A pollen tube delivers male cells to the embryo sac

When a pollen grain lands on the stigma of a compatible pistil, it germinates. Germination, for a pollen grain, is the de-

Cell Membrane Transport Pollen Tube
39.4 Pollen Tubes Begin to Grow These pollen grains have landed on hairlike structures on the stigma of an Arabidopsis flower, and pollen tubes have penetrated the stigma.

velopment of a pollen tube (Figure 39.4). The pollen tube either traverses the spongy tissue of the style or, if the style is hollow, grows downward on the inner surface of this female organ until it reaches an ovule. The pollen tube may grow millimeters or even centimeters in the process.

The rapid growth of the pollen tube requires calcium ions, which are taken up by the growing tip of the tube, as well as cell adhesion proteins. The downward growth of the pollen tube is believed to be guided by a long-distance chemical signal from the synergids within the ovule. If one synergid is destroyed, the ovule still attracts pollen tubes, but destruction of both synergids renders the ovule unable to attract pollen tubes, and fertilization does not occur.

Tube cell

Tube cell

Generative Fertilization

Generative cell

Tube cell nucleus

Synergids

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

Generative cell

Tube cell nucleus

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Responses

  • stephanie
    What is the pollen tube nucleus guided by?
    8 years ago
  • pasi
    What is the pollen tube delivers?
    8 years ago

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