Use the Following Information When Answering the Corresponding Questions)

question 55

Multiple Choice

Use the following information when answering the corresponding questions) .
The shade avoidance response is a plant's way of changing its growth pattern when it is being shaded by another plant. Upon to shade, many plants will grow taller, flatten their leaf angle, and extend their leaves further from their stems in order to reac sunlight. Research performed by Pierik et al. Interactions between ethylene and gibberellins in phytochrome- mediated shade avoidance responses in tobacco. 2004. Plant Physiology 136:2928- 36; online at "http://www.plantphysiol.org/cgi/content/full/136/2/2928) " http://www.plantphysiol.org/cgi/content/full/136/2/2928) examined the role of ethylene and gibberellins on the shade avoidance response in tobacco plants. The shade avoidance response is known to involve phytochromes.
-When tobacco plants were exposed to far- red light, they exhibited increased stem length, petiole length, and petiole angle. These three responses are part of the shade avoidance response. When the same plants were exposed to small concentrations of ethylene while being exposed to far- red light, they exhibited even greater increases in stem length, petiole length, and petiole angle. In a subsequent experiment, tobacco plants showed an increase in ethylene production in response to far- red light. Moreover, mutant plants that are insensitive to ethylene did not show a shade avoidance response when exposed to far- red light. Taken together, these data suggest that ethylene

• A) stimulates growth when tobacco plants are shaded by other plants.
• B) inhibits growth when tobacco plants are shaded by other plants.
• C) triggers leaf abscission when tobacco plants are shaded by other plants.
• D) is not involved in the shade avoidance response.

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