{'fraction_non_alphanumeric': 0.036972704714640196, 'fraction_numerical': 0.008436724565756825, 'mean_word_length': 4.850507982583454, 'pattern_counts': {'":': 0, '<': 0, '<?xml version=': 0, '>': 0, 'https://': 0, 'lorem ipsum': 0, 'www.': 2, 'xml': 0}, 'pii_count': 0, 'substrings_counts': 0, 'word_list_counts': {'cursed_substrings.json': 0, 'profanity_word_list.json': 0, 'sexual_word_list.json': 0, 'zh_pornsignals.json': 0}}
Light-Mediated Germination in Lettuce Seeds: Resurrection of a Classic Plant Physiology Lab Exercise

[ILLUSTRATION OMITTED] Most students are taught that plants use light for photosynthetic energy conversion. However, many students do not realize that plants also use light as a source of information that is translated into changing growth and development. In 1952, H.A. Borthwick and colleagues demonstrated that light controls germination in certain varieties of lettuce seeds. They found that red light was most effective at inducing germination of imbibed Grand Rapids var. lettuce seeds whereas far-red light inhibited germination. They also discovered that when lettuce seeds were given multiple exposures of one light color followed by the other, it was the last light treatment that determined the germination response. This classic study demonstrated that red and far-red light act as an "on" and "off" switch to regulate seed germination (Borthwick et al., 1952). These observations ultimately led to the isolation and characterization of the red/far-red light plant photoreceptors called phytochromes (meaning "plant pigment"). Based on this publication, Grand Rapids var. lettuce seeds were used in plant physiology laboratory teaching exercises to demonstrate phytochrome mediated red\far-red control of seed germination. However, during the past 20 years, most Grand Rapids derived varieties no longer require red light to induce germination. Though having uniform seed germination is ideal from an agricultural point of view, these lettuce breeding efforts have also led to the abandonment of this laboratory exercise demonstrating how light can regulate seed germination in plants. The purpose of this project is to identify which varieties derived from Grand Rapids lettuce still maintain a light-dependent germination response. With this information, this classic laboratory exercise can be resurrected. In addition, we present a new teaching tool that demonstrates the biological relevance of light-mediated seed germination and can be used in a lower budgeted class, such as in a public high school or college. * Germination Assay Count out 50 seeds for each light treatment. The treatments will be: "dark", "FR" (far-red light), "R" (red light), and "R/FR" (red followed by far-red light). Place one or two sheets of Whatman (Maidstone, UK) #1 90 mm diameter filter paper (or some other absorbent paper) into four round, shallow petri dishes. Moisten the filter paper with distilled water so that they are damp, but not filled with standing water. In a darkroom lit by a green safety light (we use a 25A/TG, 25W, 120V, Transparent Green Party Bulb, A-19 Shape from General Electric, Fairfield, CT), place 50 seeds in the petri dish and label the dish with one of the light treatments. Wrap aluminum foil around each petri dish to create a light-tight seal (usually two layers) and let seeds imbibe (take up water) for at least one hour in the dark at room temperature. Be sure to re-label the plates after sealing with aluminum foil. After at least one hour of imbibition, place both the red light treatment dishes and the red to far-red light treatment dishes in a red light treatment chamber. Expose seeds to red light for approximately five minutes. For our experiments described here, we use red light emitting diodes (LEDs) in an E30-LED chamber (Percival Scientific, http://www.percival-scientific.com). We have also used cool white fluorescent bulbs filtered through a sheet of red (#2423) acrylic for our red light treatment. After the five-minute exposure, turn off the red light and, in the presence of the green safe light, cover the red light treatment dishes with enough aluminum foil to create a light-tight seal. Move the red to far-red light and the far-red light treatment dishes into a far-red light treatment chamber and expose for five minutes. For our experiments described here, we use far-red LEDs in an E30LED chamber (Percival Scientific, Perry, IA, http://www.percivalscientific. …