May 7 ~ May 10###Central nucleus microspore stage###The
megaspore mother cell formation
Although the presence of lead negatively influenced
megaspore germination, it was not a limiting factor for the initial growth of Regnellidium diphyllum sporophytes in the experimental conditions and concentrations tested.
Moreover, it is evident that duration of coenocytic development (time to cellularization from
megaspore stage) in Ephedra and Gnetum is considerably shorter than in cycads and Ginkgo (Table 1).
On June 20 a typical
megaspore mother cell was first observed which could be easily recognized by its large nucleus with dense cytoplasm (Fig.
The aim of this study was to investigate germination of
megaspores and initial development of sporophytes of Regnellidium diphyllum in the presence of nickel, providing information on the influence of this metal in the establishment and growth of the species.
The functional
megaspore develops into an embryo sac (ES), which increases in length, extending into the micropylar region.
Fifteen sporocarps were cracked, thus liberating the spores, and the
megaspores were separated manually from the microspores under a stereo-microscope.
megasporocyte:
Megaspore mother cell; this diploid cell undergoes meiosis to produce four haploid
megaspores in the ovules of angiosperms.
The micropylar cell is functional
megaspore that survives and will function in megagametophyte development.
First division restitution for 2n
megaspore formation normally occurs because of asynapsis or desynapsis, suggesting that the resultant 2n gametes will likely be homogeneous.
In all accessions of these eight species, a single nucellar cell in the micropylar end of the ovule enlarged and underwent meiosis to produce a linear tetrad of
megaspores. The chalazal
megaspore enlarged to become the functional
megaspore and the three members nearest to the micropyle degenerated.
As more was learned about the biology of these furtive fern allies, it became evident that
megaspore ornamentation was of limited use in establishing relationships within the genus because of the convergence of spore features (Hickey, 1986).