Craig Evans
Bio 102-014 Phytochromes cause differences in lettuce seed germination
Abstract Plants use photoreceptors called phytochromes to discern what wavelength of light is being absorbed and respond accordingly. This experiment tests what happens when three different types of lettuce seeds are exposed to white light, red light, far-red light, and darkness. Lettuce seeds were placed in petri dishes and exposed to different wavelengths of light. The number or germinated seeds was recorded after 48 hours. The experimental hypothesis was that if seeds are exposed to white or red light, then these seeds will begin germinating, while at the same time if seeds are exposed to far-red light or left in darkness, then these seeds will have little to no germination. The main findings of this experiment did not match the hypothesis as seeds germinated regardless of the wavelength or amount of light.
Introduction
An experiment was conducted with the purpose of observing the effects of white light as a positive control, red light, far-red light, and darkness as a negative control on germination of three different types of lettuce seeds. All plants monitor the ambient light conditions. They use several informational photoreceptors, including red/far-red light absorbing phytochromes. (Shikata et al. 2014) This study was performed in order to analyze the phytochrome activation of germination under these conditions. When phytochromes sense red/far-red light it triggers an abundance of physiological responses in plants. (Wu et al. 2011) The experimental hypothesis was that if seeds are exposed to white or red light, then these seeds will begin germinating, while at the same time if seeds are exposed to far-red light or left in darkness, then these seeds will have little to no germination. The null hypothesis was that if these seeds are exposed to any amount of light from any wavelength, there will be no effect on germination.
Materials and Methods This experiment required 12 petri dishes that were obtained in the dark using only a green safelight. These petri dishes were labeled properly with all pertinent information such as the type of lettuce seed and light treatment. Twelve pieces of filter paper were placed in the petri dishes along with two to three droppersful of water. Approximately 25 lettuce seeds were placed in each of petri dishes. The petri dishes were then exposed to different light treatments for ten minutes. One set of three petri dishes, containing Concept lettuce seeds, Waldmann lettuce seeds, and Two-star lettuce seeds respectively were exposed for ten minutes to each of the four light treatments (white, red, far-red, and darkness.)
Results
The Concept lettuce seeds had 23 of 25 germinate in white light, 25 of 25 germinate in red light, 25 of 25 germinate in far-red light, and 23 of 25 germinate in darkness. The Waldmann lettuce seeds had 25 of 25 germinate in white light, 22 of 25 germinate in red light, 13 of 25 germinate in far-red light, and 21 of 25 germinate in darkness. The Two-star lettuce seeds had 21 of 25 germinate in white light, 23 of 25 germinate in red light, 19 of 25 germinate in far-red light, and 23 of 25 germinate in darkness. The accuracy and precision of all lettuce seeds exposed to white and red was as expected. The accuracy and precision of all lettuce seeds exposed to far-red light was not as expected. Even though the numbers of lettuce seeds that germinated in darkness were precise, they were not at all accurate for any of the three types of seeds.
Table 1: Concept lettuce seed germination after ten minutes of light exposure
Type of light exposure
Total number of seeds
Number of seeds germinated
Percentage (%) of seeds germinated
White
25
23
92
Red
25
25
100
Far-red
25
25
100
Darkness
25
23
92
Table 2: Waldmann lettuce seed germination after ten minutes of light exposure
Type of light exposure
Total number of seeds
Number
