A basic laboratory investigation using C-Fern to examine spore germination, gametophyte development, and events surrounding sexual reproduction including swimming sperm.
- C-Fern Spores (C-Fern spores are easy to manipulate – they are exceptionally large for fern spores, about 120 μm diameter. Spores can be stored more or less indefinitely at room temperature. )
- Cotton Tipped Swab, one per student (Cultures sown with cotton-tipped swabs may contain some fungal, bacterial, or algal contamination. Since the culture media lacks a carbon source, contamination is usually minor and its appearance is integrated into this exercise. For axenic cultures, spores may be easily surface sterilized and aseptically inoculated.)
- Plastic Sandwich Bags, one per culture dish
- 60×15 mm Plastic Petri Dishes prepared with Basic C-Fern Nutrient Medium, one per student (About 100 Petri dishes (60×15 mm) per liter of medium can be poured. Pour dishes on a clean bench without traffic or drafts or use of a laminar flow hood. This medium gives consistent and predictable results for both C-Fern gametophytes and sporophytes.)
- Marking Pen
- Appropriate Culture Regimen or Conditions ( All culture dishes should be placed in a C-Fern Culture Dome or C-Fern Growth Pod under constant fluorescent lighting and maintained at a temperature of 28 °C. Environmental regimen (culture medium, light, and temperature) affects the precise timing of development. Lower temperatures delay development, for example, at about 22°C gametophytic development takes about twice as long.)
- Microscope and Supplies to Prepare Wet Mounts
- Probe OR toothpick OR equivalent
For this exercise, students sow spores and culture gametophytes in 60×15 mm plastic Petri dishes containing an agar solidified nutrient medium. (Composition of stock solutions and working nutrient medium (Basic C-Fern Nutrient Medium) are given in the C-Fern Manual.) This investigation is a multi-week laboratory activity that involves direct observation of critical developmental events, data collection, and synthesis. Since the establishment of cultures and subsequent manipulations and observations are not time-consuming, other botanical or developmental topics can be integrated into these laboratory sessions.
In the first week, students receive written materials that provide goals for this investigation, sufficient background on the plant life cycle, and specific step-by-step instructions for completing this investigation. For the following weeks, students are prompted to make observations through questions.
Goal: To observe the development of the gametophytic generation of a fern. You will make observations on spore germination, gametophyte ontogeny, sexual maturation, fertilization, embryo growth, and the development of the young sporophyte. You should be able to relate all of these events to the complete life cycle of a fern as well as to plants in general.
Background: The life cycle of land plants is characterized by an alternation between two phases or generations that are morphologically and functionally distinct. The gametophyte generation is the sexual phase of the life cycle. Gametophytes produce eggs and/or sperm (gametes) and house and nourish the product of fertilization, the embryo. Gametophytes may be extremely small (seed plants) or the dominant phase of the life cycle (bryophytes). Although fern gametophytes are quite small, they are free-living and independent from the much larger spore-producing plant that you are familiar with, i.e. the sporophyte. In ferns, seed plants and other vascular plants, the sporophyte is the dominant phase of the life cycle and produces spores by meiosis. Spores are haploid cells and the plant that produces spores, the sporophyte, must be diploid. This contrasts from most animals, in which meiosis yields gametes.
After spores are dispersed from the sporophyte and germinate, what do they grow into? You will answer this question (if you do not already know the answer!) by observations of developing fern spores. You will inoculate C-Fern spores onto nutrient medium