Are plants alive? Do they do anything interesting? Ask these questions to any number of high school or college students and be prepared for a variety of answers! Even biology majors may give surprising responses. Teaching the basics of plant biology and capturing students' interest can be a daunting task. Nonetheless, plants are an integral and essential part of our living world, and learning about them is a necessary component of any liberal or specialized education; thus finding better ways to teach about plants is a challenge. A Model Approach Using model plant systems can be an effective way to develop compelling exercises and experiences for students. But for an organism to be useful in teaching plant biology, it must be interesting, simple to learn about and use, easy to grow and manipulate, and applicable to a broad range of disciplines and educational levels. C-Fern™, a specially derived cultivar of the tropical homosporous fern, Ceratopteris richardii, has all of these features and offers a dynamic new approach to teaching the basic aspects of plant biology. Figure 1 C-Fern spores. The arrow indicates the spore nucleus. A principal feature of C-Fern is the rapid development of gametophytes over 2 to 3 weeks. Under optimum conditions, spores (Fig. 1) germinate 3 to 4 days from starting (DFS) the culture and develop to maturity by 10 to 12 DFS. The presence of 2 distinct sexes, males and hermaphrodites (Fig. 2), provides yet another interesting feature. Control of sexual differentiation depends on a chemical signal or pheromone. In the absence of the signal, early germinating gametophytes develop into hermaphrodites that synthesize and secrete the pheromone. Figure 2 Ten-day-old hermaphrodite, left, and male, right, C-Fern gametophytes. This then affects later germinating gametophytes that develop into males. The presence of males with many sperm-containing antheridia (Fig. 3) allows students to visualize directly hundreds of swimming sperm that are released when water is added to the culture. Sperm are chemotactically attracted to eggs and form large frenetic swarms around mature archegonia on hermaphroditic gametophytes. Figure 3 Close-up of male gametophyte with numerous antheridia. Students can view all phases of gametophyte growth and differentiation, fertilization, and early embryo development (Fig. 4) using a stereomicroscope and/or compound microscope. This demonstration of sex by a plant showing distinctive sexual types and actively swimming sperm that seek out and fertilize receptive eggs fascinates students. It provides a dynamic exposure to basic aspects of gametophyte development, sexual differentiation, pheromonal/chemical control of development, and plant sexual reproduction and alternation of generations. Figure 4 A polka dot gametophyte with a young green (wild type) sporophyte embryo.

Extended culture and observations of the sporophyte phase (Fig. 5) can also be carried out, culminating in the production of haploid spores to complete the life cycle. Figure 5 Mature fertile C-Fern sporophyte. While not as rapid in development as the gametophyte generation, sporophytes readily develop into macroscopic plants with roots and leaves. Unlike many ferns, a C-Fern sporophyte lacks a long-lived horizontal woody rhizome. Instead, it grows very much like an upright annual with erect leaves (fronds) and a short stem. Low-maintenance sporophyte cultures can be established in a simple terrarium (a 2-L plastic drink bottle works fine). The entire life cycle, spore-to-spore, can be completed in less than 90 days. Versatile and Easy C-Fern is both student and teacher friendly. Because they are free-living and autotrophic, both gametophytes and sporophytes can be cultured on a simple inorganic medium. Easy and foolproof sterile culture techniques are available for gametophyte cultures, and all stages can be conveniently cultured and manipulated with minimal training and equipment. Getting started can be as easy as boiling water. Pour pre-made C-Fern Basic Medium directly into sterile petri dishes after heating it in a boiling-water bath. C-Fern spores are available in presterilized, premeasured units, and cultures can be inoculated by simply adding sterile water and dispensing the spores onto nutrient medium. After inoculation, the cultures are ready to go under the lights to initiate growth and development. Because the basic medium contains no carbon source (e.g., sugar), the likelihood of airborne contamination is greatly reduced. Gametophyte cultures of C-Fern are easy to maintain. Use a simple fluorescent lighting fixture (Fig. 6) to provide continuous illumination Figure 6 Student using stereomicroscope and petri dish with fluorescent lighting and culture dome setup in the background. . By maintaining cultures in closed culture domes (plastic trays with clear covers), distance from the lighting fixture can be adjusted to achieve an optimum temperature within the culture dome of about 28º C (82º F). Culture domes also allow easy handling of a number of cultures, reduce the possibility of contamination, and buffer against changes in room temperature and humidity.

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