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Study Questions

1. What is meant by “floral evocation”?
   
   
2. Distinguish between a floral meristem and an inflorescence meristem. Which type or types are present in Arabidopsis?
   
   
3. Using a labeled diagram, define the term “whorls” as applied to the structure of the floral meristem, and describe the different whorls in a typical flower, such as Arabidopsis.
   
   
4. Compare and contrast “meristem identity genes” and “floral organ identity genes,” and give examples of each.
   
   
5. Which general type of regulatory gene would be implicated in the following mutations?
   1. A mutation causing the formation of an extra whorl of stamens
   2. A mutation delaying or preventing the transition from vegetative to reproductive meristem
   3. A mutation causing the formation of petals where stamens normally develop
      
      
6. What are homeotic mutations, and how did their study contribute to an understanding of the genetic control of floral development?
   
   
7. Discuss the known floral homeotic genes in terms of the ABC model for the determination of floral organ identity.
   
   
8. Describe the phenotypes of the following homeotic mutant of Arabidopsis.
   1. Loss of B function
   2. Loss of C function
   3. Loss of A function
   4. Complete loss of A, B, and C functions
      
      
9. The regulation of the transition to flowering may be internal, external, or a combination of the both internal and external cues. What terms are used to describe these different alternatives?
   
   
10. 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?
    
    
11. What is meant by “competence” and “determination”? How can one demonstrate experimentally that a shoot meristem is florally determined?
    
    
12. What are circadian rhythms? Define and discuss the following terms in relation to circadian rhythms: “period,” “phase,” “amplitude,” “entrainment,” “zeitgebers,” “free-running,” “temperature compensation,” “subjective day,” and “subjective night.”
    
    
13. Discuss how the phenomenon of “phase-shifting” adjusts circadian rhythms to different day–night cycles.
    
    
14. Which pigments are responsible for light entrainment of circadian rhythms in plants? Which of these pigments also participates in animal circadian rhythms?
    
    
15. What is photoperiodism? What is the effect of latitude on day length and what does this suggest about the evolution of photoperiodism?
    
    
16. How did the tobacco mutant Maryland Mammoth lead to the discovery of photoperiodism in plants?
    
    
17. Name and describe five categories of photoperiodic plants, and give an example of each.
    
    
18. What part of the plant perceives the photoperiodic stimulus? (Cite the evidence.)
    
    
19. Which is more important in photoperiodism— day length or night length? How has the use of “night breaks” helped to answer this question? (Cite experimental studies.)
    
    
20. What is meant by a “circadian oscillator,” and what is the evidence that it plays an important role in photoperiodism?
    
    
21. Using labeled diagrams, describe the “Coincidence Model” for photoperiodism as it applies to both short-day plants and long-day plants. What is the significance for flowering of fluctuations in the expression of the CONSTANS gene?
    
    
22. Which pigment is the primary photoreceptor in photoperiodism and how has this been determined experimentally?
    
    
23. What is the role of the blue-light absorbing pigment, cryptochrome, in photoperiodism?
    
    
24. What is “vernalization” and where is the vernalization signal perceived in the plant?
    
    
25. Discuss the relationship between vernalization and the gene FLOWERING LOCUS C (FLC).
    
    
26. Why does the phenomenon of photoperiodism imply the long-distance transport of the floral stimulus to the shoot apex? In what tissue does this occur? (Cite the evidence.)
    
    
27. What is “florigen,” and what is the early experimental evidence used to demonstrate its existence?
    
    
28. Why did it take so long to identify florigen? What type of molecule did it turn out to be?
    
    
29. Using a labeled diagram, discuss the role of the Arabidopsis protein FLOWERING LOCUS T in flowering.
    
    
30. How are the signaling pathways involved in photoperiodism coordinated with the signaling pathways for other internal or external factors regulating flowering? Show how the gene SOC1 integrates signals from multiple pathways to control flowering in Arabidopsis.