Review Questions for Lecture 16 1 How did the tobacco mutant Maryland Mammoth lead to the discovery of photoperiodism in plants? 2. A plant can only flower when the day length is 12 hour. Can you classify it as a short-day plant? Why? 3 Day length is a determining factor in plant flowering, but day length alone is a quite ambiguous signal. How can plants avoid such an ambiguity in day-length measurement? 4 Xanthium can flower only when the day length is shorter than 15.5 hours but remain vegetative when the day-length is longer than 15.5 hours. Design an experiment to demonstrate that it is the duration of the dark period but not the duration of light period that is measured by plants to monitor day length. 5 Why do you think that phytochromes are involved in the perception of the photoperiodic signals? 6 Describe the two hypotheses that have been proposed to explain how plants measure photoperiodic time. Which one becomes the favored one in recent years? Provide a simple experiment to support this hypothesis.
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