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Early embryonic development in many plants occurs within seeds, which may remain dormant for a long period. Water uptake (imbibition) and germination occur when external cues in the environment are present. As in animals, development in plants is under the control of signals and is mediated by hormones. These signals activate pathways that may result in changes in gene expression. Genetic screens have been useful in describing signal transduction pathways in the model plant Arabidopsis thaliana.
learning outcomes
You should be able to:
Evaluate the importance of seed dormancy, and contrast it (in importance and process) with seed quiescence.
List the ways a seed can maintain dormancy, and describe with examples how each method might be overcome to achieve germination.
Explore the physical and metabolic changes a seed must undergo during the early stages of germination.
Evaluate the importance of photoreceptors in plant development and growth, and compare the action of photoreceptors with that of hormones.
Draw a simple diagram to illustrate how a genetic screen can be used to identify the genes involved in the development of plant signal transduction pathways.
Under what conditions would it be advantageous for a species to have seed dormancy broken by fire?
Fire produces ash, which enriches the soil with plant nutrients. A seed that germinates as a result of fire could have an advantage in such nutrient-
What are the similarities and differences between hormone receptors and photoreceptors?
Both hormone receptors and photoreceptors are proteins that change when bound to a signal and set off a signal transduction response in a cell. Hormones are chemical in nature (such as small molecules, proteins, and steroids), whereas photoreceptors change when light binds to them.
How would a genetic screen be used to identify a plant gene involved in seed dormancy?
Seeds would be treated with a mutagen and then planted. Those seeds that germinated immediately might have a mutation that affects dormancy. These mutant plants could be compared with wild-
You have now seen the early stages of plant development and growth, and how the environment influences these processes. We will now turn to the subject of plant hormones, which are central to the internal regulation of development. We will describe how hormones were discovered and what physiological effects they have on plants. We will emphasize how genetic screens and other methods have led to a deeper molecular understanding of the action of plant hormones.