Chapter 38 Lecture Enrichment Ideas
Many students have not directly experienced farming and gardening or seen the phenomena discussed here; therefore substantial actual examples can be brought to class or audiovisuals can be used to picture the various plant "behaviors."
Care should be taken not to confuse students with the pseudoscience surrounding plants being able to hear music, etc.; only animals have nervous systems and muscles, and the mechanisms described from plants are very distant from animal systems for behavior.
Describe the kinds of hormones you might find in a rooting compound sold in garden stores, and compare the stores’ expectations with what you find on the label of such compounds.
Explain the effects of auxins and cytokinins on the undifferentiated callus of plant tissue in culture, where auxins produce root tissue development and cytokinins produce shoot development.
Consider the actions of ethylene, which is produced by a ripening fruit and causes its continued ripening. This is an example of positive feedback, not a reversible reaction.
Discuss how the chemical changes of Pr to Pfr in the presence of red (normal) light and of Pfr to Pr in the presence of far-red (twilight) light or darkness are associated with the actions of long-day and short-day flowering plants. Pfr acts to stimulate flowering in a long-day plant and acts to inhibit flowering in a short-day plant, which explains the effects of a short burst of light in the middle of darkness in both kinds of plants.
There is an intuitive but erroneous presumption that long- and short-day plants must, therefore, respond to the daylight period "because the name says so."
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