Male Gametophyte: The Pollen Grain

The male gametophyte develops and reaches maturity in an immature anther. In a plant’s masculine reproductive organs, breakthrough of pollen takes ar in a structure recognized as the microsporangium (Figure 1). The microsporangia, which are usually bilobed, space pollen sacs in i m sorry the microspores develop into pollen grains. These are discovered in the anther, which is at the finish of the stamen—the lengthy filament that supports the anther.

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Figure 2. Pollen establishes from the microspore mother cells. The maturation pollen serial is created of 2 cells: the pollen tube cell and the generative cell, i m sorry is within the pipe cell. The pollen grain has two coverings: an inner great (intine) and also an external layer (exine). The inset scanning electron micrograph mirrors Arabidopsis lyrata pollen grains. (credit “pollen micrograph”: alteration of work by Robert R. Wise; scale-bar data native Matt Russell)

Figure 3. As shown in this chart of the embryo sac in angiosperms, the ovule is extended by integuments and also has one opening referred to as a micropyle. Within the embryo sac are three antipodal cells, 2 synergids, a main cell, and also the egg cell.

While the details may vary between species, the overall breakthrough of the female gametophyte has two unique phases. First, in the process of megasporogenesis, a solitary cell in the diploid megasporangium—an area of organization in the ovules—undergoes meiosis to develop four megaspores, only among which survives. During the second phase, megagametogenesis, the making it through haploid megaspore experience mitosis to create an eight-nucleate, seven-cell woman gametophyte, also known together the megagametophyte or embryo sac. 2 of the nuclei—the polar nuclei—move come the equator and also fuse, creating a single, diploid main cell. This central cell later on fuses with a sperm to form the triploid endosperm. 3 nuclei place themselves top top the end of the embryo sac opposite the micropyle and develop right into the antipodal cells, which later on degenerate. The nucleus closest to the micropyle i do not care the female gamete, or egg cell, and also the two nearby nuclei construct into synergid cell (Figure 3). The synergids assist guide the pollen tube for successful fertilization, ~ which castle disintegrate. Once fertilization is complete, the result diploid zygote creates into the embryo, and also the fertilized ovule creates the various other tissues the the seed.

A double-layered integument protects the megasporangium and, later, the embryo sac. The integument will develop into the particle coat after ~ fertilization and protect the entire seed. The ovule wall will become component of the fruit. The integuments, when protecting the megasporangium, execute not enclose that completely, yet leave an opening dubbed the micropyle. The micropyle allows the pollen pipe to go into the woman gametophyte for fertilization.

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Practice Question

An embryo sac is lacking the synergids. What certain impact would certainly you mean this to have actually on fertilization?

The pollen tube will be can not to form.The pollen pipe will type but will not be guided toward the egg.Fertilization will certainly not occur because the synergid is the egg.Fertilization will certainly occur yet the embryo will not have the ability to grow.