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.
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).