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Study Questions

1. What is a bioassay and how did bioassays lead to the discovery of auxin?

2. Where are auxins synthesized in the plant, and what role do they play in leaf vascular development?

3. Diagram the pathways of auxin biosynthesis in plantsand bacteria. How do these pathways differ? Which is the most common pathway in plants?

4. Discuss the relationship between IAA conjugation andIAA oxidation.

5. What are the main features of the chemisosmotic modelfor polar auxin transport? Which components of the model have been identified in plants? What is the evidence in support of the model?

6. 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?

7. Discuss the role of polar auxin transport in overall plant development. (Hint: Include a discussion of embryogenesis as discussed in Chapter 16, p. 364).

8. What is the acid growth hypothesis of auxin action, and what is the evidence that supports it?

9. Compare and contrast the acivation hypothesis vs. the synthesis hypothesis for auxin-induced proton extrusion.

10. What is the Cholodny-Went model for phototropism and gravitropism? What evidence supports the model in both cases?

11. What structure or structures act as gravity receptors in plant cells? Where are these structures located in shoots and roots?

12. 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?

13. Discuss the evidence for the role of auxin in the following physiological phenomena: apical dominance, lateral and adventitious roots, leaf abscission, floral bid development, fruit development, and vascular differentiation.

14. What is ABP1? Which auxin responses does it seem to regulate?

15. What are the five major classes of early auxin-responsive genes?

16. Diagram and discuss the current model for the role of the AUX/IAA gene family in regulating the early auxin-responsive genes.