Megaspore


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Related to Megaspore: megagametophyte, generative cell

megaspore

[′meg·ə‚spȯr]
(botany)

Megaspore

 

a spore from which develops the female prothallium (in gymnosperms, the primary endosperm nucleus; in angiosperms, the embryo sac). The megaspore arises as a result of the division of the megasporocyte (mother cell). In Pteridophyta the number of mature megaspores in the megasporangium varies. The Isoetes have many megaspores. The Lepidodendron and Sigillaria have eight to 16; the Selaginella, two to four; the water ferns, only one. Megaspores grow into female prothallia either inside (Lepidodendron, Selaginella, Salvinia) or outside (Marsilea, some Selaginella) the megasporangium. The first stages in the development of the prothallium occur inside the megaspore; the membranes of the megaspore then open and the parts of the prothallium that bear the archegonia emerge (in Salvinia they turn green). In seed plants, four megaspores usually form in each nucellus (the central part of the ovule).

References in periodicals archive ?
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.
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).