In Vitro Development of Gametophyte and Sporophyte in Several Fern Species
The in vitro differentiation of the gametophyte and sporophyte of Pteridophyta, conducted through the culture, on nutritive media, of the green, incompletely differentiated sporangia and spores, exhibits a variety of peculiarities. Whereas in the case of the spore culture, a single prothallus is usually obtained out of the spore, in the case of the green sporangia (sori) culture, a group (colony) is obtained out of a single explant, a group which is made up of numerous prothalli. The agarized medium ensures a much better physical support for forming larger colonies. The secondary gametophytes can be formed through: the branching out of the prothallic filaments (each ramification representing the intial stage for the development of a new prothallus); the elongation of the cells in the apical area of the gametophyte, (which represent the initial cells of the new prothalli); out of the cells located in the base area of the prothalli, (cells which also function as prothalian initial); out of ramifications of the prothalli. The formation of the sporophyte may be the result of amphimixis, e.g. in Cystopteris fragilis, or of apomixis (apogamy) in Cyrtomium falcatum and Phegopteris connectilis. In the amphimixic species, the embryo is formed after three months from the culture initiation. What is characteristic of the apogamous species is the presence of the tracheides in the gametophyte, and the absence of the root in the first stages of development. The culture of green sporangia on agarized media is recommended, due to the fact that a very large number of gametophytes, and subsequently little plants, are formed.
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