cells? How would this help the leaf to survive under water stress conditions? 4. Discuss the roles of protein kinases and protein phosphatases in the ABA response. 5. Using a labeled diagram, discuss the main steps in ABA-regulated gene expression. 6. What is the role of ABA during embryogenesis? 7. Discuss various types of seed dormancy. What three environmental factors can often affect a release from seed dormancy? 8. What is the evidence that the ABA:GA ratio controls certain types of seed dormancy? 9. What is vivipary? Based on work with viviparous mutants of maize and Arabidopsis, speculate on the physiological mechanism of naturally occurring vivipary. 10. Discuss how ABA affects the root:shoot ratio under well-watered versus dehydrating conditions. How is ethylene involved in this response? 11. What is the evidence that calcium plays an important role as a second messenger during ABA-induced closure of stomatal guard cells? Where does the calcium come from? 12.Using a labeled diagram, discuss the participation of ABA receptors, various second messengers, changes in the membrane potential, opening and closing of ion channels, the vacuole, and the plasma membrane proton pump in bringing about stomatal closure in response to ABA. Which occurs first, cation efflux or anion efflux?
CHAPTER 24 :: Study Questions 1. Describe two different bioassays for brassinosteroids. 2. Using a labeled diagram, describe the current model for the brassinosteroid signaling pathway. Include events occurring on the plasma membrane, the cytosol, and the nucleus. 3. What roles do phosphorylation, repressor proteins, and the 26S proteasome play in the BR signaling pathway? 4. What do brassinosteroids, gibberellin, and abscisic acid have in common with respect to biosynthesis? What is the name of the most physiologically active BR, and what is its immediate precursor? 5. Discuss biochemical and regulatory mechanisms for maintaining brassinosteroid homeostasis in the plant. 6. Discuss several physiological effects of brassinosteroids in plants.