Angiosperms perform double fertilization

In most angiosperm species, the mature pollen grain consists of two cells, the tube cell and the generative cell. The larger tube cell encloses the much smaller generative cell. Guided by the tube cell nucleus, the pollen tube eventually grows through the megasporangial tissue and reaches the embryo sac. The generative cell meanwhile has undergone one mitotic division and cytokinesis to produce two hap-loid sperm cells.

Both of the sperm cells enter the embryo sac, where they are released into the cytoplasm of one of the synergids. This synergid degenerates, releasing the sperm cells (Figure 39.5). Each sperm cell then fuses with a different cell of the embryo sac. One sperm cell fuses with the egg cell, producing the diploid zygote. The other fuses with the central cell, and that sperm cell nucleus and the two polar nuclei unite to form a triploid (3n) nucleus. While the zygote nucleus begins mitotic division to form the new sporophyte embryo, the triploid nucleus undergoes rapid mitosis to form a specialized nutritive tissue, the endosperm. The endosperm will later be digested by the developing embryo, as we saw in the previous chapter. The antipodal cells and the remaining synergid eventually degenerate, as does the pollen tube nucleus.

This process is known as double fertilization because it involves two nuclear fusion events:

► One sperm cell fuses with the egg cell.

► The other sperm cell fuses with the two polar nuclei.

39.5 Sperm Nuclei and Double Fertilization The sperm nuclei contribute to the formation of the diploid zygote and the triploid endosperm. Double fertilization is a characteristic feature of angiosperm reproduction.

Synergids

Initially the pollen tube contains two haploid cells, the generative cell and the tube cell.

39.5 Sperm Nuclei and Double Fertilization The sperm nuclei contribute to the formation of the diploid zygote and the triploid endosperm. Double fertilization is a characteristic feature of angiosperm reproduction.

Zygote Formation FlowersDouble Fertilization

The zygote nucleus divides mitotically, one daughter cell giving rise to the embryo proper and the other to the suspensor.

39.6 Early Development of a Eudicot The embryo develops through intermediate stages, including a characteristic heart-shaped stage, to reach the torpedo stage.

The zygote nucleus divides mitotically, one daughter cell giving rise to the embryo proper and the other to the suspensor.

Embryo r

Suspensor

The fusion of a sperm cell nucleus with the two polar nuclei to form endosperm takes place only in angiosperms. The fusion of these three nuclei, the possession of flowers, and the formation of fruit are the three most definitive characteristics shared by angiosperms.

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Responses

  • gregory carter
    Which nuclei are involved in double fertilization?
    7 years ago
  • Geraldina
    Does the tube nucleus fuse with the po0lar bodies?
    7 years ago
  • asfaha
    Why does double fertilization takes place only in angiosperms58 Views?
    1 year ago
  • Jesus Doty
    What is double fertilization zygote?
    10 months ago

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