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Study Questions

1. What is a bioassay and how did bioassays lead to the discovery of auxin?
   
   
2. What is the primary precursor for auxin biosynthesis, and where is auxin synthesized in the plant?
   
   
3. How are free auxin levels regulated by conjugation and oxidation?
   
   
4. What is meant by the “polar transport” of auxin? How is it measured? What physiological processes are affected by polar transport?
   
   
5. Does auxin also move nonpolarly? Explain your answer.
   
   
6. What are the main features of the chemiosmotic model for polar auxin transport? What is the evidence in support of the model?
   
   
7. Discuss the roles of PIN proteins, ABCB transporters, and AUX/LAX carriers as auxin transporters mediating polar transport.
   
   
8. What are some inhibitors of polar transport, and how are they thought to work? What compounds might act as endogenous inhibitors of polar transport in plants?
   
   
9. How are auxin transport proteins secreted to the plasma membrane? How might TIBA and NPA inhibit polar transport?
   
   
10. What is the nature of the auxin receptor?
    
    
11. How does auxin’s binding to its receptor lead to gene expression?
    
    
12. What is a typical lag time for auxin-induced elongation?
    
    
13. Draw a typical dose-response curve for auxin-induced stem or coleoptile elongation. What happens at high doses?
    
    
14. Describe the acid growth hypothesis of auxin action. What is the evidence that supports it?
    
    
15. Define and give examples of “tropisms” in plants.
    
    
16. What is the Cholodny–Went model for tropisms in response to light and to gravity, and what evidence supports it in both cases?
    
    
17. What structure or structures act as gravity receptors in plant cells? Where are these structures located in shoots and roots?
    
    
18. Discuss the cellular pathways and molecular mechanisms of auxin movement in root tips during gravitropism. Which components of the pathway seem to be able to respond to gravity?
    
    
19. Discuss how auxin regulates the following developmental phenomena: apical dominance, lateral and adventitious roots, leaf abscission, floral bud development, vascular differentiation, and fruit development.