When the female gametophyte (embryo sac) develops from a single megaspore, it is called monosporic development. Usually, in most angiosperms, the megaspore mother cell divides by meiosis to form four haploid megaspores arranged in a linear fashion.
An embryo sac is said to form when the haploid megaspore nucleus divides. It possesses two haploid nuclei and six haploid cells which do not have cell walls. At the event of fertilisation, one male nucleus and egg nucleus combine for the formation of zygote leading to the development of the embryo.
The embryo sac develops from the chalazal megaspore. Its nucleus divides thrice to form eight nuclei. This type is known as normal or polygonum type (first time described in polygonum divaricatum by Starsburger) of embryo sac. -Embryo sac in plants helps in developing the egg cell or nucleus after fertilization.
When the mature embryo sac is organized in an egg apparatus with a uninucleate central cell it is said to be oenothera type. A third division is absent and all the nuclei are situated in the micropylar region of the developing embryo sac. Hence a lower polar nucleus and antipodal cells are absent.
The monosporic eight-nucleate embryo sac, formed by three di- visions of the nucleus of the functioning megaspore, occurs in at least 70% of the angiosperms so far studied. Usually it is the chalazal megaspore which functions, and the remaining three soon degenerate, but there are exceptions.
The correct option is central cell. In embryo sac there are two female gametes (egg cell and central cell). The egg cell contains single nucleus and the central cell has 2 haploid nuclei called the polar nuclei . The egg and the central cell with two polar nuclei are directly involved in fertilization.
Both the nuclei of the functional dyad take part in the formation of embryo sac. Each nucleus undergoes two mitotic divisions and the mature embryo sac is 8 nucleated. The eight nuclei are organised into antipodals, egg apparatus and polar nuclei as in Polygonum type of embryo sac.
Complete answer: The development of the female gametophyte is considered monosporic growth from a single functional megaspore. The functional megaspore nucleus breaks mitotically to form two nuclei that shift to opposite poles. A two-nucleate embryo sac forms this.
Monosporic embryo sac develops from a single megaspore and as such all the nuclei present in this type of embryo sac are genetically similar. Develops from one of the two dyads formed as a result of the first meiotic division (Meiosis I) of Megaspore Mother Cell.
Megasporogenesis refers to the development of megaspores from the megasporocyte, the cell that undergoes meiosis. Meiosis of the megasporocyte nucleus results in the formation of four haploid megaspore nuclei. In most taxa, meiosis is followed by cytokinesis, resulting in four megaspore cells.
The female gametophyte develops within the ovule and generally consists of three antipodal cells, one central cell, two synergid cells, and one egg cell (Figures 1A and 1B). The female gametophyte is also commonly called the embryo sac or megagametophyte.
The mature embryo sac consists of four cell types; the egg cell and the two synergids at the micropylar end, the antipodals at the chalazal end and the central cell containing the two polar nuclei and a large central vacuole (B).
Function of embryo sac in plants: It the megaspore of a seed-bearing plant, situated within the ovule, giving rise to the endosperm and forming the egg cell or nucleus from which the embryo plant develops after fertilization.
The synergid cells direct pollen tube growth to the female gametophyte. It makes possible the access of the tube into the embryo sac. Complete answer: As these 8 nuclei are derived from the mitotic divisions of the haploid megaspore, these are haploid and thus, the synergids are haploid cells.
Synergid cells are two specialized cells that lie adjacent to the egg cell in the female gametophyte of angiosperms and play an essential role in pollen tube guidance and function. The synergids are also essential for the cessation of pollen tube growth and release of the sperm cells.
The male gametophyte (pollen or microgametophyte) develops within the anther, whereas the female gametophyte (embryo sac or megagametophyte) is a product of the ovule. The ovule is the source of the megagametophyte and the progenitor of the seed.
Drusa type:All the nuclei undergo two divisions and form 16 nuclei, out of which four nuclei remain towards the micropyle and the rest twelve at the chalazal end.
The pollen tube is guided by the chemicals secreted by the synergids present in the embryo sac; it enters the ovule sac through the micropyle. The fertilized ovule forms the seed, whereas the tissues of the ovary become the fruit, usually enveloping the seed.
