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.
Only one megaspore functions and it is always one of the two larger chalazal members of the tetrad (Fig.
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.
The chalazal megaspore enlarged to become the functional megaspore and the three members nearest to the micropyle degenerated.
Pfeiffer established the sections Tuberculatae, Echinatae, Cristatae, and Reticulatae on the basis of megaspore characters and suggested that spore ornamentation indicated an evolutionary relationship.