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1. What is the primary precursor for auxin biosynthesis, and where is auxin synthesized in the plant?2. Describe a typical dose-response curve for auxin-induced stem or coleoptile elongation. What happens at high doses?3. What structure or structures act as gravity receptors in plant cells? Where are these structures located in shoots and roots?4. Discuss how auxin regulates apical dominance, lateral and adventitious roots, leaf abscission, floral bud development, vascular differentiation, and fruit development.5. How were gibberellins (GAs) discovered?6. What are the common chemical features of gibberellins, and to which general class of compounds are they related?7. Briefly describe several different physiological responses to GA.8. What are some commercial applications of GA in agriculture?9. Which pathway produces the early intermediates for GA biosynthesis? What three cellular compartments are involved in gibberellin biosynthesis, and what are the major biochemical steps in each compartment?10. Which reactions cause gibberellin inactivation?11. GA can inhibit its own synthesis by negative feedback regulation. Which steps in the GA biosynthesis pathway are down-regulated by GA?12. Considering plant hormones and regulators, how can plant height be altered through genetic engineering?13. The GA and phytochrome pathways are integrated. Compare and contrast the GA signaling pathways in dark-grown (tall) and light-grown (short) Arabidopsis hypocotyls.14. The study of which cellular process led to the discovery of cytokinin? Was the first discovered cytokinin a synthetic or naturally occurring hormone?15. Name two plant diseases that are associated with cytokinin overproduction. In each case, what is the source of the excess cytokinin?16. Compare the plant and microbial pathways of cytokinin biosynthesis. What are the naturally occurring cytokinins in plants? Which enzyme catalyzes the first step in cytokinin biosynthesis?17. Cytokinins can act both locally and over long distances in the plant. Provide examples of both types of cytokinin action. In which tissue(s) does long distance transport occur?18. Which enzyme is responsible for cytokinin degradation?19. Which protein (or proteins) represents the “response regulator” in the cytokinin signaling pathway? What is their mechanism of action?20. Discuss the roles of cytokinins in shoot growth, root growth, apical dominance, leaf senescence, and vascular development.21. What are some potential applications of cytokinin manipulation to agriculture?22. How was the plant hormone ethylene discovered?23. Which two key enzymes are rate-limiting for ethylene biosynthesis, and what reactions do they catalyze?24. How is ethylene biosynthesis promoted by other hormones, such as auxin and cytokinin?25. What are some specific inhibitors of ethylene biosynthesis and ethylene action, and how do they work?26. Discuss five different physiological responses regulated by ethylene.27. Discuss the interaction of auxin and ethylene during leaf abscission.28. What is the name of the pathway that produces Abscisic Acid? Which pigments act as intermediates in the pathway?29. Does the level of Abscisic in plant tissues fluctuate or remain constant under changing environmental conditions? Discuss the effect of water stress on ABA levels.30. How do changes in the pH of the xylem sap regulate the uptake of Abscisic Acid in leaf mesophyllcells? How would this help the leaf to survive under water stress conditions?31. What is the role of Abscisic Acid during embryogenesis?32. Discuss various types of seed dormancy. What three environmental factors can often affect a release from seed dormancy?33. What is the evidence that the ABA:GA ratio controls certain types of seed dormancy?34. 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.35. 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?36. Discuss biochemical and regulatory mechanisms for maintaining brassinosteroid homeostasis in the plant.37. Cite evidence that brassinosteroids act locally near their sites of synthesis.38. Discuss several physiological effects of brassinosteroids in plants.39. What is meant by “floral evocation”?40. What are the signals that can cause floral evocation?41. Compare “meristem identity genes” and “floral organ identity genes.”42. What are homeotic mutations, and how did their study contribute to an understanding of the genetic control of floral development?43. Discuss the known floral homeotic genes in terms of the ABC model for the determination of floralorgan identity.44. What is meant by “phase change?” Give some examples. Where in the plant does phase change occur? Why are the effects of phase change more marked in trees?45. What is meant by “competence” and “determination?”46. What are circadian rhythms and why are they important to flowering?47. Which wavelengths and pigments are responsible for light entrainment of circadian rhythms in plants?48. What is photoperiodism?49. Name and describe five categories of photoperiodic plants, and give an example of each.50. What part of the plant perceives the photoperiodic stimulus?51. Which is more important in photoperiodism— day length or night length? How has the use of “night breaks” helped to answer this question?52. What is meant by a “circadian oscillator,” and what is the evidence that it plays an important role in photoperiodism?53. Which pigment is the primary photoreceptor in photoperiodism and how has this been determinedexperimentally?54. What is “vernalization” and where is the vernalization signal perceived in the plant?55. Discuss how Arabidopsis was used to help better understand vernalization.56. Why does the phenomenon of photoperiodism imply the long-distance transport of the floral stimulus to the shoot apex? In what tissue does this

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LSU HORT 2050 - Study Guide

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